WO2022000898A1

WO2022000898A1 - Method and system for coordinated control of high-voltage ride-through of wind turbine generator set

Info

Publication number: WO2022000898A1
Application number: PCT/CN2020/126630
Authority: WO
Inventors: 孙华东; 赵兵; 王铁柱; 周莹坤; 王姗姗; 徐式蕴; 李文锋
Original assignee: 中国电力科学研究院有限公司; 国家电网有限公司
Priority date: 2020-06-30
Filing date: 2020-11-05
Publication date: 2022-01-06
Also published as: CN111934326A

Abstract

A method and system for the coordinated control of the high-voltage ride-through of a wind turbine generator set, which method and system belong to the technical field of wind power generation control. The method for the coordinated control of the high-voltage ride-through of a wind turbine generator set comprises: performing real-time monitoring on a wind turbine generator set, so as to acquire monitoring information (S10); comparing a generator-end voltage of the wind turbine generator set with a preset voltage threshold value, and comparing the change rate of the generator-end voltage of the wind turbine generator set with a preset change rate threshold value, so as to respectively acquire comparison results (S20); and according to the comparison results, controlling a current transformer and a low-voltage electric reactor of the wind turbine generator set, so as to complete the coordinated control of the high-voltage ride-through of the wind turbine generator set (S30).

Description

Method and system for coordinated control of high voltage ride through of wind turbines

This application claims the priority of the Chinese patent application with application number 202010621095.4 filed with the China Patent Office on June 30, 2020, the entire contents of which are incorporated herein by reference.

technical field

The present disclosure relates to the technical field of wind power generation control, for example, to a method and system for coordinating and controlling high voltage ride through of wind turbines.

Background technique

Large-scale long-distance power transmission is an important measure to solve large-scale clean energy consumption and prevent air pollution, but the characteristics of large-scale clean energy power generation also bring a series of challenges to the safe and stable operation of the power grid, such as the High and low voltage ride-through problems, such as the high-voltage ride-through problem of wind turbines, are difficult to solve, which seriously restricts the security of the power grid and the delivery of new energy.

In recent years, with the continuous increase of the single-unit capacity of wind turbines and the rapid increase in the proportion of the total installed capacity in the power grid, many countries in the world have issued guidelines for grid-connected wind power, and put forward some suggestions on the stability and reliability of grid-connected wind turbines. increasingly stringent requirements. Among them, the more difficult and relatively high technical requirements are the fault ride-through operation under the grid voltage sag or swell fault.

Different from low voltage ride-through, there are few researches and engineering practices on the operation and control of wind turbines under grid voltage swell faults. In recent years, large-scale wind power off-grid accidents and related studies have shown that in the voltage recovery stage after the grid fault is eliminated, the high-voltage lines connected to the wind farm may experience overvoltage, sudden load drop of the wind farm, large capacity The input of the capacitor compensator will also cause a surge in the grid voltage, and then the wind farm will be disconnected from the grid.

When new energy is distributed in areas far away from the load center, large-scale new energy is sent centrally by conventional high voltage or ultra-high voltage direct current. However, due to the problem of commutation failure in UHVDC, and due to the long distance of DC transmission and the relatively wide spanning area, commutation failure occurs from time to time. During the commutation failure, the AC grid will generate a large amount of reactive power surplus, the voltage of the AC bus will rise sharply, and the maximum may reach 1.3pu, and the AC grid wind at the sending end will be disconnected from the grid in a large area; when the DC commutation is restored, the DC power will be reduced. When operation is resumed, the power of the power grid at the sending end will be unbalanced, and the frequency of the system will drop sharply, which may cause a large loss of load, which will have a great impact on the safe operation of the power grid.

There is no effective engineering solution for large-scale wind turbine off-grid caused by power grid disturbance fault (including AC fault and DC fault), which causes large-scale wind turbine to be disconnected from the grid. DC transmission channel capacity is limited.

SUMMARY OF THE INVENTION

The present disclosure provides a method for coordinated control of high voltage ride-through of wind turbines, including:

Perform real-time monitoring on the wind turbine to obtain monitoring information, wherein the monitoring information includes: the terminal voltage of the wind turbine and the rate of change of the terminal voltage of the wind turbine;

Comparing the terminal voltage of the wind turbine with a preset voltage threshold, and comparing the rate of change of the terminal voltage of the wind turbine with the preset threshold of the rate of change, respectively obtaining comparison results;

According to the comparison results, the converters and low-voltage reactors of the wind turbine are controlled to complete the coordinated control of the high-voltage ride-through of the wind turbine.

Also provided is a system for coordinating and controlling high voltage ride-through of wind turbines, including:

a monitoring module, which performs real-time monitoring on the wind turbine and obtains monitoring information, wherein the monitoring information includes: the terminal voltage of the wind turbine and the rate of change of the terminal voltage of the wind turbine;

The comparison module compares the terminal voltage of the wind turbine with a preset voltage threshold, and compares the rate of change of the terminal voltage of the wind turbine with the preset threshold for the rate of change, and obtains comparison results respectively;

The coordinated control module controls the converter and the low-voltage reactor of the wind turbine according to the comparison result, so as to complete the coordinated control of the high voltage ride through of the wind turbine.

Description of drawings

FIG. 1 is a flowchart of a method for coordinating and controlling high voltage ride through of a wind turbine according to an embodiment of the present invention;

2 is a schematic structural diagram of a low-voltage reactor for a method for coordinating and controlling high-voltage ride-through of a wind turbine according to an embodiment of the present invention;

3 is a flowchart of a method for coordinating and controlling high voltage ride-through of a wind turbine according to an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a system for coordinating and controlling high voltage ride through of a wind turbine according to an embodiment of the present invention.

detailed description

Exemplary embodiments of the present disclosure are described below with reference to the accompanying drawings, however, the present disclosure may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for the purpose of illustrating the present disclosure. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present disclosure. In the drawings, the same elements/elements are given the same reference numerals.

Unless otherwise specified, terms (including technical and scientific terms) used herein have their commonly understood meanings. In addition, terms defined in commonly used dictionaries should be construed as having meanings consistent with the context in the related field.

The present disclosure provides a method for coordinated control of high voltage ride through of a wind turbine, as shown in FIG. 1 , including the following steps.

S10. Perform real-time monitoring on the wind turbine to obtain monitoring information.

In an embodiment, the monitoring information includes: the terminal voltage of the wind turbine and the rate of change of the terminal voltage of the wind turbine.

S20. Compare the generator terminal voltage of the wind turbine with a preset voltage threshold, and compare the change rate of the generator terminal voltage of the wind generator with the preset change rate threshold to obtain comparison results respectively.

S30 , controlling the converter and the low-voltage reactor of the wind turbine according to the comparison result, so as to complete the coordinated control of the high voltage ride through of the wind turbine.

In the present disclosure, a low-voltage reactor that can be switched on and off quickly through a thyristor switch is installed at the outlet of the wind turbine, so as to realize the coordination of the reactive power control of the converter and the switching control strategy of the low-voltage reactor, and solve the disturbance fault that occurs in the large power grid. The problem of causing the voltage of the system busbar to rise sharply, which in turn leads to the instantaneous increase of the outlet voltage of the wind turbine in the wind farm and disconnection from the grid, can be applied to all wind power plants, covering a wide range. Compared with the transformation of the wind turbine itself, it is convenient to implement and low investment. , the effect is more significant.

Optionally, the preset voltage threshold includes a first threshold, a second threshold and a third threshold, and the second threshold is greater than the first threshold and the third threshold.

Optionally, the third threshold is less than or equal to the first threshold.

Control the converter of the wind turbine according to the comparison result, including:

When the terminal voltage of the wind turbine is greater than or equal to the first threshold, start the first external controller; and when T is greater than or equal to the delay time of the reactive power control confirmation time of the converter of the wind turbine, control the first external controller The inverter confirms the control command and sends the reactive power start control command to the converter of the wind turbine; after the converter of the wind turbine starts according to the reactive power start control command, the converter of the wind turbine is controlled to absorb inductive reactive power in the grid. .

In an embodiment, T is a time command signal for starting timing when the terminal voltage of the wind turbine reaches or exceeds a preset voltage threshold. The preset voltage threshold may be the first threshold.

Control the low-voltage reactors of wind turbines according to the comparison results, including:

When the terminal voltage of the wind turbine is greater than or equal to the second threshold, the second external controller is activated; and when T is greater than or equal to the delay time of the low-voltage reactor input confirmation time, the second external controller is controlled to confirm the control command and lead to Turn on the thyristor bidirectional switch, put into the low-voltage reactor, and control the low-voltage reactor to absorb inductive reactive power in the power grid.

The second external controller is a thyristor switching based controller.

In an embodiment, the T is a time command signal for starting timing when the terminal voltage of the wind turbine reaches or exceeds the preset voltage threshold.

When the terminal voltage of the wind turbine is less than the third threshold, and the rate of change of the terminal voltage of the wind turbine is less than the preset rate of change threshold, the second external controller is activated; and T is greater than or equal to the LV reactor cutoff confirmation time During the delay time, the second external controller is controlled to confirm the control command, cut off the two-way switch of the thyristor, and control the low-voltage reactor to exit operation, and the T is that the terminal voltage of the wind turbine reaches or exceeds the preset voltage threshold The time command signal to start timing when the second external controller is a controller based on thyristor switching.

The embodiments of the present invention will be described below with reference to the embodiments.

As shown in Figure 2, it is a schematic structural diagram of a low-voltage reactor based on thyristor switch switching. A low-voltage reactor based on thyristor switch switching is installed at the wind turbine end.

The low-voltage reactor based on thyristor switch switching includes: thyristor two-way switch, low-voltage reactor, and control circuit. One end (W) of the thyristor two-way switch is directly connected to the outlet line or bus of the wind turbine, and the other end (S) is directly connected to the low-voltage The reactors are connected in series, one end of the low-voltage reactor is directly connected to the S terminal of the thyristor two-way switch, and the other end is grounded. The control loop is connected to the S and G terminals of the thyristor two-way switch to form a control loop to realize the input and exit of the low-voltage reactor, and the thyristor two-way switch The turn-on (low-voltage reactor input) speed is not more than 10 milliseconds, and the turn-off (low-voltage reactor exit) time of the thyristor bidirectional switch is not more than 50 milliseconds.

As shown in Figure 3, making full use of the fast reactive power control capability of the wind turbine main body converter, and coordinating with the low-voltage reactor to suppress the high voltage at the wind turbine terminal, including the following steps.

Aiming at the problem that the outlet voltage of wind turbines rises instantaneously and exceeds the overvoltage protection setting of wind turbines due to disturbance faults in the large power grid, the coordinated control of wind turbine converters and fast switching reactors is adopted to suppress the problem. Wind turbine port voltage (ie, machine terminal voltage).

Quickly control the converter of the wind turbine. When the voltage rises to a specified threshold, the reactive power control of the converter is quickly activated, so that the converter of the wind turbine absorbs inductive reactive power from the grid.

A reactor with a certain capacity is installed at the outlet of the wind turbine. When the voltage rises to a specified threshold, the reactor is quickly put into use, so that the reactor can absorb inductive reactive power from the grid.

When the terminal voltage of the wind turbine rises sharply, the first external controller preferentially controls the converter, and controls the low-voltage reactor when the voltage of the wind turbine continues to rise. The port voltage remains within a reasonable range that does not trigger protection action.

An external controller is used to jointly control the converter of the wind turbine and the low-voltage reactor installed at the wind turbine end, and the real-time measured voltage of the wind turbine protection voltage transformer (PT) is used as the input of the controller.

A first external controller is set for the converter of the wind turbine. The input of the controller is the measured voltage of the protection PT, and the output of the controller is to directly send reactive power control commands to the inverter. Smooth control of the terminal port voltage. When U≥U _th1 , the reactive power control system of the converter of the wind turbine generator is activated. When T≥T ₁ , the controller confirms the control command and sends reactive power to the converter. The control command realizes smooth control of the terminal voltage of the wind turbine. The entire control process does not exceed 20 milliseconds. U _th1 represents the first threshold of the terminal voltage of the _{wind turbine, and T 1} represents the reactive power control of the converter of the wind turbine. Confirmation time delay.

On the basis of reactive power control performed by the first external controller of the converter of the wind turbine, supplementary control is carried out for the primary equipment installed at the port of the wind turbine—low-voltage reactor, that is, the low-voltage reactor is quickly switched on and off. The second external controller is also provided with the second external controller, and the input of the second external controller is the PT measurement voltage (which can be shared with the input signal of the external controller of the converter of the wind turbine), and the measured voltage at the machine end when the reactive power of the converter is controlled When it continues to rise rapidly and reaches the threshold value, the low-voltage reactor _{is turned on. When U≥U th2} , the second external controller based on thyristor _{switching is activated. When T≥T 2} , the second external controller confirms the control command , turn on the bidirectional switch of the thyristor, and switch on the low-voltage reactor, U _th2 represents the second threshold value of the terminal voltage of the wind turbine, T ₂ represents the confirmation time delay of low-voltage reactor switching, where U _th2 >U _th1 .

When the system disturbance disappears, the system voltage will return to normal. At this time, the input of the low-voltage reactor will cause the system voltage to drop. Therefore, the exit control link needs to be set for the low-voltage reactor.

When U <U _th3, the voltage variation rate K _U <K _th, and that the delay T> T ₃ when started based on the second external controller Thyristor, GTO bidirectional switch, the low pressure quickly exit the reactor operation to ensure that no low voltage occurs after a disturbance.

The switching of the low-voltage reactor will not cause harmonic interference to the wind turbine and the AC power grid. During the operation stage of the low-voltage reactor, the transient voltage of the wind turbine port will not exceed the low-voltage protection action value of the unit, and the port voltage will not be stabilized. The state value is lower than 0.95pu.

For the communication between the external reactive power controller of the converter of the wind turbine and the PT measurement end and the unit converter, a dedicated direct-connected fiber channel needs to be implemented, and the time delay from the PT measurement outlet to the converter receiving the control command No more than 10 milliseconds, and the entire control process does not exceed 20 milliseconds.

For the control system of the low-voltage reactor, the structure of the thyristor two-way switching switch and the reactor in series is adopted, and the thyristor switch is connected in parallel at the outlet of the wind turbine. greater than 10 milliseconds.

The switching of the low-voltage reactor will not cause harmonic interference to the wind turbine and the AC power grid, and will not cause the transient voltage of the wind turbine port to exceed the low-voltage protection action value of the unit during the operation stage of the low-voltage reactor, and will not cause the port voltage. The steady state value is below 0.95pu.

The embodiment of the present invention also proposes a system 200 for coordinating and controlling the high voltage ride through of wind turbines, as shown in FIG. 4 , including the following modules.

The monitoring module 201 is configured to perform real-time monitoring on the wind turbine and obtain monitoring information;

Monitoring information, including: the terminal voltage of the wind turbine and the rate of change of the terminal voltage of the wind turbine;

The comparison module 202 is configured to compare the machine terminal voltage of the wind turbine with a preset voltage threshold, and compare the change rate of the machine end voltage of the wind turbine with the preset change rate threshold, and obtain comparison results respectively;

The coordination control module 203 is configured to control the converter and the low-voltage reactor of the wind turbine according to the comparison result, so as to complete the coordinated control of the high voltage ride through of the wind turbine.

The preset voltage threshold includes a first threshold, a second threshold and a third threshold, and the second threshold is greater than the first threshold and the third threshold.

The coordination control module 203 is set to:

When the terminal voltage of the wind turbine is greater than or equal to the first threshold, start the first external controller; and when T is greater than or equal to the delay time of the reactive power control confirmation time of the converter of the wind turbine, control the first external controller The inverter confirms the control command and sends the reactive power start control command to the converter of the wind turbine; after the converter of the wind turbine starts according to the reactive power start control command, the converter of the wind turbine is controlled to absorb inductive reactive power in the grid. , the T is the time command signal for starting timing when the terminal voltage of the wind turbine reaches or exceeds the preset voltage threshold.

The coordination control module 203 is set to:

When the terminal voltage of the wind turbine is greater than or equal to the second threshold, the second external controller is activated; and when T is greater than or equal to the delay time of the low-voltage reactor input confirmation time, the second external controller is controlled to confirm the control command and lead to Turn on the two-way switch of the thyristor, put in the low-voltage reactor, and control the low-voltage reactor to absorb inductive reactive power in the power grid;

The second external controller is a controller based on thyristor switching, and the T is a time command signal for starting timing when the terminal voltage of the wind turbine reaches or exceeds the preset voltage threshold.

The coordination control module 203 is configured to start the second external controller when the terminal voltage of the wind turbine is less than the third threshold and the rate of change of the terminal voltage of the wind turbine is less than the preset rate of change threshold; and T is greater than When it is equal to the delay time of the low-voltage reactor cut-off confirmation time, the second external controller is controlled to confirm the control command, cut off the thyristor bidirectional switch, and control the low-voltage reactor to exit operation. Or a time command signal for starting timing when the preset voltage threshold is exceeded, and the second external controller is a controller based on thyristor switching.

The present disclosure is aimed at the problem that the wind turbine cluster of tens of millions of kilowatts sent by the UHVDC converter station is sent out centrally due to the sudden rise of the terminal voltage of the wind turbine caused by the failure of the UHV DC commutation, and the wind turbine cluster is disconnected from the grid in a large area. Optimize the reactive power control strategy of the converter of the wind turbine and install a low-voltage reactor at the outlet of the wind turbine that can be switched on and off quickly through the thyristor switch to realize the coordination of the reactive power control of the converter and the switching control strategy of the low-voltage reactor It solves the problem that the system bus voltage suddenly rises due to disturbance faults in the large power grid, which in turn leads to the instantaneous rise of the outlet voltage of the wind turbines in the wind farm and the disconnection from the grid. It can be applied to all wind power plants and has a wide coverage. Compared with the transformation of the wind turbine body, the realization is convenient, the investment is small, and the effect is more significant.

Embodiments of the present application may be provided as methods, systems, or computer program products. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may employ computer-usable storage media (including disk storage, portable Compact Disc Read Only Memory (CD-ROM), optical storage, etc.) having computer-usable program code embodied in one or more of them. in the form of a computer program product implemented thereon. The solutions in the embodiments of the present application may be implemented in various computer languages, for example, the object-oriented programming language Java and the literal translation scripting language JavaScript, and the like.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. Each flow and/or block in the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to the processor of a general purpose computer, special purpose computer, embedded processor or other programmable data processing device to produce a machine such that the instructions executed by the processor of the computer or other programmable data processing device produce Means for implementing the functions specified in a flow or flow of a flowchart and/or a block or blocks of a block diagram.

These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory result in an article of manufacture comprising instruction means, the instructions The apparatus implements the functions specified in the flow or flow of the flowcharts and/or the block or blocks of the block diagrams.

These computer program instructions can also be loaded on a computer or other programmable data processing device to cause a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process such that The instructions provide steps for implementing the functions specified in the flow or blocks of the flowcharts and/or the block or blocks of the block diagrams.

Claims

A method for coordinating and controlling high voltage ride-through of wind turbines, comprising:

Perform real-time monitoring on the wind turbine to obtain monitoring information, wherein the monitoring information includes: the terminal voltage of the wind turbine and the rate of change of the terminal voltage of the wind turbine;

comparing the machine terminal voltage of the wind turbine with a preset voltage threshold, and comparing the change rate of the machine end voltage of the wind turbine with a preset change rate threshold to obtain comparison results respectively;

The converter and the low-voltage reactor of the wind turbine are controlled according to the comparison result, so as to complete the coordinated control of the high voltage ride-through of the wind turbine.
The method of claim 1, wherein the preset voltage threshold includes a first threshold, a second threshold and a third threshold, and the second threshold is greater than the first threshold and the third threshold .
The method according to claim 2, wherein the controlling the converter of the wind turbine according to the comparison result comprises:

In the case that the terminal voltage of the wind turbine is greater than or equal to the first threshold, start the first external controller;

When T is greater than or equal to the delay time of the reactive power control confirmation time of the converter of the wind turbine, control the first external controller to confirm the control command, and send the command to the converter of the wind turbine. A reactive power start control instruction, wherein the T is a time instruction signal for starting timing when the machine terminal voltage of the wind turbine reaches or exceeds the preset voltage threshold;

After the converter of the wind turbine is started according to the reactive power start control instruction, the converter of the wind turbine is controlled to absorb inductive reactive power in the grid.
The method according to claim 2, wherein the controlling the low-voltage reactor of the wind turbine according to the comparison result comprises:

In the case that the terminal voltage of the wind turbine is greater than or equal to the second threshold, start a second external controller;

When T is greater than or equal to the delay time of the low-voltage reactor switching-on confirmation time, control the second external controller to confirm the control command, turn on the thyristor bidirectional switch, switch on the low-voltage reactor, and control the The low-voltage reactor absorbs inductive reactive power in the grid;

Wherein, the second external controller is a controller based on thyristor switching, and the T is a time command signal for starting timing when the terminal voltage of the wind turbine reaches or exceeds the preset voltage threshold.
The method according to claim 2, wherein the controlling the low-voltage reactor of the wind turbine according to the comparison result comprises:

In the case that the terminal voltage of the wind turbine is less than the third threshold, and the rate of change of the terminal voltage of the wind turbine is less than the preset rate of change threshold, start the second external controller;

When T is greater than or equal to the delay time of the low-voltage reactor cut-off confirmation time, the second external controller is controlled to confirm the control command, cut off the thyristor bidirectional switch, and control the low-voltage reactor to exit operation, wherein, The T is a time command signal to start timing when the terminal voltage of the wind turbine reaches or exceeds the preset voltage threshold, and the second external controller is a controller based on thyristor switching.
A system for coordinating and controlling high voltage ride-through of wind turbines, comprising:

a monitoring module, configured to perform real-time monitoring on the wind turbine and obtain monitoring information, wherein the monitoring information includes: the terminal voltage of the wind turbine and the rate of change of the terminal voltage of the wind turbine;

The comparison module is configured to compare the machine terminal voltage of the wind turbine with a preset voltage threshold, and compare the change rate of the machine end voltage of the wind turbine with the preset change rate threshold, and obtain the comparison results respectively ;

The coordination control module is configured to control the converter and the low-voltage reactor of the wind turbine according to the comparison result, so as to complete the coordinated control of the high voltage ride through of the wind turbine.
The system according to claim 6, wherein the preset voltage threshold includes a first threshold, a second threshold and a third threshold, and the second threshold is greater than the first threshold and the third threshold .
The system according to claim 7, wherein the coordinated control module is configured to: start the first external controller when the terminal voltage of the wind turbine is greater than or equal to the first threshold;

When T is greater than or equal to the delay time of the reactive power control confirmation time of the converter of the wind turbine, control the first external controller to confirm the control command, and send it to the converter of the wind turbine A reactive power start control instruction, wherein the T is a time instruction signal for starting timing when the machine terminal voltage of the wind turbine reaches or exceeds the preset voltage threshold;

After the converter of the wind turbine is started according to the reactive power start control instruction, the converter of the wind turbine is controlled to absorb inductive reactive power in the grid.
The system of claim 7, wherein the coordinated control module is configured to:

In the case that the terminal voltage of the wind turbine is greater than or equal to the second threshold, start a second external controller;

When T is greater than or equal to the delay time of the low-voltage reactor switching-on confirmation time, control the second external controller to confirm the control command, turn on the thyristor bidirectional switch, switch on the low-voltage reactor, and control the The low-voltage reactor absorbs inductive reactive power in the grid;

Wherein, the second external controller is a controller based on thyristor switching, and the T is a time command signal for starting timing when the terminal voltage of the wind turbine reaches or exceeds the preset voltage threshold.
The system of claim 7, wherein the coordinated control module is configured to:

In the case that the terminal voltage of the wind turbine is less than the third threshold, and the rate of change of the terminal voltage of the wind turbine is less than the preset rate of change threshold, start the second external controller;

When T is greater than or equal to the delay time of the low-voltage reactor cut-off confirmation time, the second external controller is controlled to confirm the control command, cut off the thyristor bidirectional switch, and control the low-voltage reactor to exit operation, wherein, The T is a time command signal to start timing when the terminal voltage of the wind turbine reaches or exceeds the preset voltage threshold, and the second external controller is a controller based on thyristor switching.