GB2538750A

GB2538750A - Method of determining a wind speed and a braking torque of a wind turbine

Info

Publication number: GB2538750A
Application number: GB1509067.3A
Authority: GB
Inventors: Parsons David
Original assignee: ECOTRICITY GROUP Ltd
Current assignee: ECOTRICITY GROUP Ltd
Priority date: 2015-05-27
Filing date: 2015-05-27
Publication date: 2016-11-30
Anticipated expiration: 2035-05-27
Also published as: GB201509067D0; GB2538750B

Abstract

A method of determining the wind speed acting on a wind turbine 10 in comparison to a wind speed threshold. The wind turbine comprises a rotor and a brake configured to vary the speed of the rotor. The method includes the steps of; controlling the brake to vary the speed of the rotor; determining a resulting acceleration; and determining that the wind speed is more than or less than the threshold based on the determined acceleration. Also disclosed is an apparatus and a computer program for performing the above method with a controller 100. The comparison of the calculated wind velocity may be compared to the high or low wind speed shutdown thresholds. Also claimed is a method, an apparatus and a computer programme measuring the breaking torque of a turbine by controlling the brake.

Description

METHOD OF DETERMINING A WIND SPEED AND A BRAKING TORQUE OF A WIND TURBINE

Field

This disclosure relates to determining a wind speed and braking torque of a wind turbine. More particularly, this disclosure discloses embodiments that relate to determining that a wind speed of wind acting on a wind turbine is more than or less than a wind speed threshold and/or determining that a braking torque of a brake associated with a wind turbine is more than or less than a braking torque threshold.

Background

Wind turbines commonly rely on brakes to regulate the wind turbine speed, in particular the speed of the rotor. Such regulation may be necessary when the power available from the wind is higher than that required to produce maximum useable power from the wind turbine. It may also be necessary to regulate the wind turbine speed to lessen the stress and fatigue on the parts of the wind turbine in high power winds.

In very high power winds, it may typically be necessary to shut-down the wind turbine altogether, in which case the brake is used to bring the rotor to a stop. It is therefore important to be able to detect when the wind power exceeds such a shut-down threshold so that the wind turbine can be safely shut-down.

The brake may be used to stop the wind turbine for other reasons (for example, maintenance). The brake may also hold the rotor in a stopped position until such time that it is suitable to start the wind turbine again.

Typically, wind speed is treated as indicative of the power available from the wind. Wind speed is commonly measured using anemometers. In some approaches, anemometers may be connected to, or near, the wind turbine. This can result in the wind speed readings being unreliable due to obstructions and turbulence effects of the wind turbine structure itself. In other approaches, anemometers may be positioned at a location remote from the wind turbine with the wind speed at the wind turbine having to be estimated. However, due to the lack of uniformity of wind speed over a certain area (due to, for example, naturally occurring wind speed gradients or the effects of obstructions) it can be difficult to obtain accurate wind speed measurements at the wind turbine itself.

Such inaccurate readings are undesirable as they may lead to the wind turbine being shut-down in wind speeds that are, in fact, less than the intended shut-down wind speed. This can result in an unnecessary loss of electricity power generation. Inaccurate readings may also lead to the wind turbine remaining operational in wind speeds that are, in fact, more than the intended shut-down wind speed. This can result in higher than expected stress and fatigue on the wind turbine or over-speed of the rotor.

Another difficulty arises due to the delay in measuring and averaging wind speed measurements. This may lead to a delay in engaging the brake upon detecting a high wind speed, increasing the potential for over-speed of the rotor.

A further difficulty arises due to the shut-down of the wind turbine being dependent on readings from anemometers. Anemometers are relatively sensitive and may not be fail-safe. A fault in an anemometer may affect the reliability and safety of the shut-down of the wind turbine.

Yet another difficulty arises from treating wind speed (as measured by anemometers) as indicative of the power available from the wind. In addition to wind speed, wind power is dependent upon other variables such as the atmospheric conditions (for example, temperature and humidity) or the type of flow (for example, turbulent or skewed flow). Changes in these other variables may alter the wind speed at which the wind turbine can or should be safely shut-down, reducing safety margins unacceptably. Anemometers may not be able to detect changes in these other variables.

An object of at least certain embodiments of the present disclosure is to address one or more of these problems.

Summary of the Invention

According to one aspect there is provided a method of determining that a wind speed of wind acting on a wind turbine is more than or less than a wind speed threshold, wherein the wind turbine comprises a rotor configured to rotate in response to the wind and a brake configured to vary the speed of the rotor, including the steps of: controlling the brake such that the brake varies the speed of the rotor; determining a resulting acceleration of the rotor; and determining that the wind speed is more than or less than the wind speed threshold based on the determined acceleration of the rotor.

The wind speed threshold may be the wind speed more than which an aspect of the operation of the wind turbine may be controlled. The speed of the rotor may be varied, the wind turbine may be shut down, the wind turbine may be started up or power may be provided, at least partly, to the rotor. The wind speed threshold may be the wind speed less than an aspect of the operation of the wind turbine may be controlled. The speed of the rotor may be varied, the wind turbine may be shut-down, the wind turbine may be started up or power may be provided, at least partly, to the rotor. In certain embodiments, the wind speed threshold may be the wind speed more than which the wind turbine is shut-down.

The wind speed threshold may be set based on the operating parameters of the wind turbine and/or the characteristics of its location. The wind speed threshold may be adjusted based on changes in the operating parameters of the wind turbine and/or the characteristics of its location. The wind speed threshold may be stored in a memory accessible by a controller. The wind speed threshold may be stored in the memory either upon manufacture or by a user using a suitable interface configured to connect with the controller.

The step of determining that the wind speed is more than or less than the wind speed threshold based on the determined acceleration of the rotor may include determining that the determined acceleration is more than or less than an acceleration threshold. The acceleration threshold may comprise a first acceleration threshold. The step of determining that the wind speed is more than or less than the wind speed threshold based on the determined acceleration of the rotor may include determining that the determined acceleration is negative and has a magnitude less than a first acceleration threshold. This can be used to indicate excess wind speed. The acceleration threshold may comprise a second acceleration threshold. The step of determining that the wind speed is more than or less than a wind speed threshold based on the determined acceleration of the rotor may include determining that the determined acceleration is positive and has a magnitude greater than a second acceleration threshold. This can be used to indicate excess wind speed. The step of determining that the wind speed is more than or less than the wind speed threshold based on the determined acceleration of the rotor may be carried out by the controller.

The acceleration threshold may be related to the magnitude of the wind speed threshold and whether the method is being used to determine that the wind speed is either more than or less than the wind speed threshold. The acceleration threshold may be set based on the operating parameters of the wind turbine and/or the characteristics of its location. The acceleration threshold may be adjusted based on changes in the operating parameters of the wind turbine and/or the characteristics of its location. The acceleration threshold may be stored in the memory accessible by the controller. The acceleration threshold may be stored in the memory either upon manufacture or by a user using the suitable interface.

The method may include the step of determining the speed of the rotor. This may include determining the speed of a shaft of the rotor. The step of determining the speed of the rotor may include sensing a parameter indicative of the rotational speed of the rotor. The data indicative of the sensed parameter may be provided to the controller. The controller may determine the speed based on the data.

The step of controlling the brake such that the brake varies the speed of the rotor may include applying the brake. Applying the brake may result in the speed of the rotor decreasing. The step of controlling the brake such that the brake varies the speed of the rotor may include releasing the brake. Releasing the brake may result in the speed of the rotor increasing. The brake may be in one of two states: either applied or released. The speed of the rotor may be varied to maintain the speed of the rotor less than a certain speed. The speed of the rotor may be varied for the purpose of determining that the wind speed is more than or less than the wind speed threshold. The speed of the rotor may be varied for some other reason.

The method may include the further step of detecting that the speed of the rotor reaches a first threshold. The speed of the rotor reaching the first threshold may be detected by the controller. Upon detecting that the speed of the rotor reaches a first threshold, the brake may be controlled so as to cause the brake to vary the speed of the rotor. The method may include the further step of detecting that the speed of the rotor reaches a second threshold. The speed of the rotor reaching the second threshold may be detected by the controller. Upon detecting that the speed of the rotor reaches a second threshold, the brake may be controlled so as to cause the brake to vary the speed of the rotor. The first threshold and/or second threshold may be set based on the operating parameters, ratings and safety margins of the wind turbine and/or the characteristics of its location. The first threshold and/or second threshold may be adjusted based on changes in the operating parameters of the wind turbine and/or the characteristics of its location.

The step of determining the resulting acceleration of the rotor may include sensing a parameter indicative of the acceleration of the rotor from which the acceleration can be determined. The controller may determine the resulting acceleration based on the data indicative of the sensed parameter. The step of determining the resulting acceleration of the rotor may include determining the rate of change of the rotor speed, for example, by measuring the time taken for the rotor speed to change from the first threshold to the second threshold and thus determining the rate.

The method may include the further step of, upon determining that the wind speed is more than or less than a wind speed threshold performing a further action. The controller may produce an output to effect the further action. The further action may be controlling the brake to bring the rotor to a stop. The controller may produce an output to apply the brake until the rotor is stopped. The further action may be generating an alert. The controller may generate an alert.

In a further aspect, there is provided a wind turbine comprising a rotor, a brake configured to vary the speed of the rotor, and a controller, wherein the controller is configured to: control the brake such that the brake varies the speed of the rotor; determine a resulting acceleration of the rotor; and determine that a wind speed of wind acting on the wind turbine is more than or less than a wind speed threshold based on the determined acceleration of the rotor.

The wind turbine may be a vertical axis wind turbine wherein the axis of rotation of the rotor is substantially perpendicular to the ground. The wind turbine may be a horizontal axis wind turbine wherein the axis of rotation of the rotor is substantially parallel to the plane of the ground. The rotor may comprise a suitable number of blades connected to a shaft. The shaft may be connected to a generator such that rotation of the shaft causes electricity to be generated by the generator.

The brake may be a brake that exhibits constant braking torque and is independent from the wind. For example, the brake may be a friction brake or an electrodynamic brake. Such an electrodynamic brake may consist of a large bank of resistors that can be selectively connected to the inverter or the generator. The brake may be connected to the controller such that outputs produced by the controller control the brake. The brake may be in one of two states: either applied or released.

The controller may be configured to control the operation of the wind turbine. The controller may include a CPU or other suitable device. The controller may be programmed with a computer program comprising code portions. The controller may be configured to receive inputs from various components of the wind turbine. The controller may be configured to produce outputs that control the operation of various components of the wind turbine, such as, for example, the brake. The controller may be configured to connect to an interface. The interface may be used by a user so as to monitor or modify the controller. The controller may connect to the interface over a wired or wireless connection. The controller may comprise a memory in which variables associated with the operation of the wind turbine may be stored. In particular, the memory may store variables associated with the methods described herein, including: the wind speed threshold; the acceleration threshold; the first threshold; and the second threshold. The variables may be stored on the memory by a user using the interface.

The wind turbine may further include a rotor speed sensor. The rotor speed sensor may be configured to determine the speed of the rotor or shaft. The rotor speed sensor may sense a parameter indicative of rotor speed. The rotor speed sensor may be connected to the controller, providing rotor speed data to the controller. The rotor speed sensor may provide data indicative of the sensed speed to the controller from which the rotor speed may be determined by the controller.

In addition to determining wind speed, it is also necessary to ensure the brake has sufficient braking torque to regulate the rotor speed and -of particular importance from a safety standpoint -shutting down the wind turbine in very high power wind. The brake can degrade over time depending on the brake used. This may lead to a reduction or complete failure in the ability of the brake to slow the rotor. It is therefore desirable to detect a reduction in the ability of the brake to slow the rotor so that necessary maintenance can be undertaken.

In another aspect there is provided a method of determining that a braking torque of a brake associated with a wind turbine is more than or less than a braking torque threshold, wherein the wind turbine comprises a rotor configured to rotate in response to wind and the brake is configured to vary the speed of the rotor, including the steps of: controlling the brake such that the brake varies the speed of the rotor, determining a resulting acceleration of the rotor, determining the wind speed at the wind turbine, and determining that the braking torque is more than or less than the braking torque threshold based on the determined acceleration of the rotor and the determined wind speed at the wind turbine.

The braking torque threshold may be the braking torque more than which some operation may be performed. The brake may be inspected or have maintenance conducted upon it. The braking torque threshold may be the braking torque less than which some operation may be performed. The brake may be inspected or have maintenance conducted upon it.

The braking torque threshold may be set based on the operating parameters of the wind turbine and/or the characteristics of the brake. The braking torque threshold may be stored in a memory accessible by a controller. The braking torque threshold may be stored in the memory either upon manufacture or by a user using a suitable interface configured to connect with the controller.

The step of determining that the braking torque is more than or less than the braking torque threshold based on the determined acceleration of the rotor and the determined wind speed at the wind turbine may include determining that the determined acceleration is more than or less than an acceleration threshold and determining that the determined wind speed is more than or less than a wind speed threshold. The acceleration threshold may comprise a first acceleration threshold and the wind speed threshold may comprise a first wind speed threshold. The step of determining that the braking torque is less than the braking torque threshold based on the determined acceleration of the rotor and determined wind speed at the wind turbine may include determining that the magnitude of the determined acceleration is less than a first acceleration threshold and determining that the magnitude of the determined wind speed is less than a first wind speed threshold. This may be used to indicate insufficient braking torque. The step of determining that the braking torque is more than or less than the braking torque threshold based on the determined acceleration of the rotor and the determined wind speed at the wind turbine may be carried out by the controller.

The acceleration threshold and the wind speed threshold are related to the magnitude of the braking torque threshold and whether the method is being used to determine that the braking torque is either more than or less than the braking torque threshold. The acceleration threshold may be dependent on the determined wind speed or the wind speed threshold may be dependent on the determined acceleration. The acceleration threshold and wind speed threshold may be set based on the operating parameters of the wind turbine and/or the characteristics of the brake. The acceleration threshold and wind speed threshold may be adjusted based on changes in the operating parameters of the wind turbine and/or the characteristics of its location. The acceleration threshold and wind speed threshold may be stored in the memory accessible by the controller. The acceleration threshold and wind speed threshold may be stored in the memory either upon manufacture or by a user using the suitable interface.

The method may include the further step of establishing the acceleration threshold based on the determined wind speed. The step of determining that the braking torque is more than or less than a braking torque threshold based on the determined acceleration of the rotor and the determined wind speed at the wind turbine may include determining that the determined acceleration is more than or less than the established acceleration threshold. The step of determining that the braking torque is less than a braking torque threshold may include determining that the magnitude of the determined acceleration is less than the established acceleration threshold. This may be used to indicate insufficient braking torque.

The step of controlling the brake such that the brake varies the speed of the rotor may include applying the brake. Applying the brake may result in the speed of the rotor decreasing. The step of controlling the brake such that the brake varies the speed of the rotor may include releasing the brake. Releasing the brake may result in the speed of the rotor increasing. The brake may be in one of two states: either applied or released. The speed of the rotor may be varied to maintain the speed of the rotor less than a certain speed. The speed of the rotor may be varied for the purpose of determining that the braking torque is more than or less than the braking torque threshold. The speed of the rotor may be varied for some other reason.

The method may include the further step of detecting that the speed of the rotor reaches a first threshold. The speed of the rotor reaching the first threshold may be detected by the controller. Upon detecting that the speed of the rotor reaches a first threshold, the brake may be controlled so as cause the brake to vary the speed of the rotor. The method may include the further step of detecting that the speed of the rotor reaches a second threshold. The speed of the rotor reaching the second threshold may be detected by the controller. Upon detecting that the speed of the rotor reaches a second threshold, the brake may be controlled so as cause the brake to vary the speed of the rotor. The first threshold and/or second threshold may be set based on the operating parameters, ratings and safety margins of the wind turbine and/or the characteristics of its location. The first threshold and/or second threshold may be adjusted based on changes in the operating parameters of the wind turbine and/or the characteristics of its location.

The step of determining the wind speed at the wind turbine may include sensing a parameter indicative of the wind speed from which the wind speed at the wind turbine may be determined. The controller may determine the wind speed based on the data.

The method may include the further step of, upon determining that the braking torque is more than or less than a braking torque threshold performing a further action. The controller may produce an output to effect the further action. The further action may be controlling the brake to bring the rotor to a stop. The controller may produce an output to apply the brake until the rotor is stopped. The further action may be generating an alert. The controller may generate an alert.

In a further aspect, there is provided a wind turbine comprising a rotor, a brake configured to vary the speed of the rotor, and a controller, wherein the controller is configured to: control the brake such that the brake varies the speed of the rotor; determine a resulting acceleration of the rotor; determine a wind speed at the wind turbine; and determine that a braking torque is more than or less than a braking torque threshold based on the determined acceleration of the rotor and the determined wind speed at the wind turbine.

The brake may be a brake that is independent from the wind. For example, the brake may be a friction brake or an electrodynamic brake. Such an electrodynamic brake may consist of a large bank of resistors that can be selectively connected to the inverter or the generator. The brake may be connected to the controller such that outputs produced by the controller control the brake. The brake may be in one of two states: either applied or released.

The controller may be configured to control the operation of the wind turbine. The controller may include a CPU or other suitable device. The controller may be programmed with a computer program comprising code portions. The controller may be configured to receive inputs from various components of the wind turbine. The controller may be configured to produce outputs that control the operation of various components of the wind turbine, such as, for example, the brake. The controller may be configured to connect to an interface. The interface may be used by a user so as to monitor or modify the controller. The controller may connect to the interface over a wired or wireless connection. The controller may comprise a memory in which variables associated with the operation of the wind turbine may be stored. In particular, the memory may store variables associated with the methods described herein, including: the braking torque threshold; the wind speed threshold; the acceleration threshold; the first threshold; and the second threshold. The variables may be stored on the memory by a user using the interface.

The wind turbine may further include a wind speed sensor. The wind speed sensor may be configured to determine the wind speed at the wind turbine. The wind speed sensor may sense a parameter indicative of wind speed. The wind speed sensor may be connected to the controller, providing wind speed data to the controller. The wind speed sensor may provide data indicative of the sensed wind speed to the controller from which the wind speed may be determined by the controller. The controller may be connected to, alternatively or in addition, a further wind speed sensor. The further wind speed turbine may be configured to determine the wind speed at a position remote from the wind turbine. The further wind speed sensor may sense a parameter indicative of wind speed. The further wind speed sensor may provide data to the controller from which the wind speed at the wind turbine may be determined by the controller.

Reference to any prior art in this specification does not constitute an admission that such prior art forms part of the common general knowledge.

Brief Description of the Drawings

Specific embodiments will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 shows an isometric view of a wind turbine suitable for use with the methods of

the present disclosure;

Figure 2 shows a block diagram representing the wind turbine of Figure 1; Figure 3 shows a graph representing a possible relationship between Rotor Speed and Wind Speed for the wind turbine of Figure land Figure 2; Figure 4 shows a flow chart for a method of determining that wind speed is more than or less than a wind speed threshold according to a general embodiment; Figure 5 shows a flow chart a method of determining that wind speed is more than or less than a wind speed threshold according to a specific embodiment of the method described in relation to Figure 4; Figure 6 shows a flow chart for a method of determining that a braking torque is more than or less than a braking torque threshold according to a general embodiment; Figure 7 shows a flow chart for a method of determining that a braking torque is more than or less than a braking torque threshold according to a specific embodiment of the method described in relation to Figure 6; and Figure 8 shows a flow chart for a method determining that a braking torque is more than or less than a braking torque threshold according to another specific embodiment of the method described in relation to Figure 6.

Detailed Description

Referring to Figure 1, there is shown an embodiment of a wind turbine 10. The wind turbine is a vertical axis turbine, with the axis of rotation 20 being substantially perpendicular to the ground (not shown). The wind turbine includes a mast 30. At the end of the mast furthest from the ground, there is a rotor 40 (not shown in Figure 1). Generally, the rotor is configured to rotate about the axis of rotation 20 in response to wind acting on the wind turbine. Though vertical axis turbines may generate power regardless of the wind direction, they can experience increased stress and fatigue due to the reversal of forces every rotation of the rotor.

The rotor 40 includes a number of blades 50 connected to a shaft 60 by an arrangement of struts 70 connected to a hub 80, which in turn is connected to the shaft. As will be appreciated, the blades are shaped such that wind moving past the wind turbine 10 will cause the blades to move and thus cause the rotor 40 to rotate about the axis of rotation 20 in response to the wind. The axis of rotation corresponds to the shaft 60.

The shaft 60 is connected to a generator 90. Rotation of the rotor 40 (and correspondingly, the shaft) causes electricity to be generated by the generator. The generator is further connected to an inverter (not shown in Figure 1), which conditions the generated electricity and provides it to an electricity distribution network (not shown in Figure 1) such that the generated electricity may be used. Alternatively, the power may be used to charge batteries, provide heating or pump fluids.

The wind turbine 10 also includes a controller 100. The controller is configured to control various aspects of the operation of the wind turbine including aspects related to the methods of the present disclosure. The controller may include a CPU or other suitable device (or a combination thereof). The controller is configured to receive inputs from various components of the wind turbine. The controller is also configured to produce outputs that control the operation of various components of the wind turbine. The controller may comprise a memory in which may be stored variables associated with the operation of the wind turbine. In particular, the memory may store variables associated with the methods described herein, including: the wind speed threshold, the acceleration threshold, the first threshold and the second threshold.

The wind turbine 10 also includes a wind speed sensor 110. The wind speed sensor is an anemometer. The wind speed sensor is connected to the mast 30. The anemometer senses the wind speed at the wind turbine. As will be appreciated, the power of wind acting on a wind turbine is, at least partly, dependent on the wind speed. Thus, for the purposes of this description, the wind speed of wind acting on the wind turbine may be understood to be the speed of the wind at the wind turbine, wherein such wind does -or has the potential to -transfer energy to the wind turbine. The wind speed sensor provides wind speed data to the controller 100.

Figure 2 shows a block diagram representing the wind turbine 10. As described in relation to Figure 1, the wind turbine includes the rotor 40, comprising blades 50 connected to the shaft 60 by an arrangement of struts 70 connected to the hub 80. The shaft is further connected to the generator 90. Though the shaft is shown in Figure 2 as being distinct from the generator, it will be appreciated that it is equally accurate to consider the shaft as part of the generator. When there is sufficient wind 120 to generate power (ie the so-called 'cut-in' wind speed), the shaft rotates inside the generator 120, causing electricity to be generated by the generator, which in turn is conditioned by an inverter 140 and supplied to the electricity distribution network 130. Alternatively, the power may be used to charge batteries, provide heating or pump fluids.

Figure 2 also shows a brake 150. In this embodiment, the brake is an electrodynamic brake. The electrodynamic brake includes of a large bank of high power resistors 160 that can be selectively connected in parallel to the inverter 140 (for example, by a suitable arrangement of switches). It will be appreciated that upon switching in the large bank of high power resistors, the load seen by the inverter increases significantly and therefore more current is drawn from the generator 90. This results in an increase in the magnetic force opposing the rotation of the shaft 60 in the generator. Thus the electrodynamic brake 150, when applied, exerts a force to oppose rotation of the rotor 40 and hence tends to decrease the speed of the rotor 40. The electrodynamic brake is shown in Figure 2 as connected to the inverter, yet distinct from the inverter and generator. However it will be appreciated that it is also appropriate to consider the brake as including the inverter and generator as these components act in conjunction with the bank of resistors to achieve the braking effect. The braking torque of the electrodynamic brake is independent of the wind. In embodiments where the brake is another type of brake (for example, a friction brake), it will be appreciated that the brake may be understood to act upon or work in conjunction with a different component or components of the wind turbine (for example, a friction brake may be configured to act upon the shaft 60). The brake may be in one of two states: either applied or released. The brake 150 is connected to the controller 100. The controller is configured to produce outputs that control the operation of the brake. This can include outputs that either apply or release the brake. Though the controller 100 is shown in Figure 2 as a single component, it will be appreciated that the controller may also be configured as a combination of separate controllers, each configured to control a subset of various aspects of the operation of the wind turbine. The separate controllers may be distributed in various parts of the wind turbine.

However, for the sake of simplicity, for the remainder of this description the controller will be referred to as a single component.

The controller 100 is connected to a rotor speed sensor 170 such that rotor speed data may be provided from the rotor speed sensor to the controller as an input. For the purposes of this description, rotor speed (or speed of the rotor) may be understood to mean the angular speed of the rotor as it rotates about its axis of rotation. The rotor speed sensor determines the speed of the rotation of the shaft 60 (and thus the speed of the rotor 40). The shaft 40 includes a number of elements (not shown in Figure 2) spaced at regular intervals circumferentially about the shaft.

For example, the elements may be bolt heads. The rotor speed sensor inductively senses each element as it passes. The rotor speed sensor may then determine the speed based on the angular distance and the time taken between elements. Alternatively, the rotor speed may be determined by the controller 100 based on the data provided to the controller from the rotor speed sensor. It will be appreciated that the number and spacing of elements will affect the frequency of data points and therefore the precision of the determined speed. The rotor speed data produced by the rotor speed sensor is provided as an input to the controller. As will be discussed in more detail below, the controller may use the rotor speed data for various steps of the method of the present disclosure, including determining the rotor speed (in embodiments where the rotor speed sensor does not, itself, determine the rotor speed), detecting that the rotor speed has reached a certain threshold, or determining the resulting acceleration of the rotor. Other possible approaches to determine the rotor speed may include sensing the frequency of the generated electricity or sensing the voltage of an associated tachogenerator. The rotor speed may then be determined by the controller based on this sensed data. The rotor speed sensor 170 is shown in Figure 2 as associated with the shaft 60, however in embodiments where the rotor speed sensor is another type of sensor, it will be appreciated that the rotor speed sensor may be associated with a different component of the wind turbine (for example, a suitable sensor associated with the inverter for sensing the frequency of the generated electricity).

The controller 100 is connected to a wind speed sensor 110. The wind speed sensor is an anemometer 110, which senses the wind speed and provides wind speed data as an input to the controller. The controller may also be connected to further wind speed sensors 180. Such further wind speed sensors may be positioned at a location or locations remote from the wind turbine 10. As will be discussed in more detail below, the controller may use this wind speed data provided by the wind speed sensor 110 and further wind speed sensors 180 for various steps of the method of the present disclosure, including for example determining the wind speed. For example, the controller may be configured to determine wind speed at the wind turbine based on the sensed data, such as, determining the wind speed based on the wind speed sensed by an anemometer remote from the wind turbine.

In addition to determining the rotor speed and determining the wind speed, the controller also determines the resulting acceleration of the rotor. The controller may determine the resulting acceleration of the rotor by determining the rate of change of the rotor speed. In some embodiments, it may be possible to use the same rotor speed data as described above and determine acceleration based on how the rotor speed varies over time.

The controller 100 is also connected to an interface 190. The interface provides a means for a user to monitor and modify the operation of the controller (and thus monitor and modify the operation of the wind turbine 10). The interface may include a screen configured to display various alerts that may be output by the controller. The interface may be connected to the controller over a wired or wireless connection. The interface may be used to store the variables associated with the methods described herein on the memory accessible by the controller.

Operation of the wind turbine 10 will now be described.

Figure 3 shows a graph 200 representing a relationship between Rotor Speed and Wind Speed for the wind turbine 10 of Figure land Figure 2. It should be noted that the graph is for illustrative purposes, and the actual relationship will depend on the operating parameters of the wind turbine and/or the characteristics of its location.

For wind speeds less than a cut-in wind speed 210, the wind turbine is shut-down. The wind turbine is kept shut-down by applying the brake 150, thus preventing the rotor 40 from rotating in response to the wind. The wind speed is determined by the wind speed sensor 110 and/or further wind speed sensors 180. Alternatively, the wind speed may be determined by the controller 100 based on data provided to the controller from the wind speed sensor 110 and/or further wind speed sensors 180. When the controller 100 detects that the wind speed (as determined by the wind speed sensor or the controller itself) reaches the cut-in wind speed 210, the controller permits or causes the turbine to start rotating. The cut-in wind-speed 210 may be stored in the memory accessible by the controller 100 via the interface 190.

As the wind speed increases, the rotor speed increases (as indicated by arrow 220) and correspondingly, the power generated by the wind turbine also increases. The rotor speed is determined by rotor speed sensor 170. Alternatively, the rotor speed may be determined by the controller 100 based on data provided to the controller from the rotor speed sensor 170. When the controller 100 detects that the rotor speed (as determined by the rotor speed sensor or the controller itself) reaches a first threshold 230, the controller controls the brake by producing an output that causes the brake to vary the speed of the rotor. That is to say, the controller produces an output to apply the brake and to decrease the speed of the rotor. Then, when the controller detects that the rotor speed (as determined by the rotor speed sensor or the controller itself) reaches a second threshold 240, the controller controls the brake by producing an output that causes the brake to vary the speed of the rotor. That is to say, the controller produces an output to release the brake and to enable the speed of the rotor to increase. Then, when the rotor speed reaches the first threshold, the brake is again applied as described above. It will thus be appreciated that the rotor speed is regulated to be substantially in the range between the first threshold and the second threshold. The first threshold and second threshold are set based on the operating parameters, ratings and safety margins of the wind turbine and/or the characteristics of its location. In particular, they may be set to ensure power generated by the wind turbine does not exceed a maximum useable amount. The first threshold 230 and second threshold 240 may be stored in the memory accessible by the controller 100 via the interface 190.

As the wind speed increases, the rotor speed will reach the first threshold 230 at a wind speed corresponding to the minimum wind speed 250 at which the maximum useable amount of power can be generated. For wind speeds more than this minimum wind speed 250 and less than a cutoff wind speed 260, the rotor speed is regulated in the range between the first threshold 230 and the second threshold 240. It is in this range that the wind turbine generates the maximum useable amount of power. Over this range of wind speeds, the rotor speed is shown in Figure 3 as a band to illustrate that the rotor speed is regulated between the first threshold 230 and the second threshold 240 according to the approach described above.

When the wind speed reaches the cut-off wind speed 260, it may not be possible or desirable to continue to regulate the speed of the rotor 40 between the first threshold 230 and the second threshold 240. This may be because of increased loads and stresses on the rotor and the wind turbine structure. Therefore, when the controller 100 detects that the wind speed reaches the cut-off wind speed 260, the controller controls the brake 150 to bring the rotor 40 to a stop. As will be appreciated from the methods discussed below, the controller may determine the wind speed indirectly by determining the acceleration of the rotor and thereby detect that the wind speed has reached the cut-off wind speed 260.

Above the cut-off wind speed 260, the wind turbine remains shut-down, thus the rotor speed is zero. When the controller 100 detects the wind speed is less than the cut-off wind speed, the controller releases the brake 150 to enable the rotor to begin rotating again (and for the wind turbine to generate power).

As will be appreciated, the wind speed does not always rise or fall in an orderly manner.

Therefore, the controller 100 may be configured to include a degree of hysteresis or delay so that temporary changes in wind speed (such as a gust or a lull) do not result in unnecessary changes in the operation of the turbine. For example, if the wind turbine has been shut-down due to the wind speed reaching the cut-off wind speed, a decrease in wind speed so as to be less than the cut-off wind speed may not lead to the wind turbine starting up again provided the wind speed remains less than the cut-off wind speed until a suitable delay period has lapsed.

Having provided an overview of a wind turbine and its operation, the methods of the present disclosure can now be described. Though the method will be described in relation to the wind turbine discussed in relation to Figures 1-3, those skilled in the art will appreciate how the methods may be modified to work with other wind turbine configurations.

The acceleration of the rotor of the wind turbine is dependent on the torque acting on the rotor. The torque of the wind acts to increase or maintain the rotor speed, while the braking torque acts to decrease the rotor speed (when the brake is applied). By convention, the torque of the wind acting on a rotor is positive, and the torque of the brake in a wind turbine is either negative (if the brake is applied) or substantially zero (if the brake is released). Thus, the net torque acting on the rotor (ie the sum of the braking torque and the wind torque) dictates the resulting acceleration of the rotor.

As discussed previously, the power of wind acting on a wind turbine is, at least partly, dependent 10 on the wind speed. Thus, the wind torque is dependent on wind speed.

The braking torque associated with the wind turbine may be understood to be the torque of the brake that is able to, or has the potential to, decrease the speed of the rotor. In some scenarios it is helpful to presume that the braking torque does not change over time.

If, for a service life of the wind turbine, the braking torque of the brake is presumed not to change (ie it remains a non-zero value when applied and zero when released), then the braking torque is one of two constants. Conversely, the wind torque is dependent on the wind speed and is therefore a dependent variable. Since the acceleration of the rotor is dependent on the net torque and the braking torque is one of two constants, only changes in the wind torque will affect the acceleration of the rotor (for the brake being either applied or released). Hence, the acceleration of the rotor may be used to indicate the wind torque and therefore the wind speed.

Thus, if the determined acceleration of the rotor is less than or more than an acceleration 25 threshold, this may be used to indicate that the wind speed is more than or less than a wind speed threshold.

There will now be discussed a method for determining that a wind speed of wind acting on a wind turbine is more than or less than a wind speed threshold that takes advantage of the above.

Figure 4 shows a general flow diagram representing the method of determining that the wind speed is more than (or alternatively, less than) the wind speed threshold. The method may be carried out by the controller 100 described above in relation to the wind turbine 10. Any particular embodiment of the method will depend upon the wind speed threshold and whether the method is being used to determine that the wind speed is either more than or less the wind speed threshold. Though it will be described in relation to Figure 4 in a general sense, a more specific embodiment will be described in relation to Figure 5 (wherein the wind speed is more than the cut-off wind speed 260). It will be appreciated that the method may also be adapted to determine other wind speeds, for example, wind speed less than the minimum wind speed 250 at which the maximum useable amount of power can be generated.

In a first step 401, the brake is controlled such that the brake varies the speed of the rotor. The controller generates an output that causes the brake to be applied or released. Upon being applied, the brake will cause the speed of the rotor to decrease. Upon being released, the brake 45 will allow the speed of the rotor to increase.

In a second step 402, the resulting acceleration of the rotor is determined. The resulting acceleration of the rotor is determined as the speed of the rotor is varied by the brake. The resulting acceleration may be determined by the controller in response to rotor speed data 5 provided to the controller from the rotor speed sensor.

In a third step 403, whether the wind speed is more than (or less than) the wind speed threshold is determined by comparing the determined acceleration to the acceleration threshold. The acceleration threshold and the corresponding comparison requirement will depend on the wind speed threshold and whether the method is being used to determine that the wind speed is either more than or less the wind speed threshold. The acceleration threshold and the corresponding comparison requirement may be stored in the memory accessible by the controller via the interface. If the determined acceleration satisfies the comparison requirement, then it is determined that the wind speed is more than (or less than) the wind speed threshold. If the determined acceleration does not satisfy the particular comparison requirement, then it is determined that the wind speed is not more than (or less than) the wind speed threshold.

In a fourth step 404a, if it is determined that the wind speed is more than (or less than) the wind speed threshold, then suitable subsequent actions may be performed. Examples are described in relation to Figure 5.

In an alternative fourth step 404b, if it is determined that the wind speed is not more than (or less than) the wind speed threshold, then suitable subsequent actions may be performed. Examples are described in relation to Figure 5.

Figure 5 shows a flow diagram representing a specific embodiment of the method described in relation to Figure 4. In particular, Figure 5 shows a flow diagram representing a method of determining that the wind speed is more than the cut-off wind speed 260 (as discussed in relation to Figure 3).

In a first step 501, the brake is applied to decrease the rotor speed when the rotor speed reaches the first threshold 230 (as described above in relation to Figure 3). In particular, the controller may detect that the rotor speed has reached the first threshold in response to rotor speed data provided to the controller from the rotor speed sensor. The controller may subsequently generate an output that causes the brake to be applied.

In a second step 502, the resulting acceleration of the rotor is determined by the controller. The resulting acceleration of the rotor is determined as or after the speed of the rotor is decreased by the brake. In one embodiment, the controller may detect that the rotor speed has reached the second threshold 240 in response to rotor speed data provided to the controller from the rotor speed sensor. The controller may determine the acceleration of the rotor by measuring the time taken for the rotor speed to decrease from the first threshold 230 to the second threshold 240 and thus determine the acceleration. Since the speed of the rotor is being decreased, the determined acceleration will be negative.

In a third step 503, whether the wind speed is more than the cut-off wind speed is determined by comparing the determined acceleration to an acceleration threshold. This comprises determining if the magnitude of the determined acceleration is less than the acceleration threshold. If the magnitude of the determined acceleration is less than the acceleration threshold, then it is determined that the wind speed is more than the cut-off wind speed. In other words, since the rotor is decelerating too slowly, it can be deduced that the wind speed is more than the cut-off wind speed 260. If the magnitude of the determined acceleration is more than the acceleration threshold, then it is determined that the wind speed is not more than the cut-off wind speed. In other words, since the rotor is decelerating sufficiently quickly, it can be deduced that the wind speed is less than the cut-off wind speed 260. In this embodiment, the acceleration threshold is set based on the operating parameters of the wind turbine and/or the characteristics of its location.

In a fourth step 504a, if it is determined that the wind speed is more than the cut-off wind speed, 15 then the wind turbine may be shut-down as described previously.

In an alternative fourth step 504b, it is determined that the wind speed is not more than the cut-off wind speed, then the brake may be released to allow the speed of the rotor to increase.

It will thus be appreciated that the wind speed exceeding the cut-off wind speed can be determined without having to rely on anemometers or other wind speed sensors. Further, the method ensures that there is minimal to no delay between an increase in wind speed and detecting the effect on the wind turbine.

The preceding method discussed in relation to Figures 4 and 5 relied on the presumption that the braking torque of the brake does not change. However, the braking torque may be dependent on a number of variables such as the condition of parts of the brake or the presence of defects. It will be understood that as these variables change, so too does the braking torque. Therefore, the braking torque may, in fact, change over time.

Insufficient braking torque, whether caused by degradation, defect or some other cause, may lead to inefficient operation of the wind turbine. It may also present a safety concern should, for example, the wind turbine not be able to be safely shut-down when there is excess wind speed. Similarly, excess braking torque, whether caused by degradation, defect or some other cause, may lead to the wind turbine not operating as intended or may be indicative of some other fault in the brake or the wind turbine more generally.

If, for the service life of the wind turbine, the braking torque of the brake is presumed to change (ie a range of values when applied and/or a range of values when released), then the braking torque is a dependent variable. Similarly, the wind torque is dependent on the wind speed and is also a dependent variable. Since the acceleration of the rotor is dependent on the net torque, changes in both the wind torque and braking torque will affect the acceleration of the rotor (for the brake being either applied or released). Hence, the resulting acceleration of the rotor and the wind torque may be used to indicate the brake torque and therefore the braking torque.

Thus, if the determined acceleration of the rotor is less than or more than an acceleration threshold but the determined wind speed is less than or more than a wind speed threshold, this can be used to indicate that the braking torque is more than or less than a braking torque threshold. Alternatively, since the acceleration is dependent on the wind speed, the acceleration threshold may itself be formulated as a variable dependent on the determined wind speed, and therefore if the determined acceleration of the rotor is less than or more than an acceleration threshold (as varied dependent on the determined wind speed), this can be used to indicate that the braking torque is more than or less than a braking torque threshold. Similarly, since the acceleration is dependent on the wind speed, the wind speed threshold may be formulated as variable dependent on the determined acceleration, and therefore if the determined wind speed is less than or more than a wind speed threshold (as varied dependent on the determined acceleration), this can be used to indicate that the braking torque is more than or less than a braking torque threshold.

There will now be discussed a method for determining that a braking torque of a brake associated with a wind turbine is more than or less than a braking torque threshold that takes advantage of the above.

Figure 6 shows a general flow diagram representing the method of determining that the braking torque is more than (or alternatively, less than) the braking torque threshold. The method may be carried out by the controller 100 described above in relation to the wind turbine 10. Any particular embodiment of the method will depend upon the braking torque threshold and whether the method is being used to determine that the braking torque is either more than or less the braking torque threshold. Though it will be described in relation to Figure Gina general sense, more specific embodiments will be described in relation to Figures 7 and 8 (wherein the braking torque is less than a lower braking torque threshold). It will be appreciated that the method may also be adapted to determine other braking torques, for example, braking torque more than an upper braking torque threshold.

In a first step 601, the brake is controlled such that the brake varies the speed of the rotor. The controller generates an output that causes the brake to be applied or released. Upon being applied, the brake will cause the speed of the rotor to decrease. Upon being released, the brake will allow the speed of the rotor to increase.

In a second step 602, the resulting acceleration of the rotor is determined. The acceleration of the rotor is determined as the speed of the rotor is varied by the brake. The acceleration may be determined by the controller in response to rotor speed data provided to the controller from the rotor speed sensor.

In a third step 603, the wind speed at the wind turbine is determined. It will be appreciated that this third step may also occur before or at the same time as the second step. The wind speed at the wind turbine may be determined by the controller in response to wind speed data provided to the controller from the wind speed sensor or further wind speed sensor.

In a fourth step 604, whether the braking torque is more than (or less than) the braking torque threshold is determined by comparing the determined acceleration and the determined wind speed to the acceleration threshold and wind speed threshold. The comparison requirement will depend on the braking torque threshold and whether the method is being used to determine that the braking torque is either more than or less the braking torque threshold. The acceleration threshold, wind speed threshold and the corresponding comparison requirement may be stored in the memory accessible by the controller via the interface. If the determined acceleration and determined wind speed satisfy the comparison requirement, then it is determined that the braking torque is more than (or less than) the braking torque threshold. If the determined acceleration and determined wind speed do not satisfy the particular comparison requirement, then it is determined that the braking torque is not more than (or less than) the braking torque threshold.

In a fifth step 605a, if it is determined that the braking torque is more than (or less than) the braking torque threshold, then suitable subsequent actions may be performed. Examples are described in relation to Figures 7 and 8.

In an alternative fifth step 605b, if it is determined that the braking torque is more than (or less than) the braking torque threshold, then suitable subsequent actions may be performed.

Examples are described in relation to Figures 7 and 8.

Figure 7 shows a flow diagram representing a specific embodiment of the method described in relation to Figure 6. In particular, Figure 7 shows a flow diagram representing a method of determining that the braking torque is less than a minimum braking torque threshold (ie insufficient braking torque).

In a first step 701, the brake is applied to decrease the rotor speed when the rotor speed reaches the first threshold 230 (as described above in relation to Figure 3).

In a second step 702, the resulting acceleration is determined by the controller. The acceleration of the rotor is determined as the speed of the rotor is decreased by the brake. In one embodiment, the controller may detect that the rotor speed has reached the second threshold 240 in response to rotor speed data provided to the controller from the rotor speed sensor. The controller may determine the acceleration of the rotor by measuring the time taken for the rotor speed to decrease from the first threshold 230 to the second threshold 240. Since the speed of the rotor is being decreased, the determined acceleration will be negative.

In a third step 703, the wind speed at the wind turbine is determined by an anemometer connected to the mast of the wind turbine. It will be appreciated that this third step may also 40 occur before or at the same time as the second step. The determined wind speed is provided to the controller.

In a fourth step 704, whether the braking torque is less than the minimum braking torque threshold is determined by comparing the determined acceleration and the determined wind speed to the acceleration threshold and the wind speed threshold. This comprises determining if the magnitude of the determined acceleration and the determined wind speed are both less than the acceleration threshold and the wind speed threshold respectively. If the magnitude of the determined acceleration and the determined wind speed are both less than the acceleration threshold and the wind speed threshold respectively then it is determined that the braking torque is less than the minimum braking torque threshold. In other words, if the rotor is decelerating slowly (as might otherwise indicate excess wind speed) but the wind speed is less than the cut-off wind speed, it can be deduced that there may be insufficient braking torque. If the magnitude of the determined acceleration and the determined wind speed are not both less than the acceleration threshold and the wind speed threshold respectively, then it is determined that the braking torque is not less than the minimum braking torque threshold. In other words, since the rotor is decelerating sufficiently quickly regardless of the wind speed, it can be deduced that there is sufficient braking torque. In this embodiment, the acceleration threshold and the wind speed threshold are set based on the operating parameters of the wind turbine and/or the characteristics of its location. In this particular embodiment, the acceleration threshold is the cut-off acceleration and the wind speed threshold is the cut-off wind speed 260.

In a fifth step 705a, if it is determined that the braking torque is less than the minimum braking torque threshold, then the wind turbine may be shut-down as described previously and/or an alert may be generated by the controller. The alert may indicate that there is a possible fault with 20 the brake and/or that maintenance needs to be carried out.

In an alternative fifth step 705b, if it is determined that the braking torque is not less than the minimum braking torque threshold, then the brake may be released to allow the speed of the rotor to increase.

Figure 8 shows a flow diagram representing a specific embodiment of the method described in relation to Figure 6. In particular, Figure 8 shows a flow diagram representing a method of determining that the braking torque is less than a minimum braking torque threshold (ie insufficient braking torque).

In a first step 801, the brake is applied to decrease the rotor speed when the rotor speed reaches the first threshold (as described above in relation to Figure 3).

In a second step 802, the resulting acceleration is determined by the controller. The acceleration of the rotor is determined as the speed of the rotor is decreased by the brake. In one embodiment, the controller may detect that the rotor speed has reached the second threshold 240 in response to rotor speed data provided to the controller from the rotor speed sensor. The controller may determine the acceleration of the rotor by measuring the time taken for the rotor speed to decrease from the first threshold to the second threshold. Since the speed of the rotor is being decreased, the determined acceleration will be negative.

In a third step 803, the wind speed at the wind turbine is determined by an anemometer connected to the mast of the wind turbine. It will be appreciated that this third step may also occur before or at the same time as the second step. The determined wind speed is provided to the controller.

In a fourth step 804, the acceleration threshold is established depending on the determined wind speed. In this case, the acceleration threshold has been formulated as a variable dependent on the determined wind speed.

In a fifth step 805, whether the braking torque is less than the minimum braking torque threshold is determined by comparing the determined acceleration to the established acceleration threshold. This comprises determining if the magnitude of the determined acceleration is less than the established acceleration threshold. If the magnitude of the determined acceleration is less than the established acceleration threshold then it is determined that the braking torque is less than the minimum braking torque threshold. In other words, if for the determined wind speed the rotor should decelerate with a minimum rate but the rotor is in fact decelerating more slowly, it can be deduced that there is insufficient braking torque. If the magnitude of the determined acceleration is not less than the established acceleration threshold, then it is determined that the braking torque is not less than the minimum braking torque threshold. In other words, if for the determined wind speed the rotor should decelerate with a minimum rate and the rotor is in fact decelerating at (at least) that minimum rate, it can be deduced that there is sufficient braking torque.

In a sixth step 806a, if is determined that the braking torque is less than the minimum braking torque threshold, then the wind turbine may be shut-down as described previously and/or an alert may be generated by the controller. The alert may indicate that there is a possible fault with the brake and/or that maintenance needs to be carried out.

In an alternative six step 806b, if is determined that the braking torque is not less than the minimum braking torque threshold, then the brake may be released to allow the speed of the rotor to increase.

It will thus be appreciated that the braking torque being less than a desired minimum braking torque threshold can be determined by inference from the acceleration of the rotor. The method ensures that the brake of the wind turbine has sufficient braking torque to stop the rotor if need be. Thus, shutting down the wind turbine at a set acceleration threshold protects against degradation of the brake, by effectively causing the wind turbine to be shut-down at a lower wind speed than the rated cut-off wind speed.