CN111628684A - Optimal de-excitation control method and system for fault ride-through of doubly-fed fans - Google Patents

Abstract

The invention discloses an optimized de-excitation control method and system for fault ride-through of a doubly-fed fan, establishes a DFIG simplified transient component mathematical model; And the amplitudes of the two are in a predetermined proportional relationship; the amplitude and phase of the rotor transient current are controlled to limit the rotor overcurrent while taking into account the fastest transient process decay speed. At the same time, it reduces the transient power flowing into the DC bus through the RSC during the transient process, and suppresses the overvoltage of the DC bus. In summary, the optimized de-excitation control can accurately control the amplitude and phase of the rotor transient current, and take into account the fastest transient process decay speed while limiting the rotor overcurrent. At the same time, the optimized de-excitation control also effectively reduces the transient power flowing into the DC bus through the RSC during the transient process, and effectively suppresses the overvoltage of the DC bus.

Description

Optimal de-excitation control method and system for fault ride-through of doubly-fed fans

technical field

The invention belongs to the technical field of control, and in particular relates to an optimized de-excitation control method and system for fault ride-through of a double-fed fan.

Background technique

The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

With the rapid development of the wind power industry, the installed capacity of wind turbines is increasing, which has a greater impact on the operation of the power grid. Therefore, the safe operation of wind turbines has received more and more attention. Among the many fan types, the double-fed fan (DFIG) is widely used due to its small size and low cost.

The stator side of the DFIG is directly connected to the grid, and the disturbance of grid faults will have a huge impact on the DFIG. When the power grid fails, DFIG generates stator transient flux linkage and induces transient electromotive force in rotor windings, which may lead to overcurrent in rotor circuit and overvoltage of DC bus, threatening the safe operation of DFIG.

During the fault ride-through period, in order to ensure the safe operation of the DFIG, many hardware and software strategies have been proposed: one of the hardware strategies is to connect the crowbar circuit in the rotor winding, and put in the crowbar when the rotor winding current exceeds the specified value. circuit, which can effectively protect the rotor winding; the more widely used hardware strategy at present is to block the IGBT of the rotor side converter (RSC) after the rotor overcurrent, and perform uncontrolled rectification through the diode to avoid the IGBT being damaged by the overcurrent, while the transient The power flows into the DC bus through the diode uncontrolled rectification, causing the DC bus voltage to rise. At this time, the excess energy in the DC bus capacitor is consumed by the DC Chopper circuit to suppress the DC bus voltage rise. The investment of these hardware protection strategies will make the DFIG lose its controllability, and the additional hardware circuits will increase the cost, but they are indispensable protection methods in the face of serious grid failures.

In the face of minor grid faults or the follow-up problem of hardware protection strategy exit, de-excitation control is a popular software control strategy. This control strategy attempts to control the rotor transient current amplitude and the stator transient flux linkage amplitude to a certain value. proportional relationship, and at the same time make the rotor transient current and the stator transient flux out of phase to speed up the attenuation of the transient process. However, the actual effect of traditional demagnetization control is not ideal, and the amplitude and phase of the rotor transient current cannot be effectively controlled, and the expected target cannot be achieved.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides an optimized de-excitation control method for fault ride-through of a doubly-fed fan. Take into account the fastest transient process decay rate. At the same time, the optimized de-excitation control also effectively reduces the transient power flowing into the DC bus through the RSC during the transient process, and effectively suppresses the overvoltage of the DC bus.

To achieve the above object, one or more embodiments of the present invention provide the following technical solutions:

The optimal de-excitation control method for fault ride-through of DFIG includes:

Establish DFIG simplified transient component mathematical model;

Based on the above model, the rotor transient current obtained by the de-excitation control is made to be out of phase with the stator transient flux linkage, and the amplitudes of the two are in accordance with a predetermined proportional relationship;

Control the amplitude and phase of the rotor transient current, limit the rotor overcurrent while taking into account the fastest transient process decay speed, at the same time, reduce the transient power influx into the DC bus through the RSC during the transient process, and suppress the DC bus overcurrent. Voltage.

A further technical solution, when DFIG simplifies the establishment of the transient component mathematical model:

A third-order complex state space equation model is established for DFIG, and it is decomposed into a state equation (GPT) describing the adjustment process of the power frequency component and a state equation (ZTS) describing the transient attenuation component caused by the voltage disturbance after the grid voltage disturbance;

Considering only the main transient component (MTC), the third-order equation of state is reduced to a first-order equation of state and the main transient component is solved.

In a further technical solution, in the DFIG simplified transient component model, based on the attenuation change law of the stator transient flux linkage, the differential equation of the stator transient flux linkage is obtained, and based on the differential equation, the rotor transient current amplitude and the stator transient flux are controlled. The magnitude of the flux linkage is proportional to a certain ratio, and the transient current of the rotor and the transient flux of the stator are reversed to speed up the attenuation of the transient process.

A further technical solution is to convert the proportional coefficient of the de-excitation control from a real number to a complex number K _{mag_real} + _{jK mag_imag} , so that the multiple relationship between the rotor transient current and the stator transient flux linkage is a negative real number, and the absolute value of the negative real number is equal to the expectation The demagnetization control gain.

In a further technical solution, the real part and imaginary part of the demagnetization control coefficient should satisfy the following two formulas:

According to the formula, the real and imaginary parts of the demagnetization control coefficient are obtained.

An optimized de-excitation control system for fault ride-through of a doubly-fed fan includes a controller configured to:

Establish DFIG simplified transient component mathematical model;

Based on the above model, the rotor transient current obtained by the de-excitation control is inverse to the stator transient flux linkage and its amplitude conforms to a predetermined proportional relationship with the stator transient flux linkage;

The amplitude and phase of the rotor transient current are controlled to limit the rotor overcurrent while taking into account the fastest transient process decay speed. At the same time, it reduces the transient power flowing into the DC bus through the RSC during the transient process, and suppresses the overvoltage of the DC bus.

One or more of the above technical solutions have the following beneficial effects:

Based on the simplified transient component model of DFIG, this paper improves the traditional de-excitation control and proposes an optimized de-excitation control strategy. The optimized de-excitation control can accurately control the amplitude and phase of the rotor transient current, while limiting the rotor over-current while taking into account the fastest decay speed in the transient process. The transient power flowing into the DC bus through the RSC effectively suppresses the overvoltage of the DC bus.

Based on the attenuation characteristics of the stator transient flux linkage, the invention establishes a DFIG simplified transient component mathematical model, improves the traditional demagnetization control, and proposes an optimized demagnetization control strategy, which can accurately control the rotor transient The amplitude and phase of the state current are limited, and the fastest transient process decay speed is taken into account while limiting the rotor overcurrent. At the same time, the optimized de-excitation control also effectively reduces the transient power flowing into the DC bus through the RSC during the transient process, and effectively suppresses the overvoltage of the DC bus. A grid-connected DFIG model with optimized de-excitation control technology is built in PowerFactory software, and the simulation results verify the effectiveness of the optimal de-excitation control strategy.

Description of drawings

The accompanying drawings forming a part of the present invention are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation of the present invention.

Figure 1 is a block diagram of traditional de-excitation control;

2 is a block diagram of an improved de-excitation control according to an embodiment of the present invention;

FIG. 3 is a comparison diagram of the rotor current amplitude of the demagnetization control according to the embodiment of the present invention;

Fig. 4 is the amplitude diagram of the transient current of the rotor and the transient flux linkage of the stator under the traditional de-excitation control;

Fig. 5 is the amplitude diagram of rotor transient current and stator transient flux linkage in improved de-excitation control according to an embodiment of the present invention;

Figure 6 is a diagram of the transient current of the dq-axis rotor and the transient flux linkage of the stator under traditional de-excitation control;

Figure 7 shows the dq-axis rotor transient current and stator transient flux linkage under improved de-excitation control;

FIG. 8 is a comparison diagram of the DC bus voltage of the de-excitation control.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

Embodiments of the invention and features of the embodiments may be combined with each other without conflict.

Example 1

As introduced in the Background Art: During the fault ride-through period of a doubly-fed wind turbine (DFIG), transient currents will be generated in the stator and rotor under the influence of grid voltage disturbance, which is likely to cause overcurrent of the rotor-side converter (RSC). and overvoltage of the DC bus. De-excitation control is a method of controlling the transient current of the rotor, trying to control the amplitude of the transient current of the rotor to be proportional to the amplitude of the transient flux of the stator. At the same time, the rotor transient current and the stator transient flux linkage are made out of phase to speed up the attenuation of the transient process. However, the effect of traditional demagnetization control is not ideal, and the amplitude and phase of the rotor transient current cannot be effectively controlled, and the expected target cannot be achieved.

Therefore, this embodiment discloses an optimized de-excitation control method for fault ride-through of a doubly-fed fan, establishes a DFIG simplified transient component mathematical model, improves the traditional de-excitation control, and proposes an optimized de-excitation control strategy. The control can accurately control the amplitude and phase of the rotor transient current, and take into account the fastest transient process decay speed while limiting the rotor overcurrent. The transient power entering the DC bus effectively suppresses the overvoltage of the DC bus.

Firstly, the simplified transient component mathematical model of DFIG is introduced, and a third-order complex state space equation model is established for DFIG. After grid voltage disturbance, it is decomposed into state equation (GPT) describing the adjustment process of power frequency Equation of State (ZTS) for the state decay component. The transient process in GPT has a very short duration, while the transient process in ZTS has a long duration and large amplitude, and is the main component of the transient process after a fault. Among them, there are three frequency attenuation components in the solution of the state variable of ZTS, one of which is attenuated slower than the other two frequency components and has a larger initial value, and the grid frequency with a frequency close to negative can approximately represent the complete solution, which is named is the main transient component (MTC). In order to simplify the calculation, only the MTC component is considered, thus reducing the order of the third-order state equation of ZTS, and a method for solving the natural transient voltage and current of RSC which only considers the MTC component is proposed. The first-order state equation is reduced to a first-order state equation and the MTC component is solved. The main formula is as follows:

in:

为转子暂态电流，

为定子暂态磁链，

为RSC输出暂态电压。L_s*、L_r*、L_m*、R_s*、R_r*均为DFIG参数，ω_r*为转子转速，ω_1*为电网频率，可作为常数100π，即等于ω_B。K_mod是电流环输出信号经由调制形成RSC输出电压的等效比例系数，是一个常数。K_p，K_i是电流环PI调节器的比例增益和积分增益。The subscript * represents the per-unit value,

is the rotor transient current,

is the stator transient flux linkage,

Transient voltage output for RSC. L _s* , L _r* , L _m* , R _s* , R _r* are all DFIG parameters, ω _r* is the rotor speed, and ω _1* is the grid frequency, which can be used as a constant 100π, which is equal to ω _B . K _mod is the equivalent proportional coefficient of the output voltage of the RSC formed by the current loop output signal through modulation, and is a constant. K _p , K _i are the proportional gain and integral gain of the current loop PI regulator.

Attenuation characteristics of stator transient flux linkage: In the DFIG simplified transient component model, the attenuation variation law of stator transient flux linkage can be expressed by the following formula:

是定子绕组暂态电流，根据定子磁链方程，可得定子暂态电流如下：In the above formula,

is the stator winding transient current. According to the stator flux linkage equation, the stator transient current can be obtained as follows:

The differential equation of the stator transient flux linkage can be obtained as follows:

It can be seen from equation (5) that at a certain moment, under the same rotor transient current amplitude, if the phase of the rotor transient current is opposite to the phase of the stator transient flux linkage, then this phase relationship will make the stator transient at this moment. The state flux decays faster than all other phase relationships. In view of this, the demagnetization control attempts to control the rotor transient current amplitude to be proportional to the stator transient flux linkage amplitude, and at the same time make the rotor transient current and the stator transient flux linkage out of phase to speed up the attenuation of the transient process.

Analysis of traditional de-excitation control, as shown in Figure 1, the traditional de-excitation control of DFIG intends to control the rotor transient current and stator transient current by inputting a rotor transient current signal opposite to the stator transient flux linkage into the current control command. The flux linkage presents a specific ratio, and the two phases are reversed to accelerate the decay of the transient process.

However, the current command is an AC quantity close to the grid frequency in the dq coordinate system. The rotor current control using the PI regulator cannot accurately make the realized rotor transient current equal to the command value, and cannot make the realized rotor transient current equal to the command value. The stator flux linkage is reversed, and the amplitude of the rotor transient current is not equal to the expectation, so the expected de-excitation control effect cannot be achieved, and the rotor transient current cannot be effectively controlled, resulting in the inability to achieve the de-excitation control effect. expected.

Extending the derived simplified transient component model to DFIG under traditional de-excitation control, the approximate relationship between rotor transient current and stator transient flux linkage under traditional de-excitation control can be obtained as follows:

与

并不能完全反相，并且

的幅值也不等于

的幅值。Among them, K _mag is the proportional coefficient of demagnetization control. According to formula (6), it can be seen that under the traditional demagnetization control, the

and

is not completely inverting, and

The magnitude of is not equal to

the magnitude of .

Optimizing the de-excitation control strategy: if K _mag is converted from a real number to a complex number K _{mag_real} + _{jK mag_imag} , the coefficient on the right side of equation (6) is a negative real number as a whole, and the absolute value of the negative real number is equal to the desired de-excitation control gain ( G _mag ), that is, it is hoped that the rotor transient current and the stator transient flux linkage are proportional, so that the rotor transient current obtained by the de-excitation control and the stator transient flux linkage can be out of phase and the amplitude is in line with the predetermined value and the stator transient flux linkage. The proportional relationship of the transient flux linkage. For this purpose, the real and imaginary parts of the demagnetization control coefficient should satisfy the following two equations:

Solutions have to:

According to the above derivation, the flow chart of optimizing the demagnetization control strategy can be shown in Figure 2, and the specific flow can be expressed as follows:

(1) Under the condition that the capacity of the rotor-side converter allows, determine the demagnetization gain G _mag of the optimal demagnetization control.

(2) Calculate the real part and imaginary part of the de-excitation control proportional coefficient according to the formula (8), and calculate the transient current command value at this time.

(3) By superimposing the command value in (2) and the positive sequence current command value, the total current command value can be obtained, and input it to the PI controller to realize the optimal de-excitation control.

Simulation verification: In order to test the performance of the optimal de-excitation control strategy for the fault ride-through of the DFIG proposed in this paper, a 2MW grid-connected DFIG stand-alone model is built in the DIgSILENT/Power Factory software, and some parameters are shown in Table 1.

Table 1 DFIG part parameters

作为灭磁控制暂态转子电流指令。在0.3p.u电压阶跃跌落扰动下，无灭磁控制、传统灭磁控制以及改进灭磁控制下的转子电流幅值如图3所示。It is determined that the de-excitation gain G _mag =3, that is, it is expected that the amplitude of the transient current of the control rotor is three times the amplitude of the transient flux linkage of the stator and is out of phase with the transient flux linkage of the stator. The improved demagnetization control is calculated based on the complex coefficient of K _{mag_real} + _{jK mag_imag} to generate the transient rotor current command for demagnetization control, while the traditional demagnetization control directly uses -3

It is used as the transient rotor current command for de-excitation control. Under the disturbance of 0.3pu voltage step drop, the rotor current amplitudes under no demagnetization control, traditional demagnetization control and improved demagnetization control are shown in Figure 3.

Figures 4 and 5 show the amplitudes of the rotor transient current and the stator transient flux linkage under the traditional de-excitation control and the improved de-excitation control.

As can be seen from the above two figures, the rotor transient current amplitude under the traditional de-excitation control has exceeded 3 times the stator transient flux linkage amplitude, and the predetermined rotor transient current amplitude target has not been achieved, which is also the cause of the rotor Causes of transient overcurrents. The rotor transient current amplitude under the improved de-excitation control can accurately meet the goal of three times the stator transient flux linkage amplitude.

In addition, in the control of the rotor transient current phase, the comparison between the traditional de-excitation control and the improved de-excitation control is shown in Figures 6 and 7.

It can be seen that the traditional de-excitation control does not realize the inversion of the rotor transient current and the stator transient flux linkage, and cannot achieve the fastest decay under the current amplitude of the rotor current. The phase correction of the state flux linkage is reversed, and the purpose of the fastest decay is achieved under the accurate control of the transient current amplitude.

In addition, the improved demagnetization control also reduces the transient active power entering the DC bus through the rotor-side converter during the entire transient process, and suppresses the increase of the DC bus voltage.

According to the simplified transient component model of DFIG, the traditional de-excitation control is improved, and an optimized de-excitation control is proposed. The optimized de-excitation control can precisely control the amplitude and phase of the transient rotor current, so that the rotor transient current amplitude and the stator transient flux linkage amplitude have a specific proportional relationship, and at the same time, the rotor transient current phase is proportional to the stator transient flux. The flux linkage is accurately reversed, and the transient current amplitude is controlled to avoid overcurrent and at the same time accelerate the decay speed of the transient process. In addition, the optimized de-excitation control can effectively reduce the problem of DC overvoltage during the fault transient process. To sum up, the optimized de-excitation control can significantly improve the fault ride-through operation of DFIG.

Embodiment 2

The purpose of this embodiment is to provide a computing device, comprising a memory, a processor and a computer program stored in the memory and running on the processor, the processor implements the following steps when executing the program, including:

Establish DFIG simplified transient component mathematical model;

Based on the above model, the rotor transient current obtained by the de-excitation control is inverse to the stator transient flux linkage, and its amplitude conforms to a predetermined proportional relationship with the stator transient flux linkage;

Control the amplitude and phase of the rotor transient current, limit the rotor overcurrent while taking into account the fastest transient process decay speed, at the same time, reduce the transient power influx into the DC bus through the RSC during the transient process, and suppress the DC bus overcurrent. Voltage.

Embodiment 3

The purpose of this embodiment is to provide a computer-readable storage medium.

A computer-readable storage medium on which a computer program is stored, the program executes the following steps when executed by a processor:

Establish DFIG simplified transient component mathematical model;

Based on the above model, the rotor transient current obtained by the de-excitation control is inverse to the stator transient flux linkage, and its amplitude conforms to a predetermined proportional relationship with the stator transient flux linkage;

The amplitude and phase of the rotor transient current are controlled to limit the rotor overcurrent while taking into account the fastest transient process decay speed. At the same time, it reduces the transient power flowing into the DC bus through the RSC during the transient process, and suppresses the overvoltage of the DC bus.

The steps involved in the apparatuses in the second and third embodiments above correspond to the method embodiment 1, and the specific implementation can refer to the relevant description part of the embodiment 1. The term "computer-readable storage medium" should be understood to include a single medium or multiple media including one or more sets of instructions; it should also be understood to include any medium capable of storing, encoding or carrying for use by a processor The executed instruction set causes the processor to perform any of the methods of the present invention.

Those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by the computing device, so that they can be stored in a storage device. The device is executed by a computing device, or they are separately fabricated into individual integrated circuit modules, or multiple modules or steps in them are fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, they do not limit the scope of protection of the present invention. Those skilled in the art should understand that on the basis of the technical solutions of the present invention, those skilled in the art do not need to pay creative work. Various modifications or deformations that can be made are still within the protection scope of the present invention.

Claims (10)

1. The optimized de-excitation control method for doubly-fed fan fault ride-through is characterized by comprising the following steps:

establishing a DFIG simplified transient component mathematical model of the doubly-fed wind turbine;

enabling the rotor transient current obtained by de-excitation control to be opposite to the stator transient flux linkage based on the model, and enabling the amplitude of the rotor transient current to accord with a preset proportional relation with the stator transient flux linkage;

the amplitude and the phase of the transient current of the rotor are controlled, the fastest transient process attenuation speed is considered while the rotor overcurrent is limited, meanwhile, the transient power which is rushed into a direct current bus through a rotor side converter RSC in the transient process is reduced, and the direct current bus overvoltage is restrained.

2. The method for controlling the optimized de-excitation of the fault ride-through of the doubly-fed wind turbine as claimed in claim 1, wherein when a DFIG simplified transient component mathematical model of the doubly-fed wind turbine is established:

a three-order complex state space equation model is established for the DFIG, and the model is decomposed into a state equation GPT describing a power frequency component adjusting process and a state equation ZTS describing a transient attenuation component caused by voltage disturbance after the voltage of a power grid is disturbed.

3. The method for controlling the optimal de-excitation of the fault ride-through of the doubly-fed wind turbine as claimed in claim 2, wherein attenuation components of three frequencies exist in the solution of the state variable of ZTS, one frequency component is slower in attenuation and larger in initial value than the other two frequency components, and the grid frequency with the frequency close to negative can approximately represent a complete solution, and is named as a main transient component MTC.

4. The method for controlling the optimal de-excitation of the doubly-fed wind turbine fault ride-through of claim 3, wherein only MTC components are considered, a three-order state equation is reduced to a one-order state equation, and the MTC components are solved.

5. The method for controlling the optimal de-excitation of the fault ride-through of the doubly-fed wind turbine as claimed in claim 1, wherein in the DFIG simplified transient component model, a differential equation of the stator transient flux linkage is obtained based on an attenuation change rule of the stator transient flux linkage. Based on a differential equation, the transient current amplitude of the rotor and the transient flux linkage amplitude of the stator are controlled to be in a certain proportional relation, and meanwhile, the transient current of the rotor and the transient flux linkage of the stator are reversed to accelerate the attenuation of a transient process.

6. The method for optimized de-excitation control of doubly-fed wind turbine fault ride-through of claim 1, wherein the proportionality coefficient of de-excitation control is converted from real number to complex number K_{mag_real}+jK_{mag_imag}And the rotor transient current and the stator transient flux linkage are in a negative real number relation, and the absolute value of the negative real number is equal to the expected demagnetization control gain.

7. The method for controlling the optimal de-excitation of the fault ride-through of the doubly-fed wind turbine as claimed in claim 6, wherein the real part and the imaginary part of the de-excitation control coefficient should satisfy the following two equations:

and obtaining the real part and the imaginary part of the demagnetization control coefficient according to the formula.

8. The optimized de-excitation control system for doubly-fed wind turbine fault ride-through comprises a controller, and is characterized in that the controller is configured to:

establishing a DFIG simplified transient component mathematical model;

enabling the rotor transient current obtained by de-excitation control to be opposite to the stator transient flux linkage based on the model, and enabling the amplitude of the rotor transient current to accord with a preset proportional relation with the stator transient flux linkage;

the amplitude and the phase of the rotor transient current are controlled, and the fastest transient process attenuation speed is considered while the rotor overcurrent is limited. Meanwhile, transient power which is rushed into the direct current bus through the RSC in the transient process is reduced, and overvoltage of the direct current bus is restrained.

9. A computing device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein the processor executes the program to perform steps comprising:

establishing a DFIG simplified transient component mathematical model;

enabling the rotor transient current obtained by de-excitation control to be opposite to the stator transient flux linkage based on the model, and enabling the amplitude of the rotor transient current to accord with a preset proportional relation with the stator transient flux linkage;

the amplitude and the phase of the rotor transient current are controlled, and the fastest transient process attenuation speed is considered while the rotor overcurrent is limited. Meanwhile, transient power which is rushed into the direct current bus through the RSC in the transient process is reduced, and overvoltage of the direct current bus is restrained.

10. A computer-readable storage medium, having a computer program stored thereon, the program, when executed by a processor, performing the steps of:

establishing a DFIG simplified transient component mathematical model;

enabling the rotor transient current obtained by de-excitation control to be opposite to the stator transient flux linkage based on the model, and enabling the amplitude of the rotor transient current to accord with a preset proportional relation with the stator transient flux linkage;

the amplitude and the phase of the rotor transient current are controlled, and the fastest transient process attenuation speed is considered while the rotor overcurrent is limited. Meanwhile, transient power which is rushed into the direct current bus through the RSC in the transient process is reduced, and overvoltage of the direct current bus is restrained.

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