CN118318101A

CN118318101A - Controller for wind turbine generator

Info

Publication number: CN118318101A
Application number: CN202280076190.8A
Authority: CN
Inventors: F·卡波内蒂; J·D·格朗内特; E·尼尔森
Original assignee: Shanghai Electric Wind Power Group Co Ltd
Current assignee: Shanghai Electric Wind Power Group Co Ltd
Priority date: 2021-11-19
Filing date: 2022-11-18
Publication date: 2024-07-09
Also published as: DK202170574A1; DK181379B1; WO2023088416A1

Abstract

A controller for providing cyclic independent pitch control (ipc) of a plurality of blades of a wind turbine, the controller configured to: receiving at least a first pitch angle control signal and a second pitch angle control signal for controlling the pitch of the blade; receiving wind direction information; determining a first pitch angle control output signal based on the first pitch angle control signal and determining a second pitch angle control output signal based on a second pitch angle control signal; and providing one or more control signals for implementing cycle ip with a predetermined phase shift if the wind direction is on a first side of the wind turbine; if the wind direction information indicates the wind direction incident on the second side of the wind turbine, one or more control signals for implementing cycle I PC are not provided with a predetermined phase shift.

Description

Controller for wind turbine generator

Technical Field

The invention relates to a controller for a wind turbine generator. In particular, it relates to a controller for a wind turbine, the controller being configured to detect rapid changes in wind direction. It also relates to a controller configured to implement cyclic independent vane control actions. The invention also relates to a wind turbine comprising such a controller; a method for effecting cyclic independent vane control actions; and a computer program product and computer program code for implementing the method.

Background

Wind turbines generally include a tower and a rotor mounted to the tower. The wind rotor includes a hub and a plurality of blades configured to extend from the hub. A wind turbine typically comprises three blades, but other numbers of blades are possible. Each blade is operatively coupled to the hub by a blade bearing that allows the blade to rotate relative to the hub such that the pitch of the blade is adjustable. The wind rotor is connected to the generator and may be connected to the generator through a gearbox. The generator is configured to convert rotational energy of the wind rotor into electrical energy. The generator and optional gearbox are located within the nacelle. The main bearings support the wind rotor and allow the wind rotor to rotate relative to the nacelle and the generator. In some examples, the wind turbine may include a brake to slow and stop rotation of the rotor.

Wind turbines may experience rapid changes in wind direction and/or rapid changes in wind speed during operation. These rapid changes may cause extreme loads on the main bearings and other components of the wind turbine and may introduce undesirable vibrations. To control the loads and vibrations experienced during rapid changes in wind direction and/or wind speed, the controller of the wind turbine may provide control actions to alleviate the problem or shut down the wind turbine. Detecting rapid changes in wind direction and/or wind speed events and providing control measures in time is a challenge.

Disclosure of Invention

According to a first aspect of the invention we provide a controller for providing cyclic independent pitch control of a plurality of blades of a wind turbine, wherein the controller is configured to:

Receiving at least a first pitch angle control signal and a second pitch angle control signal for controlling the pitch of the blades during cyclic independent pitch control, wherein the first pitch angle control signal and the second pitch angle control signal define a change in blade pitch of the plurality of blades during rotation of the rotor;

Receiving wind direction information, wherein the wind direction information indicates wind directions incident on a wind turbine generator set relative to a direction faced by the wind turbine generator set;

determining a first pitch angle control output signal based on the first pitch angle control signal and determining a second pitch angle control output signal based on a second pitch angle control signal; and

Providing one or more control signals for implementing cyclic independent pitch control of blades of the wind turbine, based on the first and second pitch angle control output signals, with a predetermined phase shift, if the wind direction information indicates a wind direction incident on a first side of the wind turbine;

If the wind direction information indicates a wind direction incident on a second side of the wind turbine, opposite the first side, one or more control signals for implementing cyclic independent pitch control of blades of the wind turbine are provided based on the first pitch angle control output signal and the second pitch angle control output signal, not with the predetermined phase shift.

Thus, in one or more examples, the pitch sequence of rotor rotation provided by the one or more control signals for the cyclic IPC will be out of phase with the pitch sequence of rotor rotation provided by the one or more control signals for the cyclic IPC when the wind is on one side, which has been found to be advantageous.

In one or more examples, the wind direction information is derived from one or more sensors. The one or more sensors may include an acceleration sensor. In one or more examples, the wind direction information is from a wind direction sensor.

In one or more examples, the wind turbine has two blades, and the first pitch angle control signal is used to control a first of the two blades, and the second pitch angle control signal is used to control a second of the two blades. In other examples, the wind turbine has three blades and three corresponding pitch angle control signals are provided.

In one or more embodiments, the first pitch angle control signal includes a D component for controlling a direct-to-quadrature axis shift of a pitch of the blade during cyclic independent pitch control; and the second pitch angle control signal comprises a Q component for controlling a direct-to-quadrature axis shift of a pitch of the blade during cyclic independent pitch control.

Thus, in one or more examples, the wind turbine has three blades, and the D component and the Q component thereby comprise two pitch angle control signals for controlling the pitch of the three blades.

In one or more embodiments, the controller is configured to:

Determining the first pitch angle control output signal by applying the predetermined phase shift to the first pitch angle control signal and the second pitch angle control output signal by applying the predetermined phase shift to the second pitch angle control signal if the wind direction information indicates a wind direction incident on the first side of the wind turbine, thereby providing the one or more control signals for implementing cyclic independent pitch control of the blade in the presence of the predetermined phase shift; and

If the wind direction information indicates a wind direction incident on the second side of the wind turbine, determining the first pitch angle control output signal by not applying the predetermined phase shift to the first pitch angle control signal and determining the second pitch angle control output signal by not applying the predetermined phase shift to the second pitch angle control signal, thereby providing the one or more control signals for implementing a cyclic independent pitch control of the blade without the predetermined phase shift.

In one or more embodiments, the providing the one or more control signals for implementing cyclic independent pitch control includes applying a coriolis transformation to the first and second pitch angle control output signals, and wherein the controller is configured to apply the predetermined phase shift to a phase shift input of the coriolis transformation, wherein the controller is configured to provide the one or more control signals for implementing cyclic independent pitch control of the blades of the wind turbine based on the first and second pitch angle control output signals and the phase shift input and a coriolis transformation of information indicative of a current azimuth angle of the wind rotor, so as to provide the one or more control signals for implementing cyclic independent pitch control with the predetermined phase shift.

Thus, in one or more examples, one or more control signals for implementing cyclic independent pitch control without a predetermined phase shift are provided by the controller by not applying the predetermined phase shift to the phase shift input of the coleman transform.

In one or more embodiments, the predetermined phase shift includes a phase shift between 120 degrees and 240 degrees. In one or more embodiments, the predetermined phase shift comprises a 180 degree phase shift. Thus, a phase shift may be applied with respect to the first pitch angle control signal and the second pitch angle control signal.

In one or more embodiments, the predetermined phase shift includes a function of the wind direction information.

In one or more embodiments, the controller is configured to:

receiving rapid wind direction change information indicating that a rapid wind direction change above a threshold level has occurred; and

Wherein the one or more control signals provided by the controller for implementing cyclic independent pitch control are conditioned on and responsive to a rapid change in the wind direction information indicating a rapid change in a wind direction event.

In one or more examples, the occurrence of the wind direction rapid change event is based on a wind direction change of greater than 30 degrees occurring in less than 30 seconds.

In one or more embodiments, the controller is configured to provide application of a coriolis transformation of the first and second pitch angle control output signals to provide the one or more control signals for cyclic independent pitch control of the blades of the wind turbine.

In one or more embodiments, the controller is configured to:

receiving a unified pitch reference angle indicating a current pitch angle of blades of the wind turbine;

The one or more control signals for enabling cyclic independent pitch control of the blades of the wind turbine are provided only when the uniform pitch reference angle indicates a pitch of the blades that are not stalled.

In one or more embodiments, the controller is configured to:

receiving a minimum uniform pitch angle indicative of a blade pitch angle at which blade stall is determined to occur;

determining whether the uniform pitch reference angle is greater than the minimum uniform pitch angle;

The one or more control signals for enabling cyclic independent pitch control of the blades of the wind turbine are provided only when the unified pitch reference angle is greater than the minimum unified pitch angle.

In one or more examples, the unified pitch reference angle includes an angle provided to the controller that indicates a blade pitch. In some examples, the pitch of the blade may be measured by a blade pitch sensor. If any one of the blades is at a different pitch angle than the other blades, the unified pitch reference angle may comprise an average of the pitch angles of the blades.

In one or more examples, the minimum uniform pitch angle includes a pitch angle at which it is determined that the wind turbine will extract power from wind at or above a higher power output level, which may be the determined optimal blade pitch.

In one or more embodiments, the controller is configured to:

receiving a minimum uniform pitch angle comprising determining a blade pitch angle at which blade stall occurs;

Calculating a maximum IPC pitch angle IPC _max based on a difference between the uniform pitch reference angle βcoll and a minimum uniform pitch angle β _opt, wherein:

IPC _max＝f(β_coll-β_opt), a function of β _coll-β_opt; and

Wherein the maximum IPC pitch angle indicates a maximum pitch angle deviation from the uniform pitch reference angle to avoid the blade stall; and wherein

The one or more control signals providing for achieving cyclic independent pitch control of the blades of the wind turbine are further based on the maximum IPC pitch angle.

In one or more examples, the providing of the one or more control signals for achieving cyclic independent pitch control is further based on the maximum IPC pitch angle being greater than zero.

In one or more embodiments, the controller is configured to:

Comparing the first pitch angle control signal with the maximum IPC pitch angle;

Comparing the second pitch angle control signal with the maximum IPC pitch angle;

wherein if the first pitch angle control signal is greater than the maximum IPC pitch angle, the first pitch angle control output signal is based on the maximum IPC pitch angle; and if the first pitch angle control signal is less than the maximum IPC pitch angle, the first pitch angle control output signal is based on the first pitch angle control signal; and

Wherein if the second pitch angle control signal is greater than the maximum IPC pitch angle, the second pitch angle control output signal is based on the maximum IPC pitch angle; and if the second pitch angle control signal is less than the maximum IPC pitch angle, the second pitch angle control output signal is based on the second pitch angle control signal.

In one or more embodiments, the determination of the first and second pitch angle control output signals is based on an average wind direction over a last period of time derived from the wind direction information.

In one or more examples, the controller is configured to determine the average wind direction by applying a low pass filter to wind direction information.

In one or more embodiments, the controller is configured to provide the predetermined phase shift and a second predetermined phase shift, referred to as a first predetermined phase shift, wherein the controller is configured to provide the one or more control signals for implementing cyclic IPC based on the first and second pitch angle control output signals and the first predetermined phase shift if the wind direction information indicates a wind direction incident on the first side of a wind turbine; and if the wind direction information indicates a wind direction incident on the second side of the wind turbine, the controller provides the one or more control signals for implementing cycle IPC without the first predetermined phase shift but with the second predetermined phase shift based on the first pitch angle control output signal and the second pitch angle control output signal.

According to a second aspect of the present disclosure we provide a wind turbine comprising the controller of the first aspect.

According to a third aspect of the present disclosure we provide a method for providing cyclic independent pitch control of blades of a wind turbine, the method comprising:

According to a fourth aspect of the present disclosure we provide a computer program product comprising computer program code configured to provide the method of the third aspect when executed by a processor having a memory.

According to a first aspect of the invention we provide a controller for controlling a wind turbine having a tower and a rotor comprising a plurality of blades, and wherein the rotor is coupled to a generator, wherein the pitch of the blades is controllable and the torque applied to the rotor by the generator is controllable, wherein the controller is configured to: providing a first shutdown mode, wherein the controller is configured to provide one or more first shutdown control signals to provide one or both of (a) a change in blade pitch of one or more of the plurality of blades to slow down the wind rotor and (b) a change in torque applied to the wind rotor by the generator to slow down the wind rotor; And providing a second shutdown mode different from the first shutdown mode, wherein the controller is configured to provide one or more second shutdown control signals to provide one or both of (a) a change in blade pitch of one or more of the plurality of blades to slow down the rotor and (b) a change in torque applied to the rotor by the generator to slow down the rotor; wherein the one or more second shutdown control signals are configured to decelerate the wind turbine at a faster rate than the one or more first shutdown control signals at least over a predetermined range of rotational speeds, wherein the predetermined range of rotational speeds is defined to include at least one rotational speed corresponding to a resonant frequency of one or more of the wind turbine, tower, or blades; And wherein the controller is configured to: receiving a shutdown request, the shutdown request comprising a request to reduce the rotational speed of the rotor to at least a predetermined minimum rotor rotational speed; wherein the second shutdown mode is provided instead of the first shutdown mode based on receiving rapid wind direction change information indicating that a rapid change in wind direction above a threshold level has occurred. In one or more embodiments, the controller may be configured to provide the first shutdown mode in response to receiving a shutdown request and without rapid wind direction change information indicating that a rapid change in wind direction above a threshold level has occurred. Thus, one or more components of the wind turbine, such as the tower and blades, may have respective resonant frequencies that may be excited by one or more specific rotational speeds or equivalent rotational speeds of the wind turbine. By resonant frequency we mean a vibration mode comprising a tower or blade or rotor occurring at a particular frequency. At different rotational speeds or frequencies, different vibration modes may be excited in the one or more components of the wind turbine. When the wind direction changes rapidly, damping of vibrations caused by wind flow at these resonant frequencies may be reduced, and thus providing a second shutdown mode may be advantageous in mitigating the effects of the wind wheel moving past undamped (including less damped) resonant frequencies during shutdown, which will be converted at a faster rate in the second shutdown mode. In one or more embodiments, the predetermined range of rotational speeds may include rotational speeds corresponding to one or more of the following resonant frequencies: (a) a uniform excitation frequency in the first swing direction; (b) An excitation frequency associated with the back-and-forth oscillations of the tower; (c) an excitation frequency associated with lateral oscillations of the tower; (d) Blade flapping frequency of one or more of the plurality of blades; (e) A uniform flapping frequency for all of the plurality of blades; (f) A uniform shimmy frequency for all of the plurality of blades; (g) forward and backward rotational flapping frequency; (h) a shimmy frequency of forward and backward rotation; (i) tower torsion excitation frequency; and (j) blade torsional excitation frequency. In one or more examples, the predetermined range of rotational speeds includes rotational speeds corresponding to combinations of the flap frequencies. In one or more embodiments, the predetermined range of rotational speeds may include rotational speeds at least one of 1P and 2P, 3P, 4P, 6P, and 9P, where P represents the rotational speed of the rotor, corresponding to one or more of: (a) a uniform excitation frequency in the first swing direction; (b) An excitation frequency associated with the back-and-forth oscillations of the tower; (c) Blade flapping frequency of one or more of the plurality of blades; (d) A uniform flapping frequency for all of the plurality of blades; and (e) a flapping frequency of forward and backward rotation. In one or more examples, the flapping frequencies tend to provide destructive oscillations when not damped by wind flow, and thus by defining a predetermined range of rotational speeds based on these frequencies, the controller may mitigate this effect by decelerating the rotor by decelerating faster within the predetermined range of rotational speeds. In one or more embodiments, the predetermined range of rotational speeds may be between a lower rotational speed and a higher rotational speed, wherein: the higher rotational speed is defined by a resonant frequency of one or more of the rotor, tower, or blades plus a rotational speed corresponding to a first threshold amount; And/or the lower rotational speed is defined by the resonant frequency of one or more of the rotor, tower or blades minus a rotational speed corresponding to a second threshold amount. In one or more embodiments, the one or more second shutdown control signals may provide for application of a greater generator torque than the one or more first shutdown control signals to slow down the rotor, at least at a predetermined range of rotational speeds corresponding to the rotational speeds. In one or more examples, the application of the greater generator torque is provided by the one or more second shutdown control signals configured to (a) increase the torque applied by the generator by causing an increase in voltage across one or more coils of the generator, and (b) increase the power output of the generator. In one or more embodiments, the controller may be configured to perform a generator torque limit defining a maximum torque that one or more first shutdown control signals cause the generator to apply to the wind rotor during a first shutdown mode, wherein the controller is configured to provide the one or more second shutdown control signals cause the generator to apply a torque that is greater than the generator torque limit during a second shutdown mode, thereby exceeding the generator torque limit. In one or more embodiments, the controller may be configured to provide the one or more second shutdown control signals such that they cause the pitch of the plurality of blades to change toward feathered blade orientation during the second shutdown mode when the generator applies a torque greater than the generator torque limit. In one or more embodiments, the controller may be configured to receive blade pitch limit information defining a temporary limit on blade pitch at a point in time, wherein the one or more second shutdown control signals are configured to change the pitch of the plurality of blades towards the feathered blade orientation without exceeding the temporary limit on blade pitch, wherein the blade pitch limit information may be determined by the controller to mitigate negative thrust exerted on the wind turbine, wherein the negative thrust acts in a direction in which the wind turbine is pointed to push the wind turbine. In one or more embodiments, the controller may be configured to receive rotational speed information indicative of a rotational speed of the wind rotor, and in a second shutdown mode, the second shutdown control signal is configured to: when the rotational speed of the wind wheel is greater than a low wind wheel rotational speed threshold, causing the blades to pitch toward feathering at a first pitch rate at least within a threshold of a maximum pitch rate of the blades; And when the rotational speed of the rotor is less than a low rotor rotational speed threshold, orienting the blades toward feathering at a second pitch rate that is less than the first pitch rate. In one or more embodiments, the second pitch rate may comprise a constant pitch rate. In one or more embodiments, the controller may be configured to receive blade pitch limit information defining a temporary limit on blade pitch at a point in time, and wherein the second pitch rate comprises a constant pitch rate at least when a change in blade pitch at the second pitch rate is unaffected by the temporary limit defined by the blade pitch limit information. In one or more embodiments, the controller may be configured to determine, during the providing of the second shutdown control signal, whether the blade pitch is at a predetermined pitch angle, and when the predetermined pitch angle is reached, increase the blade pitch rate to orient the blades toward feathering at a rate that is greater than the second pitch rate. In one or more embodiments, the controller may be configured to receive acceleration information indicative of acceleration experienced by one or both of a tower and nacelle of the wind turbine, and during provision of the second shutdown mode; the controller is configured to provide the one or more second shutdown control signals such that they cause a change in pitch of the plurality of blades toward a feathered blade orientation; Wherein the pitch rate oriented toward the feathered blades is increased based on acceleration information indicative of vibrations above a first threshold vibration level; and wherein the pitch rate oriented towards the feathered blades is reduced based on acceleration information indicative of vibrations below a second threshold vibration level which is lower than the first threshold vibration level. In one or more examples, the increase in pitch rate is an increase to within a maximum pitch rate threshold of the blade, the maximum pitch rate defining a maximum rate at which the blade pitch can be changed. In one or more examples, the decrease in pitch rate is a decrease to a predetermined pitch rate. In one or more embodiments, the predetermined minimum rotor speed may include less than 0.3 radians/second. In one or more embodiments, the predetermined minimum rotor speed may comprise less than 25% of a rated speed of the wind turbine, wherein the rated speed comprises the predetermined value. In one or more embodiments, the controller may be configured to: the one or more first shutdown control signals provided during the first shutdown mode are configured to provide a generator disconnection process in which the torque applied by the generator to the wind rotor is reduced to within a torque threshold of zero torque before the generator is disconnected from the grid-connected power converter of the wind turbine; and the one or more second shutdown control signals provided during the second shutdown mode are configured to disconnect the generator from the grid-tied power converter when the torque applied by the generator is greater than the torque threshold. This may be advantageous because the generator disconnection process may take time and while it may minimize stress on the generator, it does not allow for a quick stop of the wind turbine. Thus, allowing the generator to be disconnected at torque levels above zero, the second shutdown mode may be completed faster. In one or more examples, the rapid change in wind direction above a threshold level may include a change in wind direction of greater than 30 degrees occurring over a period of up to 30 seconds. According to a second further aspect of the invention we provide a wind turbine comprising the controller of the first further aspect. According to a third aspect of the present invention we provide a method for controlling a wind turbine having a tower and a rotor comprising a plurality of blades, and wherein the rotor is coupled to a generator, wherein the pitch of the blades is controllable and the torque applied to the rotor by the generator is controllable, wherein the method comprises: receiving a shutdown request, the shutdown request comprising a request to reduce the rotational speed of the rotor to at least a predetermined minimum rotor rotational speed; Receiving rapid wind direction change information indicating the occurrence of rapid changes in wind direction above a threshold level; providing a second shutdown mode instead of the first shutdown mode based on receiving rapid wind direction change information indicating that a rapid change in wind direction above a threshold level occurs when a shutdown request is received; wherein the first shutdown mode includes providing one or more first shutdown control signals to provide one or both of (a) a change in blade pitch of one or more of the plurality of blades to slow down the wind rotor and (b) a change in torque applied to the wind rotor by the generator to slow down the wind rotor; and the second shutdown mode is different from the first shutdown mode and includes providing one or more second shutdown signals to provide one or both of (a) a change in blade pitch of one or more of the plurality of blades to slow the rotor and (b) a change in torque applied to the rotor by the generator to slow the rotor; Wherein the one or more second shutdown control signals are configured to decelerate the wind turbine at a faster rate than the one or more first shutdown control signals at least within a predetermined range of rotational speeds, wherein the predetermined range of rotational speeds is defined to include at least one rotational speed corresponding to a resonant frequency of one or more of the wind turbine, tower, or blades. According to a fourth aspect of the invention we provide a computer program product comprising computer program code configured to provide the method of the third further aspect when executed by a processor having a memory.

According to a first further aspect of the invention we provide a controller for controlling a wind turbine having a rotor comprising two or more blades, wherein the pitch of the blades is controllable, and wherein the controller is configured to: receiving wind speed information indicating a wind speed at a wind turbine; receiving rotation speed information indicating the rotation speed of the wind wheel; determining a minimum thrust coefficient C _t-min comprising a thrust coefficient providing a predetermined minimum thrust on the wind turbine, the minimum thrust coefficient comprising a function of wind speed based on the received wind speed information, air density based on the received air density information, a predetermined value indicative of a swept area of the wind rotor of the wind turbine and the predetermined minimum thrust; and determining a maximum pitch angle β _max based on the minimum thrust coefficient C _t-min, the wind speed information, and the rotational speed information; and wherein the controller is configured to provide one or more control signals to control the blade pitch of two or more blades of the wind turbine to a controlled blade pitch, and wherein the controller is configured to ensure that the controlled blade pitch does not exceed the maximum pitch angle. Thus, in one or more examples, the thrust limit defines a minimum thrust on the wind turbine that the controller attempts to maintain by controlling blade pitch using the maximum pitch angle. The predetermined minimum thrust may be a predetermined positive thrust. The predetermined minimum thrust may include a negative thrust within a predetermined negative thrust threshold of zero thrust. The magnitude of the thrust force may be defined relative to the maximum expected thrust force under normal operating conditions. For example, the predetermined minimum thrust may be between 10% and-10% of the expected maximum thrust expected to be applied by wind to the wind turbine during normal operation. In other embodiments, the predetermined minimum thrust may be between 5% and-5%, between 3% and-3%, or between 1% and-1% of the expected maximum thrust expected to be applied by wind to the wind turbine during normal operation. In one or more embodiments, the controller configured to determine the minimum thrust coefficient includes a controller configured to determine the minimum thrust factor C _t-min based on an equation:

where V comprises wind speed based on the received wind speed information, ρ comprises air density based on the received air density information, A comprises a predetermined value indicative of swept area, and F _thrust-limit comprises a predetermined minimum thrust. However, typically the minimum thrust coefficient may comprise a function of the predetermined minimum thrust divided by the square of the wind speed. In one or more embodiments, the controller is configured to determine the maximum pitch angle β _max by referencing a predetermined look-up table that provides values of the maximum pitch angle β _max for each value of the rotational speed, wind speed, and minimum thrust coefficient C _t-min. In one or more embodiments, the controller is configured to determine a maximum pitch angle and provide the one or more control signals without exceeding the maximum pitch angle in response to a rapid change in wind direction occurring above a threshold level. Thus, in one or more examples, one or more thresholds define a threshold level, thereby defining when a change in wind direction is considered rapid. Further, the load on the wind turbine during such an event may define when a threshold level has been exceeded, thereby determining when to provide a control action. In one or more examples, the controller is configured to provide the one or more control signals without exceeding the maximum pitch angle for at least a predetermined period of time after a rapid change in the wind direction above a threshold level, and after expiration of the predetermined period of time, the controller may be configured to provide the one or more control signals without limiting them to a maximum pitch angle. In one or more embodiments, the controller is configured to dynamically determine the predetermined minimum thrust as a function of thrust experienced by the wind turbine during a recent time period. In one or more embodiments, the controller is configured to dynamically determine the predetermined minimum thrust as a function of thrust experienced by the wind turbine during a recent time period and before rapid changes in wind direction above a threshold level occur during the recent time period. In one or more embodiments, the function of thrust includes an appropriate fraction of thrust experienced by the wind turbine during the most recent time period between-0.1 and 0.75. In one or more embodiments, the controller is configured to determine the current thrust force F _t based on an equation:

Where v comprises wind speed from wind speed information, β comprises current blade pitch, ρ comprises air density based on air density information, Ω comprises rotational speed of the rotor from rotational speed information, and a comprises a predetermined value indicative of a swept area of the rotor of the wind turbine; and in response to receiving an indication of a rapid change in wind direction above a threshold level, determining the predetermined minimum thrust as an appropriate fraction of the current thrust F _t determined during the recent period of time. Thus, in one or more examples, the current thrust at which the wind direction changes rapidly may be used. in other examples, a current thrust of 5, 10, 15, or 20 seconds before the wind direction changes rapidly may be used. The controller may be configured to buffer in a buffer a most recent calculation of said current thrust. In one or more embodiments, in the determination of the minimum thrust coefficient C _t-min, the wind speed based on the received wind speed information includes an average wind speed over a recent period of time. In one or more embodiments, the controller is configured to determine the maximum pitch angle β _max based on an average wind speed over a second most recent period of time based on the wind speed information. In one or more examples, the average wind speed is determined by low pass filtering the wind speed information. In one or more examples, the second most recent time period may be different from the most recent time period used in determining the minimum thrust force. In one or more embodiments, the controller is configured to determine the maximum pitch angle β _max based on an average rotational speed of the wind wheel over a third most recent period of time based on rotational speed information. In one or more examples, the average rotational speed is determined by low pass filtering the rotational speed information. In one or more embodiments, the controller is configured to limit the controlled blade pitch to the determined maximum blade pitch angle if the controlled blade pitch is greater than the determined maximum pitch angle. According to a second further aspect of the invention we provide a wind turbine comprising the controller of the first further aspect, wherein the pitch of the blades of the wind turbine is limited by the maximum pitch angle. According to a third aspect of the invention we provide a method of controlling a wind turbine having a rotor comprising two or more blades, wherein the pitch of the blades is controllable, and wherein the method comprises: receiving wind speed information indicating a wind speed at a wind turbine; Receiving rotation speed information indicating the rotation speed of the wind wheel; determining a minimum thrust coefficient C _t-min comprising a thrust coefficient providing a predetermined minimum thrust on the wind turbine, the minimum thrust coefficient comprising a function of a wind speed based on the received wind speed information, an air density based on the air density information, a predetermined value indicative of a swept area of a wind rotor of the wind turbine and the predetermined minimum thrust; determining a maximum pitch angle beta _max based on the minimum thrust coefficient C _t-min, the wind speed information, and the rotational speed information, and providing one or more control signals to control blade pitching of two or more blades of the wind turbine without exceeding the maximum pitch angle. According to a fourth aspect of the present invention we provide a computer program or computer program product comprising computer program code configured to provide the method of the third further aspect when executed by a processor having a memory.

Drawings

Embodiments of the invention will now be described in detail, by way of example only, with reference to the following drawings, in which:

FIG. 1 illustrates a side view of an example wind turbine and controller;

FIG. 2 illustrates a front view of the example wind turbine and controller of FIG. 1;

FIG. 3 illustrates an example controller that may be provided in conjunction with one or more sensors;

FIG. 4 shows an example flow chart illustrating an overview of a control scheme for detecting wind direction changes above a threshold level and contributing to said detection;

FIG. 5 shows an example functional block diagram illustrating an embodiment of the functionality of a control action for cyclic independent blade pitch control provided by a controller according to a first example embodiment;

FIG. 6 shows an example functional block diagram illustrating a second embodiment of the functionality of a control action for cyclic independent blade pitch control provided by a controller according to the second example embodiment;

FIG. 7 illustrates a flow chart of an example method of providing control actions for cyclical independent blade control;

FIG. 8 shows a schematic diagram illustrating the concepts of positive and negative thrust for a wind turbine;

FIG. 9 shows an example functional block diagram illustrating an embodiment of the functionality of a control action for negative thrust mitigation provided by a controller according to a second example embodiment;

FIG. 10 shows a flowchart illustrating an example method of providing control measures for negative thrust mitigation;

FIG. 11 shows an example graph illustrating the effect of negative thrust reducing control brakes that a controller may instruct a blade to employ on blade pitching;

FIG. 12 shows an example plot of lateral position derived from acceleration information measured by an acceleration sensor configured to measure lateral acceleration experienced by a tower relative to a long-term average over a period of time;

FIG. 13 shows a resonant frequency plot;

FIG. 14 illustrates an example controller for decelerating a wind turbine according to two or more different shutdown modes;

FIG. 15 illustrates a flow chart of an example method of providing different shutdown modes; and

FIG. 16 illustrates an example computer-readable medium.

Detailed Description

Example fig. 1 and 2 show side and front views of an example wind turbine 100 and a controller 101 for the wind turbine. The wind turbine 100 includes a tower 102 and a rotor 103, the rotor 103 being operatively coupled to a generator 104 mounted within a nacelle 105. The controller 101 is shown schematically within the base of the tower 102, but in other examples it may be mounted elsewhere. The wind rotor 103 may be coupled with the generator 104 via a gearbox 106, the gearbox 106 also being mounted within the nacelle 104. The main bearings (not visible in fig. 1) support the rotor 103 and allow it to rotate. Wind turbine 103 includes a hub 107 and three blades 108A, 108B, and 108C (shown collectively as 108 in FIG. 1) extending from hub 107. Although this example wind turbine 100 has three blades, other numbers of blades are possible, such as two or more blades. Each blade is operatively connected to the hub 107 by a blade bearing that allows the blade to rotate relative to the hub such that the pitch (i.e., rotation about the longitudinal axis) of each blade is adjustable. The generator 104 and optional gearbox 105 are controllable and may be controlled during operation to effectively extract energy from the wind. The generator 104 and optional gearbox 105 are also controllable so that torque can be applied to the rotor 103, which torque can be used to control its rotational speed.

In one or more examples, the pitch of blades 108A, 108B, 108C may be controlled jointly or independently. Thus, each blade 108A, 108B, 108C may be rotatably mounted to the hub 107 and coupled with an actuator to control the pitch of the blade. Accordingly, the controller 101 may be configured to provide one or more control signals to control the actuators to change the pitch of one or more blades of the wind rotor. In one or more examples, the controller may be configured to collectively change the pitch of the blades 108A, 108B, 108C. Thus, the pitch of each blade is changed to the same pitch. In other examples, the controller may be configured to independently change the pitch of the blades 108A, 108B, 108C such that at least one blade has a different pitch relative to the other blades.

In example fig. 3, the controller is also shown separate from the wind turbines 100 it controls. Controller 101 is operably coupled to receive information from inputs 301-304, such as from one or more sensors associated with wind turbine 100 and optionally mounted on wind turbine 100. The controller 101 is configured to transmit one or more control signals to the components of the wind turbine at one or more outputs 305, 306. The information received by the controller at one or more of its inputs 301 to 304 may vary depending on the function it is configured to provide. However, examples of multiple sensors or other processing modules that may be configured to provide information to the controller 101 at an input are described.

The one or more sensors may include one or more of a wind speed sensor 307, a wind direction sensor 308, and a rotational speed sensor 309. The wind speed sensor 307 is configured to measure the current wind speed experienced by the wind turbine. The wind speed sensor is typically mounted on the wind turbine 100, and the nacelle 105 behind the rotor 103 may be separate therefrom, mounted in the wind farm in which the wind turbine is located. In other examples, a laser radar (LIDAR) based sensor may be used. It will be appreciated that the wind speed sensor may comprise one or more sensors from which the wind speed may be derived, whether by direct measurement of the wind speed or inferred from one or more other measured variables. For example, the wind speed sensor may be embodied as a wind speed estimator that determines or estimates a wind speed based on a rotor speed, a generated power, and a pitch angle. Alternatively, a tip speed sensor, such as a guide tube, may be used, which is then used to calculate the tip speed ratio, and from which the wind speed may be derived. Accordingly, the controller 101 may be configured to receive wind speed information from the wind speed sensor in any form at the input 301.

The wind direction sensor 308 may include a wind vane mounted to the nacelle 105. In other examples, the wind direction sensor may include a lidar-based sensor. Accordingly, controller 101 may be configured to receive wind direction information from the wind direction sensor in any form at input 302. It should be appreciated that wind direction sensor 308 may be mounted on the wind turbine or may be separate from the wind turbine and located in the wind farm that will be incident on the wind turbine. It should be appreciated that the wind direction sensor may comprise one or more sensors from which the wind direction may be derived, whether by directly measuring the wind direction or inferred from one or more other measured variables.

The rotational speed sensor 309 is configured to measure the rotational speed of the rotor 103. Again, it should be understood that the rotational speed sensor may comprise one or more sensors from which rotational speed may be derived, whether by direct measurement of rotational speed or inferred from one or more other measured variables. For example, a generator speed sensor may be used, which is then used to calculate the rotor speed using a predetermined knowledge of the gear ratio between the rotor and the generator. Or the position sensor may detect the blade position and then use it to calculate the rotor speed. Alternatively, a centripetal force sensor may be used, which is then used to calculate the rotor speed. Alternatively, a tip speed sensor, such as a guide tube, may be used, which is then used to calculate the tip speed ratio, and the rotational speed may be determined therefrom. Or vibration sensors, such as accelerometers, may estimate rotor speed based on vibration patterns observed in the tower or blades. Alternatively, the blade load sensor may determine the load on the blade and, from predetermined information about the relationship of the load and the rotor speed in terms of centripetal force or vibration, the rotor speed may be derived. In other examples, GPS data from a GPS receiver may be used to determine tower motion and derive rotor speed. Accordingly, the controller 101 may be configured to receive rotational speed information from the rotational speed sensor in any form at the input 303.

While the above description provides examples of receiving information from the sensor, it should be understood that the same information may be received via a signal processing module that may be configured to process the information prior to receipt by the controller 101. Thus, the information may be filtered, digitally sampled, denoised, and/or averaged before it reaches inputs 301 to 304.

The controller 101 may receive information from other sensors or other control processes at input 304. Accordingly, block 310 represents one or more other sensors or other signal processing modules or other controllers from which information required by the controller 101 may be received.

The controller 101 may be configured to control the generator 104, in particular to control the torque applied to the rotor 103, by providing one or more control signals as at the first output 305. The controller 101 may be configured to control the pitch of each of the plurality of blades 108A-C by providing one or more control signals as at the second output 306. It should be appreciated that the controller 101 may be configured to provide one or more other control signals, such as applying braking forces through the wheel brakes or making changes to gears in the gearbox 106. The control signals may be provided at separate outputs, as shown in fig. 3, or may be provided at a single output. Wherein control signals are sent to the components they control.

Wind turbine 100 may experience rapid changes in wind direction and/or wind speed, where these rapid changes cause undesirable loads on components of the wind turbine (e.g., the main bearings). The following examples relate to the operation of the controller 101 and, in particular, to control actions that the controller may provide in response to detecting wind direction changes that may exceed a predetermined threshold, and optionally, to control measures that the controller may provide in response to detecting wind speed and wind direction changes that may exceed a predetermined threshold. Thus, the predetermined threshold may define what is a rapid or "extreme" change in wind direction and/or wind speed event, which may be determined to cause undesirable damage, vibration, or fatigue to the wind turbine. The controller 101 may use detection of such a change above a threshold to trigger a control action to manage operation of the wind turbine 100 during or in response to such an event. However, beyond rapid or "extreme" changes in wind direction and/or wind speed events, control actions may be beneficial. The control actions may include issuing one or more control signals at outputs 305, 306 for controlling one or both of generator torque and blade pitch.

Rapid changes in wind direction and/or wind speed events that cause controller 101 to issue control actions may vary from wind turbine to wind turbine. However, for example, wind direction changes of greater than 30 degrees occurring in less than 30 seconds may be considered rapid changes in wind direction and trigger a control action. Thus, the operation of the controller 101 may be calibrated to identify when such a change occurs. In other examples, the operation of the controller 101 may be calibrated to identify extreme changes in wind direction and/or wind speed as defined in the IEC 61400 standard (IEC STANDARD 61400).

Example fig. 4 shows a flow chart illustrating a method that the controller 101 may follow to mitigate the effects of rapid changes in wind direction.

Block 401 represents the start of the method. Block 402 illustrates providing a control algorithm that detects at least the occurrence of wind direction changes above a threshold level. As known to those skilled in the art, wind direction changes that occur above a threshold level may be referred to as "rapid change of direction" events or "ECD" events (representing extreme changes in direction). How the controller 101 is specifically configured to provide the function of block 402 is not of importance here, but may generally be considered to involve a comparison of information indicative of a change in wind direction with a threshold value, and if the threshold value is exceeded, the controller considers that a rapid change event in wind direction has occurred.

If a rapid change of direction event or ECD event is detected, the method proceeds to block 403, referred to as a "safe mode", where control actions are taken to mitigate the effects of the "rapid change of direction" event or ECD event in block 403. The functionality of the controller 101 described in the embodiments below may be provided as part of block 403.

If a rapid change of direction event or ECD event is not detected at block 402, the method proceeds to block 404 where the controller 101 determines if a high yaw error is present. Yaw error may be determined by calculating a difference between wind turbine orientation and wind direction. The wind turbine orientation may be defined, for example, by the position or orientation of the nacelle. Thus, if the rotor is facing the wind direction, the yaw error may be 0 degrees. If the wind direction is incident from the right side, the yaw error may be +90 degrees. If the wind is incident from the left, the yaw error may be-90 degrees. In general, a high yaw error may be determined by comparing the yaw error to a high yaw error threshold. The method may also proceed to block 403 if a high yaw error is detected. If a high yaw error is not detected in this example, the method ends at 405 and resumes at block 401.

In some examples, the "safe mode" of block 403 also includes checking various conditions to determine whether the wind turbine is to be shut down (i.e., the turbine speed is reduced, such as stopped). If various "shutdown" conditions are met, the method may proceed to block 406 where the unit is shut down. Once the unit is shut down, the method reaches block 407. Block 407 shows the step of controlling the yaw of the unit such that it points in the current wind direction. Block 408 illustrates a restart of the wind turbine. The method then proceeds to step 401. It should be appreciated that the method shown in fig. 4 focuses on detecting a fast changing event of direction or ECD event and providing control actions, however, various other control actions may be provided in parallel.

A number of control actions will now be described. The controller 101 may be configured to provide one or more, two or more, or three of the plurality of control actions. In some examples, two or more of the plurality of control actions may be provided in parallel, i.e. simultaneously, with another control action for the wind turbine.

Control actions of cyclic independent vane control

In this example, the pitch of blades 108A, 108B, 108C may be controlled individually. Thus, each blade 108A, 108B, 108C may be rotatably mounted to the hub 107 and coupled with an actuator to control the pitch of the blade. Accordingly, the controller 101 may be configured to provide one or more control signals to control the actuators to change the pitch of one or more blades of the wind rotor.

Those skilled in the art of wind turbine control will appreciate that in one or more examples, it may be desirable to control the pitch angles of the blades such that the pitch angle of one of blades 108 is different from the pitch angle of the other blade or blades. Accordingly, the controller may be configured to provide independent pitch control (Individual Pitch Control, IPC) by controlling the pitch angles of the blades such that the pitch angle of at least one blade differs from the pitch angles of the other blades at least some time during full rotation of the rotor 103.

In one or more examples, the controller may be configured to provide cyclic independent pitch control, i.e., cyclic IPC, which includes one type of independent pitch control. In providing the cyclical IPC, the controller is configured to control the instantaneous pitch angle of each blade as a function of the instantaneous rotation angle of the respective blade relative to an assumed (notional fixed) reference angle. The function of each blade is typically the same or at least substantially the same. Thus, the controller will pitch each blade through substantially the same sequence of pitch angles during a complete rotation of the rotor, depending on the rotation angle of the respective blade with respect to the same assumed reference angle.

The functions provided by the controller 101 in providing cyclical IPC will now be described with reference to the example functional block diagram of fig. 5. It should be appreciated that the example functional block diagram illustrates functionality provided by the controller for implementing cyclical IPC, and that the controller 101 may be configured to provide other control actions, which may include control actions provided simultaneously. The functionality shown here may be provided by a programmable logic controller. Or the filters and/or amplifiers may comprise discrete signal processing components. In another embodiment, the controller may provide a software-based implementation of the functionality shown. Combinations of the above embodiments are also within the scope of the present disclosure.

In one or more examples, the controller is configured to receive a uniform pitch reference angle β _coll at an input 501. Thus, referring to the controller 101 shown in fig. 3, a unified pitch reference angle may be received at input 304. The unified pitch reference angle represents the current pitch angle of the wind turbine blades. In this example, the unified pitch reference angle includes an angle provided to the controller 101.

The pitch of the blades may be measured by one or more blade pitch sensors to provide a uniform pitch reference angle to the controller 101. In other examples, it should be appreciated that the controller 101 may actively control the pitch of the blade by issuing one or more control signals to the blade pitch actuators as part of different control actions, and the uniform pitch reference angle may be based on these control signals, i.e., the controller instructs the blade to adopt the blade pitch. If any one of the blades is at a different pitch angle than the other blades, the unified pitch reference angle may comprise an average of the pitch angles of the blades. The uniform pitch reference angle may comprise the current instantaneous pitch angle of the blade, or in other embodiments, its nearest average.

The pitch angle of a blade may be measured as the angle of rotation between the fixed and rotatable parts of the blade bearing. It should be appreciated that the 0 degree pitch angle reference may be freely selected, but in one or more embodiments, the 0 degree pitch angle reference may be defined as the pitch angle at which optimal power extraction may be achieved. Thus, in examples herein, a high forward blade pitch angle (e.g., about +90 degrees) may indicate that the blade is in a feathered orientation, and thus the angle of attack may be oriented at about 90 degrees relative to the direction of rotation. The zero degree blade pitch angle brings the angle of attack closer to the direction of rotation and the blade may be in a fine orientation. The pitch angle may take a positive or negative value and may be in the range of, for example, -90 to 120 degrees, -30 to 100 degrees, -5 to 90 degrees or any other angle.

Further, in one or more examples, controller 101 is configured to receive minimum uniform pitch angle β _opt at input 502. The minimum unified pitch angle indicates a blade pitch angle at which blade stall is determined to occur. Blade stall is a concept familiar to those skilled in the art, and it should be appreciated that determining the angle of a particular blade stall can be calculated in a variety of ways. For example, the minimum uniform pitch angle may be a uniform pitch angle for which the gradient of the wind turbine efficiency power coefficient curve is negative. In yet another example, the minimum uniform pitch angle may be a collective pitch angle of more than x% of the blade cross-sections of the blade stall, where x may be defined as an acceptable limit. However, in general, with the present controller, the minimum uniform pitch angle is the minimum pitch angle for the purpose of providing cyclic IPC. Thus, referring to the controller 101 shown in FIG. 3, a minimum unified pitch angle may be received at input 304. In one or more examples, the minimum uniform pitch angle is equivalent to the power optimal blade pitch reference angle. The minimum uniform pitch angle (or the optimal blade pitch reference angle) may be determined by the controller 101 or another controller. How to calculate the minimum uniform pitch angle will be known to the person skilled in the art. However, in one or more examples, the minimum uniform pitch angle may be determined by a process of the controller and may be based on a model that may be used to predict the blade stall angle. In one or more examples, the minimum uniform pitch angle may include an error margin, and thus the minimum uniform pitch angle may include a pitch angle having a stall probability at a predetermined level less than 100%.

The power optimal pitch angle includes a blade pitch angle at which it is determined that power that wind turbine 100 will extract from the wind will reach or exceed a high power output level (upper-power_output-level). In some examples, this may be an optimal power level, or the high power output level may be a function of the optimal power level, such as defining the high power output level as a level within a threshold of the optimal power level. The power-optimal pitch angle may be received from another process provided by the controller that determines the power-optimal pitch angle. The power optimal pitch angle may comprise a function of the effective wind speed, including a wind speed component incident perpendicular to the plane of wind wheel 103. Thus, the effective wind speed v _eff may be determined by v _eff＝v_measured cos γ, where v _measured comprises the measured wind speed, such as from a wind speed sensor or more generally from wind speed information provided to the controller, and γ comprises an angle indicative of the current orientation of the wind rotor 103 relative to the measured wind direction, commonly referred to in the art as yaw error. In one or more examples:

Wherein C _p(β,v_eff, Ω) comprises a thrust coefficient that is a function of the blade pitch angle β, the rotational speed Ω of the rotor, and the effective wind speed v _eff as described above.

Further, in one or more examples, controller 101 is configured to receive wind direction information as from a wind direction sensor at input 503. The controller 101 may be configured to determine a moving average (moving average) of wind direction over a recent period of time (e.g., over the last three seconds) from the wind direction information received at the input 503. In other examples, the most recent time period may include at most or at least one second, two seconds, three seconds, four seconds, five seconds, six seconds, seven seconds, eight seconds, nine seconds, or ten seconds. In one or more examples, the controller may be configured to filter the wind direction information using a low pass filter 504, which may in fact provide the most recent average wind direction, rather than using a moving average. The time constant of the low pass filter may be configured to define the most recent time period. In one or more examples, the time constant τ of the low pass filter is set to be between 1 and 4 seconds, for example 3 seconds.

The controller 101 may be configured to generate one or more control signals configured to provide a cyclic IPC. In this example, the controller 101 is configured to modify or modulate one or more input control signals configured to provide a cyclic IPC. Thus, one or more input cycle IPC control signals may be determined by different processes, such as provided by controller 101 or different controllers, to control the pitch of the blades of each of blades 108A-C to provide cycle IPC, and the control signals may be received by controller 101. In some examples, the input cycle IPC control signal is predetermined and recalled from memory to define the pitch angle sequence.

In this example, the one or more input cycle IPC control signals include a first pitch angle control signal and a second pitch angle control signal. The first pitch angle control signal and the second pitch angle control signal comprise periodic signals defining a change in blade pitch of the plurality of blades during rotation of the rotor. In some examples, there may be a separate pitch angle control signal for each blade. Thus, in one or more examples, for a wind turbine having two blades, a first pitch angle control signal may be used to control a first of the two blades, and a second pitch angle control signal may be used to control a second of the two blades. In this example, the wind turbine has three blades, and in one or more examples, three respective pitch angle control signals may be provided, one for each blade.

However, in this example, the first pitch angle control signal includes a D component of a direct-to-quadrature-transform (DIRECT-quadrature-transform). The second pitch angle control signal comprises a Q component of the direct-to-quadrature axis transformation. The controller may be configured to receive a first pitch angle control signal at input 505. The controller may be configured to receive a second pitch angle control signal at input 506. The first pitch angle control signal may be understood as a change in blade pitch to induce a yaw moment in the rotor axis. The second pitch angle control signal may be understood as a change in blade pitch to introduce a tilting moment in the rotor axis. However, it will be appreciated that the first and second pitch angle control signals may be understood differently depending on how the direct-to-alternating-axis conversion is configured.

As known to those skilled in the art, the direct-to-quadrature axis transformation or DQ transformation is a common method for blade pitch control of blades 108 defining wind turbine 103 based on rotational angle. Thus, the D and Q components of the DQ conversion allow two control signals to provide control of the pitch of the three blades during the cycle IPC. Furthermore, as known to those skilled in the art, a Coleman transform may be used to receive the D and Q components and transform these values into a plurality of control signals, one for controlling the pitch of each of the blades 108A-C with reference to the current azimuth angle of the rotor.

In general, as will be described in more detail below, the controller 101 may be configured to provide one or more control signals for implementing cyclic independent pitch control of the blades of the wind turbine based on the first pitch angle control signal, the second pitch angle control signal, and (a) the uniform pitch reference angle and the minimum uniform pitch angle, and/or (b) wind direction information. The output of controller 101, i.e., the one or more control signals modulated by controller 101 to implement cyclic independent pitch control, may include the D and Q component signals provided at outputs 507 and 508, or the coleman transforms thereof provided at outputs 510, 511, 512.

It has been found how implementing cyclic IPC can have a significant impact, especially in variable wind farms. Thus, in one or more examples, the controller may be configured to apply the cyclic IPC control described herein based on the received wind direction rapid change information. As described above, the wind direction rapid change information indicates rapid changes in wind direction events above a threshold level. Thus, the control action provided by the controller 101 in this example may be conditioned on said wind direction rapid change information indicating that there is a rapid change in the wind direction event. Further, the controller may be configured to provide the control action in response to the occurrence of a rapid change, i.e., within a predetermined amount of time. However, in this example, the controller is configured to apply the cyclic IPC control described herein, irrespective of the wind direction rapid change information.

The controller 101 is configured to receive wind direction information at input 503. The controller may be configured to determine an average of wind direction information over a recent period of time by an optional low pass filter 504. The controller 101 is configured to modify the implementation of the cyclic independent pitch control based on the direction of incidence of the wind on the wind turbine with respect to the direction the rotor is facing.

In particular, the controller represented by the actions at block 515 is configured to determine whether wind is incident on a first side of the wind turbine or a second side of the wind turbine opposite the first side. In this example, the wind direction information represents yaw error. Yaw error may be determined by calculating the difference between wind turbine orientation (i.e., nacelle position) and wind direction. Thus, if the rotor is facing the wind direction, the yaw error may be 0 degrees. If the wind direction is incident from the right side, the yaw error may be +90 degrees. If the wind is incident from the left, the yaw error may be-90 degrees. It should be appreciated that the sign of the yaw error may be different such that in other examples, a negative number indicates the direction of the wind incident from the right side rather than the left side. Block 515 represents that the controller is configured to determine the sign of the yaw error and thus from which side of the wind turbine the wind is blowing.

Based on the wind being incident on the first side or the second side, the controller is configured to determine a first pitch angle control output signal (output FIRST PITCH ANGLE control signal) based on the first pitch angle control signal at block 516 and to determine a second pitch angle control output signal (output second PITCH ANGLE control signal) based on the second pitch control signal at block 517.

In particular, if the wind direction is determined to be incident on a first side (e.g., left side) of the wind turbine, the controller is configured to determine the first and second pitch angle control output signals by applying a predetermined phase shift to the first and second pitch angle control signals at blocks 516, 517, respectively.

Further, if the wind direction is determined to be incident on a second side (e.g., right side) of the wind turbine, the controller is configured to determine the first and second pitch angle control output signals without applying a predetermined phase shift to the first and second pitch angle control signals. Thus, the first pitch angle control signal may be unmodified in phase and provided as the first pitch angle control output signal. Likewise, the second pitch angle control signal may be unmodified in phase and provided as the second pitch angle control output signal.

Blocks 516 and 517 are thereby configured to selectively modify the phases of the first and second pitch angle control signals to form first and second pitch angle control output signals. By modifying the phase of the cyclic IPC to be applied, the inventors have found that in some examples the force applied to the main bearing can be reduced. It will be appreciated that the application of providing a phase shift when the wind direction comes from the first side is to reduce the moment on the main bearing during the cycle IPC. Likewise, it should be appreciated that the lack of phase shift applied when the wind direction is from the second side is to reduce or not increase the moment on the main bearing during the cyclic IPC.

Accordingly, the controller 101 is configured to provide one or more control signals, i.e. those at 507 and 508 or at 510-512, for implementing a cyclic independent pitch control of the blades of the wind turbine based on said first pitch angle control output signal and said second pitch angle control output signal.

In the present embodiment, the sign determined at block 515 is represented as +1 or-1 and the sign is multiplied with the first pitch angle control signal and the second pitch angle control signal at blocks 516, 517. Thus, if the sign at block 515 is positive, the first pitch angle control signal remains unchanged after multiplication by +1 to include the first pitch angle control output signal. Likewise, the second pitch angle control signal is multiplied by +1 and remains unchanged to include the second pitch angle control output signal.

If the sign at block 515 is negative, the first pitch angle control signal is multiplied by-1, effectively phase shifted 180 degrees, to include the first pitch angle control output signal. Likewise, the second pitch angle control signal is multiplied by-1, effectively phase shifted 180 degrees, to include the second pitch angle control output signal. Thus, in this example, the predetermined phase shift is 180 degrees. Thus, the blade pitch changes that occur during rotation of the rotor will be 180 degrees out of phase when the wind direction is on the second side of the wind turbine 100 compared to when the wind direction is on the first side of the wind turbine.

In this example, a 180 degree phase shift is applied to the cyclical IPC control signal, but in other examples the predetermined phase shift comprises a phase shift between 120 degrees and 240 degrees. In one or more examples, the predetermined phase shift includes a function of wind direction information. For example, the function may be formulated such that the amount of yaw moment depends on the magnitude of the wind direction change.

In one or more examples, the wind direction information is derived from one or more sensors, which may include wind direction sensors, such as wind vane-based or lidar-based sensors. In other examples, the one or more sensors may include an acceleration sensor. Accordingly, the controller may be configured to receive acceleration information indicative of the acceleration to which the tower and/or nacelle is subjected. The example of fig. 12 illustrates two traces 1201 and 1202 of acceleration information obtained from an acceleration sensor configured to measure lateral/side-to-side (side-to-side) acceleration experienced by a tower relative to a long-term average. Those skilled in the art will appreciate that the long-term average of the acceleration information provides a reference point, as it can be assumed that the tower will be subject to acceleration in all directions over a long period of time, and that the average of the acceleration information will be indicative of neutral (tower) acceleration. In other examples, the controller may be configured to determine the neutral position of the tower using a reference point determined in a different manner, such as from a position sensor. Trace 1201 shows acceleration information relative to average acceleration information when the wind direction is from the first side. Trace 1202 shows acceleration information relative to average acceleration information when the wind direction is from the second side. It can be easily understood that there is a strong correlation between the sign of the acceleration information with respect to the average acceleration information. It has been found that there are several effective methods for deriving wind direction from acceleration information. Thus, in summary, in one or more examples, we provide a controller configured to determine a side of a wind turbine on which wind is incident based on acceleration information indicative of lateral acceleration experienced by the wind turbine. In a first example, the controller may be configured to low pass filter the acceleration information at a frequency below the resonant frequency of the tower (e.g., below 0.5 of the resonant frequency of the tower), and integrate the acceleration information over time, then integrate the result further over time to obtain the displacement. It has been found that the direction of displacement is indicative of the direction of the wind, as the force of the wind on the wind turbine causes it to displace in the direction of the wind flow. In other examples, a notch filter tuned to the resonant frequency of the tower may be used instead of a low pass filter. In another example, the controller may be configured to provide tower lateral acceleration information to a summation block (cumulative sum block) such that the input of the block is trended over time to provide a reference point. The accumulation and block may be configured to provide a CUSUM (or accumulation and control charts) sequential analysis technique. Such accumulation and blocks may be used to determine whether the current acceleration information is positive or negative, and thus from which side of the wind turbine the wind is incident, while being robust to noise.

In this example, the controller is configured to provide an application of a Coleman transform to the first pitch angle control output signal 507 and the output second pitch angle signal 508 via block 518 to provide the cyclic independent pitch control of the blades of the wind turbine, as shown at 510-512. The Coleman (Coleman) transform block is configured to receive the zero pitch at input 513, around which the cyclic IPC pitch change is made. This value can be understood as a direct current component (DC component) input to the kalman conversion block. In this example, a zero value is provided at input 513. The kalman transform block is configured to receive a phase offset input at input 514. The value provided at input 513 controls the uniform pitch angle for the coleman transform, which value is set to exactly zero for this embodiment. When transforming the D and Q component signals into three control signals at outputs 510-512 for controlling each respective blade, the phase offset input at input 514 determines the phase offset imposed by the coleman transform. In this example, the phase shift input is not controlled because the phase shift is achieved by applying it to the D and Q components. However, in an alternative embodiment described later, the phase shift applied by block 515 may be applied to phase shift input 514.

The kalman transformation block 518 provided by the controller is further configured to receive the current azimuth of the rotor at input 528 based on azimuth information received from one or more sensors and/or azimuth derived from other information. As is familiar to those skilled in the art, the Coleman transform provides a transform at outputs 510-512 that converts the D and Q components into one or more control signals based on the phase offset input at 514 and the current azimuth angle received at 528.

We also disclose another embodiment wherein block 515 is configured to provide two different outputs of predetermined phase shifts; namely the above-mentioned predetermined phase shift (which may be referred to herein as a first predetermined phase shift) and a second predetermined phase shift. Thus, the controller is configured such that if the wind direction information indicates the wind direction incident on the first side of the wind turbine, it controls the output signals based on said first and second pitch angle and provides one or more control signals for implementing the cycle IPC with a first predetermined phase shift. Furthermore, if the wind direction information indicates a wind direction incident on a second side of the wind turbine, the controller provides one or more control signals for implementing the cycle IPC without a first predetermined phase shift but with a second predetermined phase shift based on the first and second pitch angle control output signals. Thus, in this example, the predetermined phase shift may be +90 degrees and the second predetermined phase shift may be-90 degrees. Thus, similar to the first embodiment, the cyclic IPC achieved by such an embodiment will be 180 degrees out of phase depending on which side of the wind turbine the wind direction is incident on. It should be appreciated that other values of the first predetermined phase shift and the second predetermined phase shift may be used.

Thus, in one or more examples, the controller 101 is configured to provide a conditional application of phase shift to the cyclical IPC control signal based on wind direction. The magnitude of the blade pitch change implemented as part of the present cyclical IPC control action will now be described. In some examples, only the phase control described above is provided, and in other examples, only the amplitude control described below is provided, and in other examples both will be provided.

The controller 101 receives a unified pitch reference angle indicating a current pitch angle of the blades of the wind turbine and is referred to herein as β _coll at 501. The controller 101 receives a minimum uniform pitch angle indicative of the blade pitch angle at which blade stall (determined by the different processes) is determined to occur at 502 and is referred to herein as β _opt. It will be appreciated that the minimum uniform pitch angle includes a prediction of when blade stall occurs and may therefore include an error margin, indicating a blade pitch angle near stall, or in other words, when stall plus a margin pitch angle is likely to occur.

The controller is configured to calculate a maximum IPC pitch angle IPC _max based on a difference between the uniform pitch reference angle β _coll and the minimum uniform pitch angle β _opt, wherein:

IPC_max＝(β_coll-β_opt)。

it should be appreciated that in other examples different functions may be used, so IPC _max may be more generally represented as a function of (β _coll-β_opt). For example, IPC _max＝f(β_coll-β_opt), such as IPC _max＝(β_coll-β_opt) k, where k is an appropriate fraction of the difference between scaled β _coll and β _opt; or IPC _max＝(β_coll-β_opt) ±j, where j is the tuning parameter.

Block 520 includes a difference block that receives β _coll at a non-inverting input and β _opt at an inverting input, where its output includes β _coll-β_opt.

The maximum determination block 521 is configured to output the maximum of its two inputs. Block 521 receives IPC _max at a first input from block 520 and a predetermined zero value shown at block 522 at a second input thereof. Block 521 thus determines the greater of zero and IPC _max and provides it at output 523. Thus, the combination of blocks 520, 521 and 523 is actually a determination of whether the unified pitch reference angle β _coll is greater than the minimum unified pitch angle β _opt and the magnitude of the pitch change is controlled as part of the cyclic IPC control action only if the unified pitch reference angle is greater than the minimum unified pitch angle. In providing this control, the controller at block 521 may output IPC _max to provide a cyclic IPC in accordance with IPC _max and the first and second pitch angle control signals. Otherwise, if the uniform pitch reference angle β _coll is less than the minimum uniform pitch angle β _opt, the controller outputs zero at block 521, disabling the provision of one or more control signals at outputs 507, 508 or at outputs 510-512 to provide cyclic IPC.

In other words, a uniform pitch reference angle that is less than the minimum uniform pitch angle may indicate that the blade is at or near stall (assuming that the minimum uniform pitch angle may include an error margin). Thus, the controller is configured to provide the one or more control signals for enabling cyclic independent pitch control of the blades of the wind turbine only when the uniform pitch reference angle indicates a pitch of the blades 108 that is not stalled. Further, the difference between the uniform pitch reference angle β _coll and the minimum uniform pitch angle β _opt may be understood as the angle from which a blade may pitch from its current pitch while avoiding stall. Therefore, it is referred to as the maximum IPC pitch angle, because it indicates a maximum pitch angle deviation from the uniform pitch reference angle to avoid stall of blade 108.

The first minimum determination block 524 is configured to output the minimum of its two inputs. The first minimum determination block 524 is configured to receive the first pitch angle control signal 505 at a first input and the calculated IPC _max from the output 523 at a second input. The output of the first minimum determination block 524 is the smaller of the first pitch angle control signal 505 and the maximum IPC pitch angle. Thus, this block 524 effectively ensures that the first pitch angle control signal 505 does not indicate a cyclic IPC having a magnitude exceeding the maximum IPC pitch angle (i.e. the magnitude of the blade pitch).

Similarly, the second minimum determination block 525 is configured to output the minimum of its two inputs. The second minimum determination block 525 is configured to receive the second pitch angle control signal 506 at a first input and the calculated IPC _max from the output 523 at a second input. The output of the second minimum determination block 525 is the smaller of the second pitch angle control signal 506 and the maximum IPC pitch angle. Thus, this block 525 effectively ensures that the second pitch angle control signal 506 does not indicate a cyclic IPC having a magnitude exceeding the maximum IPC pitch angle (i.e. the magnitude of the blade pitch).

Thus, in summary, the controller 101 is configured to:

comparing each of the first and second pitch angle control signals to a maximum IPC pitch angle, the maximum IPC pitch angle representing a maximum angle (which may include an error margin) at which the blade can be pitched prior to stall;

wherein if the first pitch angle control signal 505 is greater than the maximum IPC pitch angle IPC _max, then the value at output 526, which continues to form the first pitch angle control output signal, is the maximum IPC pitch angle; and if the first pitch angle control signal is less than the maximum IPC pitch angle, continuing to form the first pitch angle control output signal whose value at output 526 is the first pitch angle control signal; and

Wherein if the second pitch angle control signal is greater than the maximum IPC pitch angle, continuing to form the value at output 527 of the second pitch angle control output signal is based on the maximum IPC pitch angle; and if the second pitch angle control signal is less than the maximum IPC pitch angle, continuing to form the value at output 527 of the second pitch angle control output signal is based on the second pitch angle control signal. This feature may form an aspect of the invention based on the maximum IPC pitch angle received by the controller or the maximum IPC pitch angle calculated from the uniform pitch angle reference and the minimum pitch angle as described above.

Referring to fig. 1 and 2, the present disclosure shows a wind turbine 100 comprising a controller 101 as described herein, wherein the controller is configured to provide a cyclic IPC according to the control actions described herein.

In one or more examples, referring to fig. 3, we provide a controller 101 for a wind turbine 100, in combination with one or more acceleration sensors, configured to detect rapid changes in wind direction based on acceleration information from the one or more acceleration sensors.

Fig. 6 shows a second exemplary embodiment in the form of a functional block diagram similar to fig. 5. The same reference numerals have been used for similar components/functions. As described above, the present control action is configured to provide two main actions. First, the phase shift applied when determining the control signal is controlled to cause a wind direction based cycle IPC. Next, the maximum IPC pitch angle is determined to control the magnitude of the pitch change provided as part of the cyclic IPC. In the controller described in the following embodiments, control of the phase shift is applied to different points.

Thus, block 515, similar to the previous embodiment, is configured to determine whether wind is incident on a first side of the wind turbine or a second side of the wind turbine opposite the first side, thereby determining whether a predetermined phase shift is to be applied. However, rather than applying a predetermined phase shift by blocks 516 and 517 to the D component at output 526 and the Q component at output 527, the phase shift is applied to the phase shift input of the coleman transform at input 514. Thus, referring to fig. 6, the kalman transformation block 518 provided by the controller is configured to transform the D and Q components received at 507 and 508 into one or more control signals for implementing cyclic independent pitching control of the blades of the wind turbine based on the phase offset input received at input 550 and the current azimuth angle of the wind rotor at input 528.

Accordingly, the controller is configured to receive a predetermined reference phase offset at input 514. Through summing block 551, the controller is configured to add or more generally selectively apply the predetermined phase shift determined at block 515 to the phase shift input of the coleman transform as shown at 550. Thus, in one or more examples, the phase of the cyclic IPC applied to the blade is similarly shifted to provide an improved cyclic IPC. Thus, in both embodiments, it has been found that selective variation of the phase of the cyclic IPC may reduce the main bearing stress. In this example, block 515 may selectively apply the predetermined phase shift directly to summing block 551 and not to block 529.

In another embodiment, block 515 is configured to provide two different outputs of predetermined phase shifts; namely the above-mentioned predetermined phase shift (which may also be referred to herein as a first predetermined phase shift) and a second predetermined phase shift. Similar to the alternative embodiment of fig. 5, a similar approach may be provided for the embodiment of fig. 6, wherein a first predetermined phase shift and a second predetermined phase shift are applied/added at a summing block 551. Thus, in this example, block 515 is configured to output a positive (+1) or negative (-1) sign based on one side of the wind turbine upon which wind is incident. The symbol then controls the phase shifted symbol added by summing block 551 by block 529. Thus, block 529 may be configured to provide a 90 degree phase shift that becomes a +90 degree phase shift (a first predetermined phase shift) when block 515 determines that the wind direction is from the first side, and a-90 degree phase shift (a second predetermined phase shift) when block 515 determines that the wind direction is from the second side. It should be appreciated that the controller may apply other first and second predetermined phase shift values. Further, the first predetermined phase shift and the second predetermined phase shift may have different magnitudes.

In terms of the magnitude of the pitch change, the first and second minimum determination blocks 524, 525 provide input to the kalman transform block 518, and there are no phase offset application blocks 516 and 517. Otherwise, the controller provides the same functions as the embodiment described with reference to fig. 5.

FIG. 7 illustrates an example method of providing cyclic independent pitch control for a plurality of blades of a wind turbine. The method comprises the following steps:

receiving 701, 702 at least a first pitch angle control signal and a second pitch angle control signal for controlling the pitch of the blades during cyclic independent pitch control, wherein the first pitch angle control signal and the second pitch angle control signal define a change in blade pitch of the plurality of blades during rotation of the rotor;

Receiving 703 wind direction information indicating a wind direction incident on the wind turbine relative to a direction in which the wind turbine is facing;

Determining 704 a first pitch angle control output signal based on the first pitch angle control signal and a second pitch angle control output signal based on a second pitch angle control signal; and

If the wind direction information indicates a wind direction incident on a first side of the wind turbine, controlling the output signals based on the first and second pitch angles and providing 705 one or more control signals for implementing cyclic independent pitch control of the blades of the wind turbine with a predetermined phase shift;

If the wind direction information indicates a wind direction incident on a second side of the wind turbine, opposite the first side, one or more control signals for implementing cyclic independent pitch control of the blades of the wind turbine are provided 705 based on the first pitch angle control output signal and the second pitch angle control output signal, not with the predetermined phase shift.

It will be appreciated that the controller 101 of fig. 3 may be configured to provide the control actions of the cyclic IPC described in this section, and thus may only require input of a uniform pitch reference angle, a minimum blade pitch reference angle, at least first and second blade pitch control signals, and wind direction information.

Control action of negative thrust control

Control of the wind turbine under negative thrust is extremely important to reduce wear and undesirable loads on the main bearings of wind turbine 100. When the wind turbine is directly facing the wind such that the flow direction of the wind farm is incident perpendicular to the plane of rotation of wind wheel 103, the wind turbine is designated as thrust loading of F _t. Referring to example FIG. 8, a wind turbine designated 100A has a thrust 801 acting in a positive direction. Although shown exaggerated for clarity, wind turbine 100A is loaded and will bend from its vertical position in the direction of thrust, as shown by line 802. It will be appreciated that even when the wind turbine is not facing the wind directly, but the wind arrives from the front of the rotor, the component of force from the incident wind will produce a positive thrust.

The thrust force F _t, which will be familiar to those skilled in the art, is represented by the following equation:

Where A comprises the swept area of rotor 103, ρ comprises the air density, v comprises the wind speed incident on wind turbine 101, and C _t (Ω, β, v) comprises the thrust coefficient.

The thrust coefficient is a function of Ω, including the rotational speed of rotor 103, β, including the pitch angles of blades 108A-C, and wind speed v.

In some cases caused by one or more changes in wind direction, wind speed, and blade pitch angle, negative thrust acting in direction 803 may be generated. Thus, the thrust force F _t is negative. When the thrust is negative, the wind turbine is pulled forward (or pushed forward by the wind direction behind the rotor), as shown at 100B, and it has been found that this may result in high loads on the main bearings.

In the event of a large change in wind direction (e.g., a 90 degree change), wind turbine 100A is no longer subject to thrust in direction 801. Thus, tension in the tower and other components of the wind turbine may cause the wind turbine to spring forward as the tower rebounds, which may result in undesirable vibratory and oscillatory bending movements of the blades and tower. Furthermore, because the wind direction may now be at 90 degrees to the direction in which the rotor is facing, the wind flow may not act to dampen oscillatory bending movements of the blades. Alternatively or additionally, the wind field after the change of direction may act on the rotor to provide negative thrust.

Thus, in one or more examples, it is important to provide a control action that mitigates the generation of negative thrust. Furthermore, providing the control action may be particularly important if negative thrust is detected or determined to be likely to occur, such as in response to the occurrence of rapid changes in wind direction above a threshold level.

Fig. 9 shows an example functional block diagram of the controller 101 according to an example embodiment. It should be appreciated that the example functional block diagram illustrates functionality provided by the controller 101 for mitigating negative thrust, and that the controller may be configured to provide other control actions, which may include control actions provided simultaneously. The functionality shown here may be provided by a programmable logic controller. Or the filters and/or amplifiers may comprise discrete signal processing components. In another embodiment, the controller may provide a software-based implementation of the functionality shown. Combinations of the above embodiments are also within the scope of the present disclosure.

In general, the negative thrust mitigating control actions of the present embodiments are configured to define a maximum blade pitch angle that is not exceeded. Thus, the controller 101 may be configured to provide one or more other control actions that control the pitch of the blade, but if the blade pitch determined by these one or more other control actions is greater than (or more generally exceeds) the determined maximum blade pitch angle defined by the current control action, the controller may be configured to: (a) Limiting the blade pitch to the determined maximum blade pitch angle, and/or (b) ignoring the blade pitch determined by one or more other control actions so as not to issue a control signal that would cause the blade to adopt such a pitch angle.

An example control action will now be described with reference to fig. 8, fig. 8 showing the functions of the present embodiment provided by the controller 101. First, the controller 101 is configured to receive a plurality of inputs.

The controller 101 may be configured to receive rotational speed information from a rotational speed sensor 309 at an input 303. It will be appreciated that two different functional blocks receive rotational speed information and therefore are both labeled as inputs 303.

The controller 101 may be configured to receive wind speed information from a wind speed sensor 307 at an input 301. It will be appreciated that two different functional blocks receive wind speed information and therefore are both labeled as inputs 301.

The controller 101 may be configured to receive air density information at input 901, which may be predetermined air density information. Thus, input 901 may be an example of information received at input 304 from one or more other sources. The air density information may indicate a current density of air in a wind farm incident on the wind turbine. The air density information may be calculated by a different process performed by the controller 101 or another controller. In one or more examples, the air density information may be determined based on information from an atmospheric pressure sensor (not shown) and/or a temperature sensor (not shown). In one or more examples, the controller may be configured to invoke a predetermined air density from a data store (not shown), which may be a fixed value or a dynamically updated value. The air density may be estimated and provided to the controller. The air density may be estimated based on one or more of temperature and barometric pressure.

Controller 101 may be configured to receive blade pitch angle information at input 902 that includes a current pitch angle of blades 108A-C. Thus, as well, input 901 may be an example of information received at input 304 from one or more other sources. In one or more examples, the pitch of the blades 108A, 108B, 108C may be controlled, i.e., rotation about the longitudinal axis of each blade. Thus, each blade 108A, 108B, 108C is rotatably mounted to the hub 107 and coupled with an actuator to control the pitch of the blade. Accordingly, controller 101 may be configured to provide one or more control signals to control the actuators to change the pitch of one or more blades 108A-C of rotor 103. One or more blade pitch sensors may be provided to measure the current pitch of blades 108 to provide blade pitch angle information to the controller. In other examples, it should be appreciated that the controller 101 may actively control the pitch of the blade by issuing one or more control signals to the blade pitch actuators as part of different control actions, and the blade pitch information may be based on these control signals.

In one or more examples, controller 101 may optionally receive an indication of the occurrence of an event at input 903 that the rapid change in wind direction is above a threshold level. Thus, in one or more examples, the control actions for determining the maximum blade pitch angle may be performed in response to the occurrence of a rapid change in wind direction above a threshold level event, but in other examples, the control actions for determining the maximum blade pitch angle may be performed at other times. A rapid change in wind direction may be defined as a 30 degree or greater change in wind direction that occurs in a time period of less than 30 seconds. Other threshold levels and ways of determining the occurrence of such fast changing events may be used.

The controller 101 may be configured to determine a thrust limit, wherein the thrust limit defines a minimum thrust on the wind turbine 100 that the controller attempts to maintain by controlling the pitch of the blades. In the following example, the controller attempts to maintain a minimum positive thrust. As described above, the positive thrust is in the direction 801 towards the front of the rotor. The thrust limit is determined by function block 904. However, in other examples, less negative thrust may be allowed.

In one or more other examples, the thrust limit may include a predetermined value, and thus the thrust limit may not need to be determined by block 904. Thus, in such other examples, block 904 may not be present, but rather may provide a predetermined thrust limit at input 905.

The predetermined thrust limit may include zero. Thus, the controller may be configured to prevent negative thrust by providing a control action that includes controlling the pitch of the blades to avoid the thrust from falling below zero (or attempting to do so) so as to subject the wind turbine 100 to negative thrust. In other examples, the predetermined thrust limit may be greater than zero. A thrust limit greater than zero may be advantageous because providing a control action to ensure that there is a (e.g., small) positive thrust may act to dampen or dampen any undesired vibratory or oscillatory bending of blades 108 or tower 102. In one or more examples where the thrust limit is defined in newtons, the beneficial thrust limit may be between 200kN and 600 kN. Or the thrust limit may be expressed in terms of rated thrust: in these examples, the beneficial thrust limit may be between 25% and 100%. The rated thrust may include a predetermined thrust that may be determined as an upper limit force to which the wind turbine should be subjected in normal use.

In one or more other examples, the predetermined minimum thrust may include a negative thrust within a predetermined negative thrust threshold of zero thrust, which may be considered acceptable. Thus, the controller may be configured to allow for a small negative thrust.

It will be appreciated that wind turbines are subject to changing environmental conditions and that the controller 101 or other controller may provide for a change in blade pitch to achieve other objectives, so the control actions described herein to prevent negative thrust may be understood as control actions that attempt to prevent negative thrust, but may not always be achievable in practice in view of the changing environmental conditions. However, it has been found that the control actions described in this section may reduce the chance that the wind turbine is subjected to negative thrust, which is advantageous.

In this example, the thrust limit is determined by the controller 101. Block 906 shows that the controller 101 is configured to determine the current thrust based on the following equation:

Wherein the wind speed information received at input 301 provides a term v, the blade pitch angle information received at input 902 provides a term β, the air density information received at input 901 provides a term ρ, the rotational speed information received at input 303 provides a term Ω, and the predetermined value indicative of the swept area of the rotor 103 provides a term a.

In one or more examples, block 906, and thus controller 101, is configured to provide an output of the current thrust for determining a thrust limit at output 907, wherein the thrust limit defines a minimum positive thrust on the wind turbine that the controller attempts to maintain by controlling the pitch of the blades. Accordingly, the controller may be configured to determine the thrust limit based on the current thrust experienced by the wind turbine or the thrust experienced during the last time period. This may be advantageous because the thrust limits are dynamic and based on current conditions, may therefore be of a magnitude that suppresses any resultant vibrations caused by thrust changes or potentially negative thrust changes. The most recent time period may include up to 100 seconds prior to the current time, or between 1 and 100 seconds prior to the current time, or between 10 and 20 seconds prior to the current time. Thus, in one or more examples, the current thrust at which the wind direction changes rapidly may be used. In other examples, a current thrust of 5, 10, 15, or 20 seconds before the wind direction changes rapidly may be used. The controller may be configured to buffer the most recent calculation of the current thrust in a buffer so that when a rapid change in wind direction is detected, the controller may react with the appropriate current thrust value.

In this example, the thrust limit provided at input 905 includes an appropriate fraction of the current thrust determined at 907. An amplifier or attenuator 908 is shown that determines an appropriate fraction of the current (positive) thrust. Thus, the amplifier 908 may have a gain K (representing an appropriate fraction as described above), where K is between-0.1 and 0.75, preferably between 0.1 and 0.3. Thus, whether through the use of amplifier 908 (which may also be referred to as an attenuator) or through software-defined calculations, the controller may be configured to determine a thrust limit based on an appropriate fraction of the current thrust experienced by the wind turbine. It will be further appreciated that when K is between 0 and-0.1, a small negative thrust is allowed, which is acceptable in one or more examples.

Block 904 also includes a latch 910 that receives an indication of the occurrence of an event that a rapid change in wind direction is above a threshold level. Latch 910 may be configured to latch (i.e., hold) the current thrust value at output 907 based on the occurrence of an event that the rapid change in wind direction is above a threshold level. Thus, in one or more examples, controller 101 may be configured to determine the thrust limit based on an appropriate fraction of thrust experienced by wind turbine 100 when a rapid change in wind direction is detected above a threshold level or within a predetermined time thereof (e.g., a predetermined time prior to a rapid change in wind direction above a threshold level event).

The thrust limit, whether predetermined or calculated in block 904, is provided to a thrust coefficient determination block 911. Block 911 is configured to receive air density at input 901 and wind speed information at input 912. In one or more examples, the wind speed information provided to block 911 includes average wind speed information over a predetermined recent period of time. Accordingly, one example embodiment may include providing a low pass filter 913 configured to receive wind speed information from input 301. The low pass filter 913 is configured to filter the wind speed information to determine filtered wind speed information indicative of said average wind speed information over a predetermined recent time period. The time constant of the low pass filter may be set to 5 seconds or between 1 and 10 seconds or between 3 and 7 seconds.

The thrust coefficient determination block 911 calculates a minimum thrust coefficient C _t-min (Ω, β, v) that will provide the thrust limiting force determined and received at the input 905 using the following equation:

Where V comprises the current or average wind speed based on wind speed information received at input 301, ρ comprises air density information received at input 901, a comprises a predetermined value indicative of the swept area of rotor 103, and F _thrust-limit comprises the thrust limit received at 905. More generally, the minimum thrust coefficient C _t-min is determined as a function of the thrust limit divided by the square of the current or average wind speed. Thus:

The minimum thrust coefficient C _t-min (Ω, β, v) calculated by block 911 is provided to a maximum pitch angle determination block 914. Block 914 is configured to receive wind speed information from input 301 or wind speed based on the wind speed information, such as average wind speed information from low pass filter 913. Block 914 is also configured to receive rotational speed information from the input 303. In one or more examples, the rotational speed information provided to block 914 includes average rotational speed information over a predetermined recent period of time. Accordingly, one example embodiment may include providing a low pass filter 915 configured to receive rotational speed information from the input 301. The low pass filter 915 is configured to filter the rotation speed information to determine filtered rotation speed information indicative of the average rotation speed information over a predetermined recent period of time. The time constant of the low-pass filter 915 may be set to 5 seconds or between 1 and 10 seconds or between 3 and 7 seconds. In some examples, the time constant of the low pass filter 915 may be set to be up to 100 seconds.

The maximum pitch angle determination block 914 is configured to determine a maximum pitch angle β _max based on the minimum thrust coefficient C _t-min, wind speed information (which may include the current wind speed or moving average), and rotational speed information (which may include the current rotational speed or moving average of the rotor).

It should be appreciated that β _max can be determined by the following equation:

In one or more examples, the controller is configured to determine β _max with reference to a lookup table that provides β _max for a plurality of rotational speeds, wind speeds, and minimum thrust coefficients C _t-min. The look-up table may be predetermined and stored in a memory accessible to the controller. In other examples, the maximum pitch angle β _max is determined by an optimization problem that the controller is configured to solve by minimizing or maximizing an objective function of β _max, as is familiar to those skilled in the art.

The output of controller 101, particularly the output of the current negative thrust alleviation control action, is the maximum pitch angle at output 916.

Thus, in general, the controller 101 may be configured to:

Receiving wind speed information indicative of a wind speed from a wind speed sensor;

Receiving rotational speed information indicating rotational speed of the wind wheel from a wind wheel rotational speed sensor;

Determining a minimum thrust coefficient C _t-min comprising a thrust coefficient providing a predetermined minimum positive thrust on the wind turbine, wherein

Wherein V comprises wind speed based on the received wind speed information, ρ comprises an air density based on the air density information, A comprises a predetermined value indicative of a swept area of the rotor 103 of the wind turbine, and F _thrust-limit comprises a predetermined minimum positive thrust; and

A maximum pitch angle β _max is determined based on the minimum thrust coefficient C _t-min, the wind speed information, and the rotational speed information, wherein the controller is configured to provide control signals to control a blade pitch of one or more blades of the wind turbine to not exceed the maximum pitch angle.

Example fig. 10 shows a flow chart illustrating a method of controlling a wind turbine 100. The method comprises the following steps:

Receiving 1001 wind speed information from a wind speed sensor;

Receiving 1002 rotational speed information from a rotor rotational speed sensor configured to measure rotational speed of the rotor;

Determining 1003 a minimum thrust coefficient C _t-min comprising a thrust coefficient providing a predetermined minimum positive thrust on the wind turbine, the minimum thrust coefficient comprising a function of a wind speed based on the received wind speed information, an air density based on the air density information, a predetermined value indicative of a swept area of a wind rotor of the wind turbine and the predetermined minimum positive thrust;

determining 1004 a maximum pitch angle β _max based on the minimum thrust coefficient C _t-min, the wind speed information and the rotational speed information; and

One or more control signals are provided 1005 to control the blade pitch of two or more blades of the wind turbine without exceeding the maximum pitch angle.

Example fig. 11 shows a plot of blade pitch angle on axis 1101 versus time on axis 1102 to provide an example of the action of controller 101. It should be appreciated that the controller or other process may control the pitch of the blades, which will be referred to as controlled blade pitch. The controller in this example ensures that the controlled blade pitch does not exceed the determined maximum pitch angle.

The dashed line shows the determination of the maximum pitch angle. Thus, at time 1103, the occurrence of a rapid change in wind direction above a threshold level event may be determined by any suitable method. It will be appreciated that for the purpose of this negative thrust mitigation control action, it is not important how this is detected, but it is advantageous to provide the control action during or in response to an event. Thus, a maximum pitch angle is established. At time 1104, i.e. between time 1103 and time 1105, the controller is configured to ensure that the controlled blade pitch does not exceed the maximum pitch angle defined by the dashed line. The controller is configured to limit the controlled blade pitch to the determined maximum blade pitch angle if the controlled blade pitch is greater than the determined maximum pitch angle. Thus, the controlled pitch angle may be set to any pitch angle in region 1106, but if the controller determines that the controlled pitch angle is in region 1107, the controller may limit the pitch angle to follow the dashed line at time 1104.

In this example, the controller is configured to provide a control action to mitigate negative thrust for a predetermined duration after detecting a rapid wind direction change event. The predetermined duration is shown here as the difference between time 1105 and time 1104.

Control action for closing wind turbine generator system

In some cases, it may be desirable to shut down wind turbine 100. As shown in step 406 of fig. 4, the shutdown may be performed in response to the occurrence of a rapid change in wind direction above a threshold. Shutdown involves decelerating the rotor to a minimum rotor speed, which typically involves stopping or approaching a stop of the rotor. The shutdown of the wind turbines may be defined by control actions performed by the controller 101. However, it has been found that the default shutdown control actions may not be appropriate in all circumstances, or in other words, may be limited in some circumstances.

After the wind direction has changed rapidly, wind turbine 100 will operate with high yaw error. In general, higher yaw errors occur when the difference between the wind turbine orientation (i.e., nacelle orientation) and the current wind direction is large (e.g., greater than 30 degrees or 40 degrees). As known to those skilled in the art, rapid changes in wind direction cause high yaw errors, the components vibrate or oscillate in various modes, causing high levels of vibration in the wind turbines. In particular, vibrations of 1P and 3P frequencies occurring in the stationary gantry, as well as vibrations occurring in the rotating gantry at 2P frequencies (where P represents the rotational speed of the wind turbine), are excited. Furthermore, when at high yaw errors, the aerodynamic damping of these vibrations is low, as the wind flow may not act against the direction of the vibrations. Thus, operating a wind turbine with a rotational frequency of the rotor that coincides with the structural resonant frequency (including vibration modes) of the tower and/or blades tends to result in high levels of vibration, which may be much higher than during normal operation. Thus, in summary, when aerodynamic damping is low, rapid changes in wind direction may cause high levels of excitation in the tower and/or blades.

It may also be desirable to take into account the speed limit at which the control action is implemented. For example, there is a limit to how much torque (torque) the generator can apply before a manufacturer-defined threshold is exceeded. Furthermore, the speed at which the blade pitch actuator changes the pitch of the blade is limited. In addition, there may be other limitations on the rate of change of blade pitch, as other control actions may impose limitations to mitigate other undesirable effects. For example, the current shutdown control action may be provided in combination with a control action for negative thrust control, so that if it is determined that a change in blade pitch would cause an undesirable negative thrust on the wind turbine, the change may be limited.

FIG. 13 shows an exemplary plot of rotor frequency versus rotor speed. The first, second and third dashed lines 1301, 1302, 1303 show 1P, 2P and 3P relations, respectively, where P represents the rotor speed. In addition, horizontal lines of different frequencies are shown, which frequencies correspond to the resonant frequencies or modes of vibration of the tower and blades. In particular, line 1304 represents the edgewise (backward whirl) vibration mode. Line 1305 represents the first swing direction (flapwise) uniform vibration mode. Line 1306 represents a first front-to-back or lateral tower vibration mode. Line 1307 represents the flapwise cyclic vibration mode.

Fig. 13 also shows the location where these vibration modes coincide with lines 1301-1303 of 1P, 2P and 3P. Circle 1308 shows the location where the 3P line coincides with line 1305 indicating the rotor speed which will cause the first swing direction to unify the undesired vibrations. Circle 1309 shows the location where the 2P line coincides with line 1306 indicating the rotor speed that would cause undesirable tower vibration. Circle 1310 shows the location where the 2P line coincides with line 1307 indicating the rotor speed that would cause an undesirable first swing direction cyclic vibration. Circle 1311 shows the location where the 3P line coincides with line 1304 indicating rotor speed that would cause undesired shimmy direction backspin.

It has been identified that the range of rotational speeds specified by block 1312 encompasses a large number of these coincidences. It should be appreciated that for clarity, other vibration modes not shown are typically present. Block 1313 shows a lower range of rotor speeds that the shutdown control action may be directed to bring the rotor to.

Example fig. 14 illustrates a functional block diagram of how the controller 101 configures operation. The controller includes a shutdown mode decision block 1400. Block 1400 is configured to receive a shutdown request at a first input 1401, the shutdown request including a request to reduce a rotor speed to at least a predetermined minimum rotor speed (e.g., speed 1320 in fig. 13). In one or more examples, the predetermined minimum rotor speed is zero or substantially zero. In other examples, a small remaining rotor speed may be acceptable. In this example, the predetermined minimum rotor speed includes less than 0.3 radians/second. However, the predetermined minimum rotor speed may be expressed in different ways. Thus, the predetermined minimum wind turbine speed may comprise less than 25%, 20%, 15% or 10% of the rated speed of the wind turbine, wherein the rated speed comprises the predetermined value. The rated rotational speed of a wind turbine is a common parameter associated with wind turbines, including the rotational speed at which the wind turbine provides its full rated power output.

Block 1400 is also configured to receive rapid wind direction change information at a second input 1402. When a rapid change in wind direction above a threshold level occurs, rapid wind direction change information informs the controller and block 1400. In one or more examples, the rapid change in wind direction above a threshold level may include a change in wind direction of greater than 30 degrees occurring in no more than 30 seconds. However, rapid changes in the wind direction determined to be the one that the controller should act on may vary between wind turbines. However, it should be appreciated that when there is a high yaw error and therefore low aerodynamic damping, the controller is informed of rapid wind direction change information and that at the indicated rotor speeds, the vibration modes of FIG. 13 may appear undamped.

Block 1400 may also be configured to receive the current rotor speed at a third input 1403. The one or more control actions provided by the controller may be based on or require feedback of the current rotor speed or its nearest average.

As described above, the pitch of blades 108 is controllable, the torque applied by generator 105 to rotor 103 is controllable, and the controller may be configured to control these parameters to achieve a shutdown of the wind turbine.

The controller is configured to provide a first shutdown mode, which may be considered a default shutdown mode, as represented by block 1404. In providing the first shutdown mode, the controller is configured to provide one or more first shutdown control signals to provide one or both of (a) a change in blade pitch of one or more of the plurality of blades to slow down the wind turbine and (b) a change in torque applied to the wind turbine by the generator to slow down the wind turbine. The first shutdown mode may include a steady and sustained decrease in rotor speed subject to any external constraints.

The controller is configured to provide a second shutdown mode represented by block 1405. The second shutdown mode is different from the first shutdown mode. The second shutdown mode may differ from the first shutdown mode in one or more of providing a speed of shutdown, a rate at which the rotor is decelerated, or a strategy to vary generator torque and blade pitch to decelerate the rotor and achieve shutdown. In providing the second shutdown mode, the controller 101 is configured to provide one or more second shutdown control signals to provide one or both of (a) a change in blade pitch of one or more of the plurality of blades to slow down the wind turbine and (b) a change in torque applied to the wind turbine by the generator to slow down the wind turbine. Typically, both generator torque and blade pitch are varied to achieve shutdown in both modes.

A second shutdown mode may be provided to shut down the wind turbine faster, which is desirable when the wind turbine is subject to rapid changes in wind direction.

Thus, the one or more second shutdown control signals of the second shutdown mode are configured to decelerate the wind turbine at a faster rate than the one or more first shutdown control signals, at least over a predetermined range of rotational speeds. The predetermined range of rotational speeds is defined to include at least one rotational speed corresponding to a resonant frequency of one or more of the wind rotor, tower, or blades, such as shown in fig. 13. Thus, in one or more examples, the predetermined range of rotational speeds may correspond to the rotational speed of block 1312. The controller may be configured to receive rotational speed information indicative of rotational speed of the rotor, such that control may be provided to slow the rotor down within a predetermined range of rotational speeds. In other examples, the rotational speed may be inferred by learning an expected effect of one or more second shutdown control signals or other measurements.

Thus, the shutdown mode decision block 1400 is configured to receive a shutdown request from the first input 1401 and rapid wind direction change information from the second input 1402, and determine whether to provide the first shutdown mode or the second shutdown mode. In case of rapid changes of wind direction, it has been found to be advantageous to switch off the wind turbine 100 faster, in particular when the rotor speed is within a predetermined range of speeds. Thus, the shutdown mode decision block 1400 is configured to provide a second shutdown mode instead of the first shutdown mode based on receiving rapid wind direction change information indicating that a rapid change in wind direction above a threshold level occurs.

It will be appreciated that the second shutdown mode may be activated at times other than when the wind direction rapidly changes above a threshold level, for example in an emergency. However, for purposes of this embodiment, selecting the second shutdown mode instead of the "default" first shutdown mode is based on rapid changes in wind direction that are or have recently been above a threshold level.

Accordingly, the controller 100 as shown in block 1400 is configured to select a default first shutdown mode when a shutdown request is received and no indication of a rapid change in wind direction above a threshold level occurs in the rapid wind direction change information.

As described above, example FIG. 13 illustrates different vibration modes that may be excited in a wind turbine tower or blade. However, as known to those skilled in the art, many other modes of vibration or oscillation exist.

Thus, the predetermined range of rotational speeds may include rotational speeds corresponding to one or more of the following resonant frequencies:

(a) Unified excitation frequency of the first swing direction;

(b) An excitation frequency associated with the back-and-forth oscillations of the tower;

(c) An excitation frequency associated with lateral oscillations of the tower;

(d) Blade flapping frequency of one or more of the plurality of blades;

(e) A uniform flapping frequency for all of the plurality of blades;

(f) A uniform shimmy frequency for all of the plurality of blades;

(g) Forward and backward rotation of the flapping frequency;

(h) A shimmy frequency of forward and backward rotation;

(i) The tower torsion (torsional) excitation frequency; and

(J) Blade torsional excitation frequency.

Further, the predetermined range of rotational speeds may include a continuous speed range covering one or more, two or more, or three or more of the resonant frequencies listed above. In other embodiments, the predetermined range of rotational speeds may include a discontinuous range of rotational speeds focused on two or more resonant frequencies.

It has been found that after a rapid change in wind direction, the frequency corresponding to the flapping oscillation mode may be more problematic. In one or more examples, the flapping frequencies are prone to destructive oscillations when not damped by wind flow, and thus by defining a predetermined range of rotational speeds based on these frequencies, the controller can mitigate this effect by slowing down the rotor faster within the predetermined range of rotational speeds and by these frequencies when slowing down the rotor. Thus, in one or more examples, the predetermined range of rotational speeds includes rotational speeds corresponding to a combination of one, two, three, or more of the flap frequencies. Thus, the frequencies listed at (a), (d), (e) and (g) may be included within a predetermined range of the rotational speed.

Further, in one or more examples, the predetermined range of rotational speeds includes rotational speeds at which at least one of 1P and 2P and 3P (where P represents rotational speed of the rotor) corresponds to one or more of:

(a) Unified excitation frequency of the first swing direction;

(c) Blade flapping frequency of one or more of the plurality of blades;

(d) A uniform flapping frequency for all of the plurality of blades; and

(E) Forward and backward rotation of the flapping frequency.

It will thus be appreciated that certain vibration modes are excited at multiples of the rotor speed, and thus it may be advantageous to identify speeds of 2P, 3P and in some examples 4P, 6P and 9P corresponding to frequencies of problematic vibration modes when defining predetermined ranges.

In one or more examples, the predetermined range of rotational speeds is focused on rotational speeds corresponding to vibration modes of the tower and/or blades and multiples thereof. Thus, the predetermined range of rotational speeds may extend between a lower (lower limit) rotational speed 1321 and a higher (upper limit) rotational speed 1322. The higher rotational speed 1322 is defined by the vibration pattern of one or more of the rotor or tower or blades plus a rotational speed corresponding to a first threshold amount. Thus, it can be seen in fig. 13 that the value of the higher threshold amount is slightly greater than the value of circle 1308 corresponding to the 3P vibration mode. Further, the lower rotational speed 1321 may be defined by a rotational speed corresponding to a resonant frequency or vibration mode of one or more of the wind rotor, tower, or blades minus a second threshold amount. Thus, the difference between circle 1310 and lower rotational speed 1321 may correspond to a second threshold amount. Thus, in this example, the second threshold amount is greater than the first threshold amount. However, in other examples, different first and second threshold amounts may be used.

Now we further consider the difference between the first shutdown mode provided by the controller as shown in block 1404 and the second shutdown mode provided by the controller as shown in block 1405.

In this and other examples, the one or more second shutdown control signals provide for application of a greater generator torque than the one or more first shutdown control signals to slow the wind rotor at least at a predetermined range of rotational speeds corresponding to the rotational speeds. Thus, a faster deceleration of the rotor within a predetermined range of rotational speeds may be achieved, at least in part, by selectively applying a greater generator torque.

It should be appreciated that the controller may provide the effect of increased generator torque in any suitable manner. However, in the first example, the application of the greater generator torque is provided by a second shutdown control signal configured to cause an increase in voltage across one or more coils of the generator, which in turn will increase the current through the coils of the generator, thereby achieving the effect of increasing the torque that slows the rotor. In other examples, the second shutdown control signal may be configured to request an increase in power output of the generator, which has the effect of increasing torque on the rotor, slowing the rotor.

In one or more examples, the torque applied at any one time during the second (and first) shutdown modes may vary. Thus, the larger generator torque applied during the second shutdown mode may be a larger average torque over a range of rotational speeds or an average torque over a predetermined time. Thus, the second shutdown mode may provide a greater average torque over a period of time between 10 seconds and 60 seconds, which may correspond to the time it takes for the second shutdown mode to complete or only partially complete. In other examples, the greater generator torque applied during the second shutdown mode may be a greater peak torque.

The operation of wind turbines is typically controlled by various operational constraints. Operational limits are typically set by the manufacturer to prevent or limit the stress or torque on the component to unacceptable levels, thereby allowing the component to function over its intended life. Other operational limits may be imposed because if these limits are exceeded, the temperature, current, voltage or force on one or more components may reach levels that are not desirable for the unit's effective function over its useful life. One of the operating limits may include a generator torque limit. The generator torque limit may be provided by the controller and defines an upper limit on the torque that the generator 104 should apply to the rotor 103. It should be appreciated that the generator may be physically capable of applying greater torque, but such application may be considered to place undue stress or load on the components such that it is undesirable during normal operation. Rapid changes in wind direction above a threshold level may be rare events, but the stresses/pressures they may cause may be significant. Thus, in some examples, it may be determined or probabilistically appreciated that, although stress/pressure may be caused, on average, stress/pressure exceeding operational limits may be less than stress/pressure caused by rapid changes in wind direction above a threshold level.

Thus, in one or more examples, the controller 101 is configured to perform a generator torque limit defining a maximum torque that the one or more first shutdown control signals cause the generator to be applied to the wind rotor during the first shutdown mode. It should be appreciated that the generator torque limit may also be applied to one or more or all of the control processes other than the second shutdown mode.

However, the controller may be configured to provide the one or more second shutdown control signals to cause the generator to apply a torque greater than the generator torque limit during the second shutdown mode, thereby exceeding the generator torque limit. In some examples, exceeding the generator torque limit may only be caused when the rotational speed of the rotor is within a predetermined range of rotational speeds.

It will be appreciated that the deceleration of the rotor may also be achieved by adjusting the blade pitch towards the feathered orientation. In one or more examples, blade pitch may be adjusted in conjunction with changes in generator torque. Or in this example, the controller is configured to provide the one or more second shutdown control signals while providing the second shutdown mode of block 1405 such that they cause the pitch of the plurality of blades to change toward the feathered blade when the generator applies a torque greater than the generator torque limit. In some examples, the controller may define a second generator torque limit that includes a greater generator torque than the generator torque limit, the generator torque limit being acceptable under limited conditions, such as during the second shutdown mode.

Further, in one or more examples, an adjustment of the blade pitch feathering orientation may be provided in response to the generator torque reaching a second generator torque limit. Thus, the controller may not change the blade pitch as part of the second shutdown mode before the second generator torque limit (or generator torque limit) is reached.

While the purpose of the second shutdown mode is to quickly reduce the rotational speed of the rotor, it is not always possible to achieve this at the fastest rate allowed by the various blade actuators and generators. The wind turbines will be subjected to various forces during shutdown and these forces need to be managed by one or more other control processes outside of the second shutdown mode described herein. However, in general, for the purposes of the present control procedure, these one or more other control procedures have the effect of defining a limit of the blade pitch angle or the rate of change of the blade pitch angle at a particular point in time during the execution of the second (and first) shutdown mode.

Thus, the controller 101 may be configured to receive blade pitch limit information defining a temporary limit on the blade pitch at a certain point in time. The blade pitch limit (including rate change) may be explicit information provided to the presently described control actions. In other examples, since the one or more other control processes have been interposed to limit the blade pitch, blade pitch limit information may be inferred based on feedback of the current blade pitch that does not match the expected blade pitch. As described herein, one example of the blade pitch limit information may be determined by a controller to mitigate negative (e.g., large) thrust forces exerted on a wind turbine.

Thus, the one or more second shutdown control signals may be configured to change the pitch of the plurality of blades towards the feathered blade orientation without exceeding the temporary limit of blade pitch.

When the rotor speed is greater than the low rotor speed threshold, which may include speed 1321 in fig. 13, the speed 1321 defining a predetermined range of lower speeds, the controller may be configured to orient the blades to pitch toward feathering at a first pitch rate at least within a threshold of a maximum pitch rate of the blades. This may include feathering at as fast a rate as possible in accordance with any blade pitch limit information. In other examples, the threshold value of the maximum pitch rate may be within 5% of the maximum pitch rate, i.e., between 95% and 100% of the maximum pitch rate. The maximum pitch rate may be determined as the maximum rate at which the blade pitch actuator is able to rotate the blade in the control of the blade pitch.

However, when the rotor speed is less than the low rotor speed threshold (which may be speed 1321), the controller 101 may cause the blades to pitch toward feathering at a second pitch rate that is less than the first pitch rate. Thus, when the rotational speed of the rotor reaches a low rotor speed threshold, the rate of change of pitch may slow. The second pitch rate may comprise a constant pitch rate subject to any temporary limitations imposed by the blade pitch limit information.

Thus, in one or more examples, the controller may pitch at a pitch rate within a predetermined range of rotational speeds, and then, when a low rotor speed threshold is reached, change the process to pitch toward feathering at a second rate. However, in another example, when the second pitch rate is employed, the controller may be configured to determine when a predetermined pitch angle is reached and in response thereto increase the blade pitch rate to orient the blades toward feathering at a third rate that is greater than the second pitch rate.

To illustrate the comparison between the default first shutdown mode and the second shutdown mode of rapid wind direction change described above, the first shutdown mode may be as follows. The one or more first shutdown control signals may provide the function of reducing the rotational speed of the rotor by controlling pitching of the blades towards feathering. The one or more first shutdown control signals may provide for application of generator torque to slow down the rotor. The one or more first control signals may cause the rotor to decelerate at one or more rates regardless of the predetermined range of rotational speeds. For example, any change in the one or more first control signals is independent of rotor speed being within a predetermined speed range.

In the above example, the controller may be configured to monitor the rotor speed when the second shutdown mode is provided such that an associated control to increase the generator torque may be provided at least when the rotor speed is within a predetermined range of rotor speeds. However, we now disclose a different control scheme. As described above with respect to fig. 13, the basic principle of providing a faster deceleration within a predetermined range of rotor speeds is to avoid excessive vibrations at the resonant frequency. Thus, in this alternative example, the speed of the rotor speed being within the predetermined rotor speed range is determined based on received acceleration information indicative of the acceleration experienced by one or both of the tower and nacelle of the wind turbine. Thus, when the received acceleration information indicates a vibration level above a threshold value, it may be inferred that the rotor speed is within a predetermined range of the rotor speed.

Thus, during the providing of the second shutdown mode, the controller is configured to provide the one or more second shutdown control signals such that the pitch rate oriented toward the feathered blades increases based on acceleration information indicative of vibrations above a first threshold vibration level. The increase in pitch rate may be an increase to within a maximum pitch rate threshold of the blade or an increase to a maximum pitch rate. The maximum pitch rate may be the maximum rate at which blade pitch may be changed.

In one or more examples, the amount of generator torque may be increased based on acceleration information indicative of vibrations above a first threshold vibration level.

Further, in one or more examples, the controller may be configured such that the pitch rate oriented toward the feathered blades is reduced based on acceleration information indicative of vibrations below a second threshold vibration level (which is below a first threshold vibration level). The decrease in pitch rate may be to a predetermined pitch rate or below such a predetermined pitch rate.

In one or more examples, the amount of generator torque may be reduced based on acceleration information indicative of vibrations below a second threshold vibration level.

The first threshold level and the second threshold level may be the same or different.

As part of the shutdown, the controller may electrically disconnect the generator from a power inverter that connects the wind turbine to the grid. By grid we mean the distribution network to which the wind turbines are typically connected, but may also be a local load. Thus, the controller may provide control of one or more relays that provide electrical coupling between the generator and the power converter and/or the grid. The first and second shutdown modes may differ in the manner of disconnection.

Typically, the one or more first shutdown control signals provided during the first shutdown mode are configured to provide a generator disconnection process such that the torque applied by the generator to the wind rotor slowly decreases within a non-zero torque reduction time (or reaches zero torque) to within a zero torque threshold before the generator is disconnected from the grid-connected power converter of the wind turbine. However, considering that the second shutdown mode is intended to provide a faster shutdown, it may not be feasible to slowly reduce the generator to a zero torque state.

Thus, in one or more examples, the second shutdown control signal provided during the second shutdown mode may be configured to disconnect the generator from the grid-tied power converter when the torque applied by the generator is greater than a torque threshold. While this may not minimize stress on the generator as in the first shutdown mode, in the rare case of abrupt changes in wind direction, this may be considered a compromise that is worth taking in order to reduce damage caused by undamped vibrations.

Referring to fig. 1 and 2, we also disclose a wind turbine comprising a controller 101, the controller 101 performing the above-described control actions for shutdown.

Example figure 15 shows a flow chart for controlling a wind turbine during a shutdown. This is a method of slowing the rotor to a stop or near-stop.

The example method includes receiving 1501 a shutdown request including a request to reduce a rotational speed of a rotor to at least a predetermined minimum rotor rotational speed;

receiving rapid wind direction change information 1502, the rapid wind direction change information 1502 indicating that a rapid change in wind direction above a threshold level occurred; and

When a shutdown request is received, a second shutdown mode 1504 is provided instead of the first shutdown mode 1503 based on receiving rapid wind direction change information indicating that a rapid change in wind direction above a threshold level has occurred.

Fig. 16 shows a computer program product 1600 comprising computer program code for implementing the method of fig. 4 and/or the method of fig. 7 and/or the method of fig. 10 and/or the method of claim 15. Computer program product 1600 may include a USB mass storage device or other medium for updating software or firmware of controller 101 of wind turbine 100.

Claims

1. A controller for providing cyclic independent pitch control of a plurality of blades of a wind turbine, the controller being configured to:

2. The controller according to claim 1, wherein

The first pitch angle control signal comprises a D component for controlling a direct-to-quadrature axis shift of a pitch of the blade during cyclic independent pitch control; and

The second pitch angle control signal comprises a Q component for controlling a direct-to-quadrature axis shift of a pitch of the blade during cyclic independent pitch control.

3. The controller of claim 1 or claim 2, wherein the controller is configured to:

4. A controller according to claim 2, wherein the providing the one or more control signals for enabling cyclic independent pitch control comprises applying a golman transformation to the first and second pitch angle control output signals, and wherein the controller is configured to apply the predetermined phase shift to a phase shift input of the golman transformation, wherein the controller is configured to provide the one or more control signals for enabling cyclic independent pitch control of the blades of the wind turbine based on the first and second pitch angle control output signals and the golman transformation of the phase shift input and information indicative of a current azimuth angle of the wind rotor, so as to provide the one or more control signals for enabling cyclic independent pitch control with the predetermined phase shift.

5. A controller according to any preceding claim, wherein the predetermined phase shift comprises a phase shift between 120 degrees and 240 degrees.

6. The controller of any of claims 1 to 4, wherein the predetermined phase shift comprises a 180 degree phase shift.

7. A controller according to any one of claims 1 to 4, wherein the predetermined phase shift comprises a function of wind direction information.

8. A controller according to any preceding claim, wherein the controller is configured to:

9. A controller according to any preceding claim, wherein the controller is configured to provide application of a kalman transformation of the first and second pitch angle control output signals to provide the one or more control signals for cyclic independent pitch control of blades of the wind turbine.

10. A controller according to any preceding claim, wherein the controller is configured to:

11. The controller of any one of claims 1 to 9, wherein the controller is configured to:

12. A controller according to any preceding claim, wherein the controller is configured to:

Calculating a maximum IPC pitch angle IPC _max based on a difference between the uniform pitch reference angle β _coll and the minimum uniform pitch angle β _opt, wherein:

IPC _max＝f(β_coll-β_opt); and

13. The controller of claim 12, wherein the controller is configured to:

14. A controller according to any preceding claim, wherein the determination of the first and second pitch angle control output signals is based on an average wind direction over a last period of time derived from the wind direction information.

15. The controller of claim 1, wherein the controller is configured to provide the predetermined phase shift and a second predetermined phase shift referred to as a first predetermined phase shift, wherein the controller is configured to provide the one or more control signals for implementing cyclic IPC based on the first and second pitch angle control output signals and the first predetermined phase shift if the wind direction information indicates a wind direction incident on the first side of a wind turbine; and if the wind direction information indicates a wind direction incident on the second side of the wind turbine, the controller provides the one or more control signals for implementing cycle IPC without the first predetermined phase shift but with the second predetermined phase shift based on the first pitch angle control output signal and the second pitch angle control output signal.

16. A wind turbine comprising a controller according to any preceding claim.

17. A method for providing cyclic independent pitch control of blades of a wind turbine, the method comprising:

18. A computer program product comprising computer program code configured to provide the method of claim 17 when executed by a processor having a memory.