CN110867894A - Dynamic frequency division wind power generation system with autonomous inertia response - Google Patents
Dynamic frequency division wind power generation system with autonomous inertia response Download PDFInfo
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Abstract
The invention relates to an autonomous inertia response dynamic frequency division wind power generation system, which comprises a wind power plant, a wind power plant step-up transformer, a low-frequency alternating current transmission line, a transmission step-down transformer, a wound rotor asynchronous motor, an electrically excited synchronous motor, an excitation system and a control unit thereof, a coupling unit, a double alternating current port frequency converter, a frequency converter controller, a grid-connected device, a switch device, a step-down transformer, a starting resistor, a detection unit and a central controller, compared with the prior art, the invention adopts the synchronous motor in an isolation type frequency conversion transformer as a power grid interface, so that the whole system presents the characteristics of a synchronous generator to the power grid, the system is favorable for stable operation of the system, in addition, after the whole system is started, the wound rotor asynchronous motor provides concentrated frequency conversion for the wind power plant under the control of the double alternating current frequency converter, and simultaneously drags the electrically excited, under the cooperation of the excitation system and the control unit thereof, the excitation system has the characteristic of power grid friendliness.
Description
Technical Field
The invention relates to the technical field of wind power generation, in particular to a dynamic frequency division wind power generation system with autonomous inertia response.
Background
In the existing common wind power grid-connected control technology, a wind turbine generator does not reflect inertia to a power grid, so that the equivalent inertia of a power system is reduced, and the system stability is not facilitated. The existing improvement measures participate in system frequency response by adding droop control or adopt virtual synchronous machine control to simulate the external characteristics of the synchronous machine.
The most similar realization scheme of the invention is a scheme of adopting a synchronous motor in a rotary frequency-division transformer as the centralized frequency conversion of the whole wind power plant, wherein the rotating speed of the synchronous motor is controlled by a wound rotor motor coupled with the synchronous motor.
In the prior art, a power grid interface part of the whole centralized variable frequency wind power system is a wound rotor motor in an isolated variable frequency transformer, the wound rotor motor is controlled by a back-to-back converter, an adopted control algorithm is vector control of stator voltage orientation, and the characteristic of a current source is essentially reflected to a power grid. Therefore, the whole wind power plant in the scheme is a large-capacity double-fed unit for the power grid, and still cannot provide active support for the power grid.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide the dynamic frequency division wind power generation system with autonomous inertia response.
The purpose of the invention can be realized by the following technical scheme:
a dynamic frequency division wind power generation system with autonomous inertia response comprises a wind power plant, a wind power plant step-up transformer, a low-frequency alternating current transmission line, a transmission step-down transformer, a wound rotor asynchronous motor, an electrically excited synchronous motor, an excitation system and a control unit thereof, a coupling unit, a double alternating current port frequency converter, a frequency converter controller, a grid-connected device, a plurality of switching devices, a step-down transformer, a starting resistor, a detection unit and a central controller, wherein the wind power plant is connected with a stator winding of the wound rotor asynchronous motor sequentially through the wind power plant step-up transformer, the low-frequency alternating current transmission line, the transmission step-down transformer, a first switching device and the detection unit, the first switching device and the detection unit are connected with one end alternating current port of the double alternating current port frequency converter through a fourth switching device, the wind-powered asynchronous motor comprises a wind-wound rotor asynchronous motor, a starting resistor, a double-alternating-current-port frequency converter, a coupling unit, a starting resistor, a central controller and an excitation system, wherein a rotor winding of the wind-wound rotor asynchronous motor passes through the second switching device and the third switching device respectively, the switching device is correspondingly connected with an alternating-current port at one end of the double-alternating-current-port frequency converter, a rotating shaft of the wind-wound rotor asynchronous motor is also connected with a rotating shaft of the electrically-excited synchronous motor through the coupling unit, a stator winding of the electrically-excited synchronous motor passes through the coupling unit and is connected to a power grid, an alternating-current port at the other end of the double-alternating-current-port frequency converter passes through the fifth switching device and is connected to the power grid after passing through the step-down transformer, and the.
Further, the calculation formula of the center frequency of the power transmission frequency range of the system is as follows:
in the formula (f)centralFor the centre frequency, p, of the transmission frequency rangeEESGIs the number of pole pairs, f, of the electrically excited synchronous machine1nFor the rated frequency, p, of the networkWRIMIs the pole pair number of the wound rotor asynchronous motor,
is between 2 and 4.
Further, the variation range of the transmission frequency of the system is as follows:
fL≤fs≤fs_N
in the formula (f)LTo lower limit of transmission frequency, fL≥0.7fcentral，fs_NFor transmission frequencyRated value, fs_N≤1.3fcentral，fsIs the transmission frequency.
Further, the relationship that the wind turbine generator in the wind power plant of the system needs to meet is described by the formula:
in the formula, ngbFor the gear ratio, p, of the wind turbine gearboxWGIs the number of pole pairs, omega, of the generator of the wind turbine generatortnThe rated rotating speed of the wind turbine.
Furthermore, the relation that the wound rotor asynchronous motor of the system needs to satisfy is described by the formula:
in the formula of Us_NRated voltage, U, for said wound rotor asynchronous machines_WG_NRated voltage for wind turbine generator, N1Representing the transformation ratio of the wind farm step-up transformer, N2Representing the transformation ratio of said transmission step-down transformer.
Further, the control method of the frequency converter controller in the wind farm starting mode and the wind farm normal power generation mode comprises the following steps:
step 1: the frequency converter controller receives the three-phase voltage and current from the detection unit to obtain the instantaneous active power P flowing into the stator winding of the wound rotor asynchronous motoreAnd simultaneously obtaining power loss P by backstepping according to three-phase current and circuit, mechanical loss in the wind turbine generator and generator parameterslossΣAnd calculating the ideal reference frequency of the stator winding of the wound rotor asynchronous motor
Step 2:
obtaining the ideal reference frequency of the stator winding of the wound rotor asynchronous motor after amplitude limiting by an amplitude limiter
Wherein the lower limit of the limiter is fLThe upper limit of the limiter is fHWhen the frequency converter controller operates in a wind farm start mode, fH＝fL(ii) a When the frequency converter controller operates in a normal power generation mode of the wind power plant, fH＝fs_N；
And step 3: f. ofs *Subtracting fs0Obtaining the reference frequency f of the rotor winding of the wound rotor asynchronous motorr *When the wind farm is operated in a maximum power tracking mode,
wherein ω isWRIMThe rotating speed of the wound rotor asynchronous motor is set; when the wind farm is in steady state operation in the maximum power tracking mode when the grid frequency is stable,
wherein f is1nRated frequency for the power grid;
and 4, step 4: according to fr *Multiplying by 2 pi and then performing integral operation to obtain the reference phase angle of the voltage of the rotor winding of the wound rotor asynchronous motor
According to fs *Multiplying by Us_N/fs_NObtaining ideal reference voltage of the stator winding of the wound rotor asynchronous motor
And further compensating the voltage drop of the transmission line to obtain the reference voltage of the stator winding of the wound rotor asynchronous motor
And 5: after the three-phase voltage of the stator winding of the wound rotor asynchronous motor obtained through detection is subjected to phase-locked loop and coordinate transformation from a three-phase static coordinate system to a two-phase rotating coordinate system, the effective value U of the voltage of the stator winding of the wound rotor asynchronous motor is further obtained through calculations；
Step 6:
and UsThe deviation of the voltage is output to the rotor winding reference voltage of the wound rotor asynchronous motor through a PI regulator
And 7:
and
obtaining the three-phase voltage reference value of the wound rotor asynchronous motor rotor winding through coordinate transformation
And generating a three-phase voltage reference value of the rotor winding of the wound rotor asynchronous motor at an alternating current port at one end of the double-alternating-current-port frequency converter, and generating driving pulses of a power switching device in the double-alternating-current-port frequency converter by a pulse width modulation module in the frequency converter controller.
Further, the ideal reference frequency of the stator winding of the wound rotor asynchronous motor in the step 1
The calculation formula is as follows:
in the formula, n is the wind turbine set platform in normal power generation operation at presentNumber, koptIs a coefficient determined by the wind turbine parameters, and
wherein rho is air density, R is wind turbine blade radius, CpmaxIs the maximum wind energy utilization coefficient of the wind turbine, lambdaoptThe optimal tip speed ratio of the wind turbine is obtained.
Further, the reference value of the three-phase voltage of the rotor winding of the wound rotor asynchronous motor in the step 7
The calculation formula is as follows:
further, the grid-connected starting method of the electrically excited synchronous motor in the system comprises the following steps:
step 1: the central controller receives a wind speed signal from the wind power plant and judges whether the wind speed meets the starting condition of the wind power plant;
step 2: when the wind speed is judged to accord with the starting condition, a starting program is triggered, the central controller issues on-off instructions for each switch device, the first switch device and the third switch device are disconnected, and the second switch device, the fourth switch device and the fifth switch device are closed;
and step 3: the central controller sends a grid-connected starting mode signal to the frequency converter controller, the frequency converter controller controls the wound rotor asynchronous motor to drag the electrically excited synchronous motor to rotate through the double-alternating-current port frequency converter, and the rotating speed reference value of the wound rotor asynchronous motor is set as the synchronous rotating speed of the electrically excited synchronous motor
f1Is the grid frequency;
and 4, step 4: when the rotating speed of the electrically excited synchronous motor is stabilized at the synchronous rotating speed, the central controller issues an excitation system enabling signal and a voltage reference signal for the excitation system and a control unit thereof, and controls the voltage amplitude of the stator end of the electrically excited synchronous motor to be the same as the voltage amplitude of a power grid;
and 5: the frequency converter controller adjusts the stator terminal voltage phase of the electrically excited synchronous motor according to the phase difference angle fed back by the grid-connected device, and when the stator terminal voltage phase of the electrically excited synchronous motor is the same as or smaller than a set value with the voltage phase of a power grid, the frequency converter controller issues a grid-connected instruction for the grid-connected device, and simultaneously locks a control pulse sent to the double-alternating-current-port frequency converter;
step 6: and the central controller disconnects the second and fourth switching devices, so that the grid-connected starting of the electrically excited synchronous motor is completed, and simultaneously, the states of all the switching devices are kept continuing to the starting and running control process of the wind power plant.
Further, the method for controlling the starting and the operation of the wind power plant in the system comprises the following steps:
step 1: the central controller closes the first and third switch devices and sends a wind power plant starting mode signal to the frequency converter controller, and the frequency converter controller executes control according to a control strategy when the frequency converter controller operates in a wind power plant starting mode and simultaneously keeps the states of all the switch devices at the time;
step 2: the central controller sends a starting instruction to a single wind turbine generator in the wind power plant, and the wind turbine generator stabilizes the rotating speed of the wind turbine generator in the wind power plant through variable pitch control after receiving the instruction
The wind turbine generator is connected to the system through switching on of a switch;
and step 3: the variable pitch control logic of the wind turbine generator is switched to a power generation operation mode, the wind turbine generator is started and completed after a plurality of seconds after the switching command is executed by default, and then the wind turbine generator sends a starting completion handshake signal and a turbine state signal to the central controller;
and 4, step 4: after receiving a starting completion handshake signal and a unit state signal returned by the wind turbine, the central controller switches the corresponding operation mode of the frequency converter controller to a normal power generation mode of the wind power plant, and the frequency converter controller dynamically updates the number of the wind turbine which is in normal power generation operation;
and 5: and the central controller sends a starting instruction to another wind turbine in the wind power plant, the wind turbine returns to execute the step 2 and the step 3 to finish starting, and the rest is done in a further sequence until all the wind turbines in the wind power plant are started.
Compared with the prior art, the invention has the following advantages:
(1) the invention discloses a centralized variable frequency division wind power system with an autonomous synchronization characteristic, wherein an isolation type variable frequency transformer is used for carrying out centralized variable frequency on a wind power plant, so that each single wind power unit does not need to be provided with a frequency converter;
(2) the electric excitation synchronous motor in the system is directly merged into a power grid, and can automatically respond to the power grid requirement similar to a conventional generator set in a power system;
(3) the stator winding of the wound rotor asynchronous motor under the control of the power electronic converter is connected with the wind power plant in the system, so that the system has strong control flexibility and is convenient for function expansion;
(4) in the system, the mode selector S1 in the frequency converter controller is simply set to be 2, so that the whole wind power plant can autonomously participate in the frequency response of the power grid.
(5) The invention comprises a starting process and an operation control method of the dynamic frequency division wind power generation system. After the whole system is started, the wound rotor asynchronous motor provides concentrated frequency conversion for the wind power plant under the control of the double-port alternating-current frequency converter, meanwhile, the gathered wind power plant electric energy is used for dragging the electrically excited synchronous motor to run at a synchronous rotating speed, and under the cooperation of the excitation system and the control unit thereof, the whole system has the characteristic of a conventional synchronous generator for a power grid and has the characteristic of being friendly to the power grid.
Drawings
FIG. 1 is a schematic diagram of a system of the present invention;
FIG. 2 is a control strategy diagram of the inverter controller of the present invention;
FIG. 3 is a schematic diagram of results of wind speed, wind turbine speed and active power in simulation results according to an embodiment of the present invention;
FIG. 4 is a diagram illustrating results of effective values of power transmission frequency, power transmission voltage, rotor frequency of a wound rotor asynchronous motor and rotor voltage of a wound rotor asynchronous motor in simulation results according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a three-phase voltage result of a wound rotor asynchronous motor rotor in a simulation result of an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.
Examples
The embodiment of the invention comprises an integral system scheme, a starting method and a maximum power tracking control method for accessing a wind power plant into a power grid through an isolated variable frequency transformer.
A first part: dynamic frequency division wind power generation system overall scheme with autonomous synchronization characteristic
An autonomous inertia responsive dynamic frequency-division wind power generation system, as shown in fig. 1, comprising:
1) the wind power plant is composed of a plurality of wind turbine generators and a power collection line.
The wind power generation sets do not contain power electronic frequency converters, the generators of the wind power generation sets adopt medium-voltage generators (the typical rated voltage is 6.6 kV-20 kV), and squirrel cage induction generators, permanent magnet synchronous generators, electric excitation synchronous generators and permanent magnet synchronous generators with starting windings can be adopted. When a squirrel-cage induction generator is adopted, a capacitor bank connected in parallel on a stator winding of the generator is also included. The wind turbine generator needs to adopt a position-rotating speed-current three-ring control variable pitch technology and a yaw technology.
The current collecting circuit is used for connecting all wind turbine generators to form a wind power plant, and the existing mature scheme can be adopted.
2) The wind power plant step-up transformer is used for raising the voltage of the wind power plant to the voltage level of low-frequency alternating current transmission and is required to normally work within the frequency and voltage range;
3) the low-frequency alternating current transmission line transmits alternating current with the frequency lower than the power frequency and dynamically changing within a certain range, and the typical working frequency range is 10-16 Hz;
4) the power transmission step-down transformer is used for matching the low-frequency alternating current power transmission with the voltage level of the stator winding of the wound rotor asynchronous motor;
5) the wound rotor asynchronous motor comprises two electrical interfaces of a stator winding and a rotor winding, and a mechanical interface of a rotating shaft;
6) the electrically excited synchronous motor comprises three interfaces of a stator winding, an excitation winding and a mechanical rotating shaft;
7) the excitation system and the control unit thereof have the same functions as those of a conventional thermal generator set or a conventional hydroelectric generator set, and mature technology can be adopted;
8) the coupling unit may further include a speed change gear box, but the speed change gear box is not used in the embodiment of the present invention. This is easily supplemented by the skilled person;
9) the double-alternating-current port frequency converter comprises an alternating-current port 1 and an alternating-current port 2. Two types of ac-to-ac converters (including cycloconverters and matrix converters) or ac-to-dc-to-ac converters may be employed;
10) the frequency converter controller adopts a control strategy matched with the type of the double-AC port frequency converter to complete the starting control and the operation control of the whole system;
11) the grid-connected device is used for reducing grid-connected impact of the electrically excited synchronous motor in the starting process and can adopt a mature technology;
12) a switching device configured as needed;
13) the step-down transformer is used for reducing the voltage grade of the double-alternating-current port frequency converter, is an optional component, and is N3When 1, the equipment is not needed.
14) The starting resistor is used for starting the wound rotor asynchronous motor;
15) the detection unit comprises a voltage sensor, a current sensor and an operation unit, and can detect the three-phase voltage, the current, the active power and the voltage effective value of the stator winding of the wound rotor asynchronous motor;
16) and the central controller is used for coordinating the control of each part.
The parts and their interconnection are described below: a low-voltage side winding of a boosting transformer of the wind power plant is connected with the wind power plant, and a high-voltage side of the boosting transformer of the wind power plant is connected with a low-frequency alternating-current transmission line; the high-voltage side of the transmission step-down transformer is connected with a low-frequency alternating-current transmission line, and the low-voltage side of the transmission step-down transformer is connected with a stator winding of the wound rotor asynchronous motor through a switch device T1; the rotor winding of the wound rotor asynchronous motor is connected with a starting resistor through a switch device T2 and is connected with an alternating current port 2 of the double-port alternating current frequency converter through a T3; the AC port 2 of the dual-port AC frequency converter is also connected to the stator winding of the wound rotor asynchronous motor through a switching device T4; the AC port 1 of the dual-port AC frequency converter is connected to a power grid through a switching device T5 and the low-voltage side of a step-down transformer; the coupler is connected with a winding rotor asynchronous motor rotating shaft and an electrically excited synchronous motor rotating shaft; the excitation winding of the electric excitation synchronous motor is connected with an excitation system and a control unit thereof, and the stator winding of the electric excitation synchronous motor is connected to a power grid through a grid-connected device.
The central controller receives ① superior instructions, ② wind speed, start completion handshake signals and unit state signals from a wind power plant, the realized functions are that ① provides on/off signals for each switch device, ② provides control mode signals and unit state signals for the frequency converter controller, ③ provides start instructions for the wind power plant, and ④ provides excitation system enable and voltage/reactive instructions for an excitation system and a control unit thereof.
The frequency converter controller receives ① control mode signals and unit state signals of a central control unit, ② stator winding three-phase voltage, three-phase current and rotor winding three-phase current of a wound rotor asynchronous motor of a detection unit, ③ whole step phase angle difference of a grid connection device and ④ rotating speed signals of the wound rotor asynchronous motor, and the frequency converter controller has the realization functions of ① providing grid connection instructions for the grid connection device and ② providing control pulses for a double-alternating-current-port frequency converter.
A second part: parameter requirements for part type selection of system
The parameter requirements of the model selection of each part of the system are as follows:
the center frequency of the power transmission frequency range is:
in the formula (f)centralFor the centre frequency, p, of the transmission frequency rangeEESGIs the number of pole pairs, f, of the electrically excited synchronous machine1nFor the rated frequency, p, of the networkWRIMIs the pole pair number of the wound rotor asynchronous motor,
the suggested value of (a) is 3 or 4.
The variation range of the transmission frequency is as follows:
fL1＝0.7fcentral≤fs≤1.3fcentral＝fs_N
in the formula (f)L1To lower limit of transmission frequency, fs_NFor transmission frequencyRated value, fsFor the transmission frequency, each relevant device needs to be able to operate normally in this frequency range.
The relation that the wind turbine generator in the wind power plant of the system needs to meet is described by the following formula:
in the formula, ngbFor the gear ratio, p, of the wind turbine gearboxWGIs the number of pole pairs, omega, of the generator of the wind turbine generatortnThe rated rotating speed of the wind turbine.
The relation that this system wound rotor asynchronous machine needs to satisfy, its description formula is:
in the formula of Us_NRated voltage, U, for said wound rotor asynchronous machines_WG_NRated voltage for wind turbine generator, N1Representing the transformation ratio of the wind farm step-up transformer, N2Representing the transformation ratio of said transmission step-down transformer.
And a third part: the control strategy of the frequency converter controller is as follows:
the frequency converter controller has three control modes, namely an electrically excited synchronous motor grid-connected starting mode, a wind power plant starting mode and a wind power plant normal power generation mode. The grid-connected starting mode of the electrically excited synchronous motor can adopt classical vector control, and the control strategies of the frequency converter controller in the latter two modes are shown in fig. 2.
The frequency converter controller receives the three-phase voltage and current from the detection unit and calculates to obtain the instantaneous active power P flowing into the stator winding of the wound rotor asynchronous motoreAnd calculating the power loss P by backstepping according to the three-phase current, the circuit, the mechanical loss in the wind turbine generator and the generator parameterlossΣCalculating the ideal reference frequency of the stator winding of the wound rotor asynchronous motor according to the following formula
In the formula, n is the number of the wind turbine generators which are in normal power generation operation at present, and koptIs a coefficient determined by the wind turbine parameters, and
wherein rho is air density, R is wind turbine blade radius, CpmaxIs the maximum wind energy utilization coefficient of the wind turbine, lambdaoptThe optimal tip speed ratio of the wind turbine is obtained.
fs *Subtracting fs0Obtaining the reference frequency f of the rotor winding of the wound rotor asynchronous motorr *Wherein f iss0Two given modes are selected according to the maximum power tracking/autonomous inertia response mode of the wind power plant. When mode selector S1When the wind power plant is set to 1, the wind power plant works in a maximum power tracking mode, and at the moment
Wherein ω isWRIMThe rotating speed of the wound rotor asynchronous motor is set; when mode selector S1When the power grid frequency is set to be 2, the wind power plant stably works in a maximum power tracking mode when the power grid frequency is stable, and can autonomously work in an inertia response mode when the power grid frequency is disturbed so as to actively provide dynamic support for the power grid, and at the moment, the wind power plant can actively work in an inertia response mode when the power grid frequency is disturbed
Wherein f is1nThe rated frequency of the power grid.
fr *Multiplying by 2 pi and then performing integral operation to obtain the reference phase angle of the voltage of the rotor winding of the wound rotor asynchronous motor
fs *Multiplying by Us_N/fs_NObtaining ideal reference voltage of stator winding of wound rotor asynchronous motor
Adding the voltage drop from the stator winding of the wound rotor asynchronous motor to the stator winding of the generator of the wind turbine
Obtaining the reference voltage of the stator winding of the wound rotor asynchronous motor
Wherein
The calculation of (a) needs to take into account the translation of the voltage across the transformer.
The three-phase voltage of the stator winding of the wound rotor asynchronous motor obtained by detection is subjected to phase-locked loop and coordinate transformation from a three-phase static coordinate system to a two-phase rotating coordinate system to obtain Usd、UsqFurther by
Calculating to obtain the effective value U of the voltage of the stator winding of the wound rotor asynchronous motors。
when the double-AC port frequency converter adopts an AC-DC-AC frequency converter, the AC port 1 and the AC port 2 are isolated through an intermediate DC link and are relatively independent, at the moment, the control strategy only forms the control of the AC port 2, and the control strategy of the frequency converter controller also comprises the control of the AC port 1. In this case, the control of the ac port 1 is performed with the intermediate dc link voltage constant as the control target, and the existing mature vector control technique can be adopted.
The fourth part: grid-connected starting method for electrically excited synchronous motor
The first step is as follows: the central controller receives a wind speed signal from the wind power plant and judges whether the wind speed meets the starting condition of the wind power plant.
The second step is that: when the wind speed is judged to meet the starting condition, a starting program is triggered, the central controller issues on-off instructions for each switch device, the switch devices T1 and T3 are disconnected, and the switch devices T5, T2 and T4 are closed;
the third step: the central controller sends a grid-connected starting mode signal to the frequency converter controller, and the frequency converter controller controls the wound rotor asynchronous motor to drag the electrically excited synchronous motor to rotate through the double-alternating-current-port frequency converterIn turn, the reference value for the rotational speed of the wound-rotor asynchronous machine is set to the synchronous rotational speed of the electrically excited synchronous machine
f1To the grid frequency, pEESGIs the pole pair number of the electrically excited synchronous motor.
The fourth step: when the rotating speed of the electric excitation synchronous motor is stabilized at the synchronous rotating speed, the central controller issues an excitation system enabling signal and a voltage reference signal for the excitation system and the control unit thereof, and controls the voltage amplitude of the stator end of the electric excitation synchronous motor to be the same as the voltage amplitude of the power grid.
The fifth step: and the frequency converter controller adjusts the stator terminal voltage phase of the electrically excited synchronous motor according to the phase difference angle fed back by the grid-connected device. When the voltage phase of the stator end of the electrically excited synchronous motor is the same as or sufficiently small than the voltage phase of a power grid, the frequency converter controller issues a grid-connected instruction for the grid-connected device, and simultaneously, the frequency converter controller blocks the control pulse sent to the double-AC-port frequency converter.
And a sixth step: the central controller disconnects T2, T4. And finishing the grid-connected starting of the electrically excited synchronous motor.
The fifth part is that: starting and operation control method for wind power plant
The first step is as follows: the central controller closes T3, T1, then sends a windfarm start mode signal to the frequency converter controller (S)21). The frequency converter controller performs control according to fig. 2.
The second step is that: the central controller sends a start instruction to the wind turbine generator 1. Stabilizing the rotating speed in the wind turbine generator set through variable pitch control after receiving instructions
And then the wind turbine generator is connected to a current collection network through switch closing.
The third step: and the wind turbine generator pitch control is switched to a power generation operation mode (at the moment, the wind turbine generator pitch angle acts only when the power or the rotating speed exceeds a rated value), and the wind turbine generator is started and finished 10s after the switching command is executed by default. And then the wind turbine generator sends a starting completion handshake signal and a generator state signal to the central controller, and the generator state signal is set to be 1 when all the components of the generator operate normally.
The fourth step: and after receiving the starting completion handshake signal and the set state signal returned by the wind turbine generator 1, the central controller switches the frequency converter controller to a normal power generation mode of the wind power plant, and dynamically updates the number n of the wind turbine generators with the set state signal of 1.
The fifth step: the central controller sends a starting instruction to the wind turbine generator 2, and the wind turbine generator 2 executes the second step and the third step to complete starting. And repeating the steps until the starting of all the wind turbines in the wind power plant is finished.
All technical features described in the invention have been verified by simulation. Is limited by only one 1.5MW wind turbine generator in a wind power plant with computing resources, the rated frequency of a generator in the wind turbine generator is 16Hz, the rated voltage is 10kV, a wind power plant step-up transformer and a transmission step-down transformer are not adopted (namely the transformation ratio N of the transformer is adopted)1＝1，N21). The wind speed step change is set, and the simulation result is shown in fig. 3, fig. 4 and fig. 5. In the designed power generation operation control mode of the frequency converter controller, the wind turbine generator realizes variable speed operation and maximum power tracking, the power transmission frequency dynamically changes in the designed frequency range, and frequency division power transmission is realized. The amplitude and the frequency of the winding voltage of the rotor of the wound rotor asynchronous motor accord with expectations, and the designed dynamic frequency division wind power generation system works well.
While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications and substitutions can be easily made by those skilled in the art within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. A dynamic frequency division wind power generation system with autonomous inertia response is characterized by comprising a wind power plant, a wind power plant step-up transformer, a low-frequency alternating-current transmission line, a transmission step-down transformer, a wound rotor asynchronous motor, an electrically excited synchronous motor, an excitation system and a control unit thereof, a coupling unit, a double alternating-current port frequency converter, a frequency converter controller, a grid-connected device, a plurality of switching devices, a step-down transformer, a starting resistor, a detection unit and a central controller, wherein the wind power plant is connected with a stator winding of the wound rotor asynchronous motor through the wind power plant step-up transformer, the low-frequency alternating-current transmission line, the transmission step-down transformer, a first switching device and the detection unit in sequence, the first switching device and the detection unit are connected with one end alternating-current port of the double alternating-current port frequency converter through a fourth switching device, the wind-powered asynchronous motor comprises a wind-wound rotor asynchronous motor, a starting resistor, a double-alternating-current-port frequency converter, a coupling unit, a starting resistor, a central controller and an excitation system and a control unit thereof, wherein a rotor winding of the wind-wound rotor asynchronous motor respectively passes through a second switching device and a third switching device and is correspondingly connected with an alternating-current port at one end of the double-alternating-current-port frequency converter, a rotating shaft of the wind-wound rotor asynchronous motor is also connected with a rotating shaft of the electrically-excited synchronous motor through the coupling unit, a stator winding of the electrically-excited synchronous motor passes through the coupling unit and is connected to a power grid, an alternating-current port at the other end of the double-alternating-current-port frequency converter passes through a fifth switching device and is connected to the power grid after passing through a step.
2. The system of claim 1, wherein the center frequency of the transmission frequency range of the system is calculated by the formula:
in the formula (f)centralFor the centre frequency, p, of the transmission frequency rangeEESGIs the number of pole pairs, f, of the electrically excited synchronous machine1nFor the rated frequency, p, of the networkWRIMIs the pole pair number of the wound rotor asynchronous motor,
is between 2 and 4.
3. The system of claim 1, wherein the system has a transmission frequency that varies over a range of:
fL≤fs≤fs_N
in the formula (f)LTo lower limit of transmission frequency, fL≥0.7fcentral，fs_NRated value for transmission frequency, fs_N≤1.3fcentral，fsIs the transmission frequency.
4. The autonomous inertia response dynamic frequency division wind power generation system according to claim 1, wherein the relationship that the wind turbines in the wind farm of the system need to satisfy is described by the formula:
in the formula, ngbFor the gear ratio, p, of the wind turbine gearboxWGIs the number of pole pairs, omega, of the generator of the wind turbine generatortnThe rated rotating speed of the wind turbine.
5. The wind power generation system with autonomous inertia response and dynamic frequency division as claimed in claim 1, wherein the system is characterized in that the wound rotor asynchronous motor satisfies the following relation:
in the formula of Us_NRated voltage, U, for said wound rotor asynchronous machines_WG_NRated voltage for wind turbine generator, N1Representing the transformation ratio of the wind farm step-up transformer, N2Representing the transformation ratio of said transmission step-down transformer.
6. The system of claim 1, wherein the method for controlling the frequency converter controller in the wind farm startup mode and the wind farm normal power generation mode comprises the following sub-steps:
step 1: the frequency converter controller receives the three-phase voltage and current from the detection unit to obtain the instantaneous active power P flowing into the stator winding of the wound rotor asynchronous motoreAnd simultaneously obtaining power loss P by backstepping according to three-phase current and circuit, mechanical loss in the wind turbine generator and generator parameterslossΣAnd calculating the ideal reference frequency of the stator winding of the wound rotor asynchronous motor
Step 2:
obtaining the ideal reference frequency f of the stator winding of the wound rotor asynchronous motor after amplitude limiting by the amplitude limiters *Wherein the lower limit of the limiter is fLThe upper limit of the limiter is fHWhen the frequency converter controller operates in a wind farm start mode, fH＝fL(ii) a When the frequency converter controller operates in a normal power generation mode of the wind power plant, fH＝fs_N；
And step 3: f. ofs *Subtracting fs0Obtaining the reference frequency f of the rotor winding of the wound rotor asynchronous motorr *When the wind farm is operated in a maximum power tracking mode,
wherein ω isWRIMThe rotating speed of the wound rotor asynchronous motor is set; when the wind farm is in steady state operation in the maximum power tracking mode when the grid frequency is stable,
wherein f is1nRated frequency for the power grid;
and 4, step 4: according to fr *Multiplying by 2 pi and then performing integral operation to obtain the reference phase angle of the voltage of the rotor winding of the wound rotor asynchronous motor
According to fs *Multiplying by Us_N/fs_NObtaining ideal reference voltage of the stator winding of the wound rotor asynchronous motor
And further compensating the voltage drop of the transmission line to obtain the reference voltage of the stator winding of the wound rotor asynchronous motor
And 5: after the three-phase voltage of the stator winding of the wound rotor asynchronous motor obtained through detection is subjected to phase-locked loop and coordinate transformation from a three-phase static coordinate system to a two-phase rotating coordinate system, the effective value U of the voltage of the stator winding of the wound rotor asynchronous motor is further obtained through calculations；
Step 6:
and UsThe deviation of the voltage is output to the rotor winding reference voltage of the wound rotor asynchronous motor through a PI regulator
And 7:
and
obtaining the three-phase voltage reference value of the wound rotor asynchronous motor rotor winding through coordinate transformation
And generating a three-phase voltage reference value of the rotor winding of the wound rotor asynchronous motor at an alternating current port at one end of the double-alternating-current-port frequency converter, and generating driving pulses of a power switching device in the double-alternating-current-port frequency converter by a pulse width modulation module in the frequency converter controller.
7. The autonomous inertia response dynamic frequency-division wind power generation system of claim 6, wherein the ideal reference frequency of the stator winding of the wound rotor asynchronous motor in step 1 is set as the reference frequency
The calculation formula is as follows:
in the formula, n is the number of the wind turbine generators which are in normal power generation operation at present, and koptIs a coefficient determined by the wind turbine parameters, and
wherein rho is air density, R is wind turbine blade radius, CpmaxIs the maximum wind energy utilization coefficient of the wind turbine, lambdaoptThe optimal tip speed ratio of the wind turbine is obtained.
8. The autonomous inertia response dynamic frequency division wind power generation system of claim 6, wherein the reference value of the three-phase voltage of the rotor winding of the wound rotor asynchronous motor in the step 7
The calculation formula is as follows:
9. the system of claim 1, wherein the method for starting the electrically excited synchronous machine in a grid-connected mode comprises the following steps:
step 1: the central controller receives a wind speed signal from the wind power plant and judges whether the wind speed meets the starting condition of the wind power plant;
step 2: when the wind speed is judged to accord with the starting condition, a starting program is triggered, the central controller issues on-off instructions for each switch device, the first switch device and the third switch device are disconnected, and the second switch device, the fourth switch device and the fifth switch device are closed;
and step 3: the central controller sends a grid-connected starting mode signal to the frequency converter controller, the frequency converter controller controls the wound rotor asynchronous motor to drag the electrically excited synchronous motor to rotate through the double-alternating-current port frequency converter, and the rotating speed reference value of the wound rotor asynchronous motor is set as the synchronous rotating speed of the electrically excited synchronous motor
f1Is the grid frequency;
and 4, step 4: when the rotating speed of the electrically excited synchronous motor is stabilized at the synchronous rotating speed, the central controller issues an excitation system enabling signal and a voltage reference signal for the excitation system and a control unit thereof, and controls the voltage amplitude of the stator end of the electrically excited synchronous motor to be the same as the voltage amplitude of a power grid;
and 5: the frequency converter controller adjusts the stator terminal voltage phase of the electrically excited synchronous motor according to the phase difference angle fed back by the grid-connected device, and when the stator terminal voltage phase of the electrically excited synchronous motor is the same as or smaller than a set value with the voltage phase of a power grid, the frequency converter controller issues a grid-connected instruction for the grid-connected device, and simultaneously locks a control pulse sent to the double-alternating-current-port frequency converter;
step 6: and the central controller disconnects the second and fourth switching devices, so that the grid-connected starting of the electrically excited synchronous motor is completed, and simultaneously, the states of all the switching devices are kept continuing to the starting and running control process of the wind power plant.
10. The system of claim 1, wherein the method for controlling the start-up and operation of the wind farm in the system comprises the following steps:
step 1: the central controller closes the first and third switch devices and sends a wind power plant starting mode signal to the frequency converter controller, and the frequency converter controller executes control according to a control strategy when the frequency converter controller operates in a wind power plant starting mode and simultaneously keeps the states of all the switch devices at the time;
step 2: the central controller sends a starting instruction to a single wind turbine generator in the wind power plant, and the wind turbine generator stabilizes the rotating speed of the wind turbine generator in the wind power plant through variable pitch control after receiving the instruction
The wind turbine generator is connected to the system through switching on of a switch;
and step 3: the variable pitch control logic of the wind turbine generator is switched to a power generation operation mode, the wind turbine generator is started and completed after a plurality of seconds after the switching command is executed by default, and then the wind turbine generator sends a starting completion handshake signal and a turbine state signal to the central controller;
and 4, step 4: after receiving a starting completion handshake signal and a unit state signal returned by the wind turbine, the central controller switches the corresponding operation mode of the frequency converter controller to a normal power generation mode of the wind power plant, and the frequency converter controller dynamically updates the number of the wind turbine which is in normal power generation operation;
and 5: and the central controller sends a starting instruction to another wind turbine in the wind power plant, the wind turbine returns to execute the step 2 and the step 3 to finish starting, and the rest is done in a further sequence until all the wind turbines in the wind power plant are started.
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| CN113839398A (en) * | 2021-08-31 | 2021-12-24 | 国网江苏电力设计咨询有限公司 | Variable droop coefficient control method for double-fed fan participating in primary frequency modulation of power grid |
| CN113839398B (en) * | 2021-08-31 | 2023-08-25 | 国网江苏电力设计咨询有限公司 | Variable droop coefficient control method for double-fed fans participating in primary frequency modulation of power grid |
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