A Fault Ride-Through Control Method and System for Offshore Doubly Fed Wind Turbines

Abstract

The present invention provides a fault ride-through control method and system for an offshore doubly-fed wind turbine generator set, including: when a fault occurs, determining whether the terminal voltage of the offshore doubly-fed wind turbine generator set exceeds the limit according to the collected terminal voltage; if so, the offshore wind power grid-connected system enters the low-voltage duration period and executes the pre-set active and reactive power coordinated control; otherwise, when the time for the terminal voltage to return to normal is within the time threshold, the offshore wind power grid-connected system enters the post-fault clearing stage and executes the reactive power support withdrawal control. This method and system consider the transient characteristic changes caused by the high-voltage AC transmission AC cable of the offshore wind power, execute the active and reactive power coordinated control during the low-voltage period, and execute the reactive power support withdrawal control after the fault is cleared, improving the fault ride-through ability of the offshore wind power grid-connected system and enhancing the stability of the offshore wind power grid-connected system.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy power generation control, and particularly relates to a fault ride-through control method and system for an offshore doubly-fed wind turbine generator set. Background Art

[0002] There are mainly three grid-connected power transmission methods for offshore wind farms: high-voltage alternating current (AC) power transmission technology, high-voltage direct current (DC) power transmission technology, and frequency-divided power transmission technology. Since high-voltage AC power transmission technology has significant advantages in short-distance transmission, it has become the commonly used power transmission method for offshore wind farms. Offshore wind power high-voltage AC transmission lines generally use submarine AC cables. Compared with the overhead lines commonly used in onshore wind power, submarine AC cables have a relatively large capacitive charging reactive power, and their voltage characteristics and transient characteristics are significantly different, making it easy to occur overvoltage problems. In response to the technical challenges faced by the offshore wind power grid-connected system, a large amount of research work has been carried out by the academic circles at home and abroad. Great progress has been made mainly in aspects such as power transmission, substation design, and operation control of offshore wind power, focusing on content such as high-voltage AC / DC power transmission technology for offshore wind power, optimized design of substation systems, power prediction, and remote cluster control. However, after a fault occurs, the transient characteristics of the offshore wind farm power transmission system through the AC cable change, and the traditional fault ride-through control methods of wind turbine generator sets face adaptability problems, and the fault ride-through of the offshore wind power system through the AC cable will face new difficulties. Summary of the Invention

[0003] To overcome the deficiencies of the above-mentioned existing technologies that are difficult to adapt to the fault ride-through of offshore wind power, the present invention proposes a fault ride-through control method for an offshore doubly-fed wind turbine generator set. The improvement lies in that it includes:

[0004] When a fault occurs, according to the terminal voltage of the offshore doubly-fed wind turbine generator set collected, determine whether the terminal voltage exceeds the limit:

[0005] If so, the offshore wind power grid-connected system enters the low-voltage duration period, and perform the pre-set active and reactive power coordinated control;

[0006] Otherwise, when the time for the terminal voltage to return to normal is within the time threshold, the offshore wind power grid-connected system enters the post-fault clearance stage, and perform the reactive power support withdrawal control.

[0007] The first preferred technical solution provided by the present invention, the improvement lies in that the determining whether the terminal voltage exceeds the limit according to the terminal voltage of the offshore doubly-fed wind turbine generator set collected includes:

[0008] Judge whether the terminal voltage of the offshore doubly-fed wind turbine generator set collected is less than or equal to the voltage threshold:

[0009] If so, the terminal voltage exceeds the limit, otherwise the terminal voltage does not exceed the limit.

[0010] The second preferred technical solution provided by the present invention is improved in that the execution of the pre-set active and reactive power coordinated control includes:

[0011] Calculating the injected active current and the injected reactive current during the low-voltage duration of the doubly-fed wind turbine according to the terminal voltage;

[0012] Based on the injected active current and the injected reactive current during the low-voltage duration, performing active and reactive power coordinated control.

[0013] The third preferred technical solution provided by the present invention is improved in that the calculation formula of the injected reactive current during the low-voltage duration is as follows:

[0014] I q1 = 1.5(U e - U T )I N

[0015] The calculation formula of the injected active current during the low-voltage duration is as follows:

[0016]

[0017] Wherein, I q1 represents the injected reactive current during the low-voltage duration, U e represents the voltage threshold, U T represents the terminal voltage, I N represents the rated current, I p1 represents the injected active current during the low-voltage duration, I max represents the maximum voltage.

[0018] The fourth preferred technical solution provided by the present invention is improved in that the execution of the reactive power support withdrawal control includes:

[0019] Calculating the injected active current and the injected reactive current during the reactive power support withdrawal period of the doubly-fed wind turbine according to the terminal voltage;

[0020] Based on the injected active current and the injected reactive current during the reactive power support withdrawal period, performing active and reactive power coordinated control.

[0021] The fifth preferred technical solution provided by the present invention is improved in that the calculation formula of the injected active current during the reactive power support withdrawal period is as follows:

[0022]

[0023] The calculation formula of the injected reactive current during the reactive power support withdrawal period is as follows:

[0024]

[0025] Among them, I p2 represents the injected active current during the withdrawal of reactive power support, and L s represents the stator inductance of the doubly-fed wind turbine generator set, and L m represents the mutual inductance between the stator and rotor of the doubly-fed wind turbine generator set, and U T represents the terminal voltage, and P ref represents the steady-state value of the active power; I q2 represents the injected reactive current during the withdrawal of reactive power support.

[0026] The sixth preferred technical solution provided by the present invention is improved in that before a fault occurs:

[0027] Design the coordinated control of active and reactive power during the low-voltage duration of the offshore doubly-fed wind turbine generator set based on the terminal voltage and the reactive power support withdrawal control after fault clearing;

[0028] And determine that the coordinated control of active and reactive power during the low-voltage duration of the offshore doubly-fed wind turbine generator set based on the terminal voltage and the reactive power support withdrawal control after fault clearing operate normally in the control system of the offshore doubly-fed wind turbine generator set.

[0029] An offshore doubly-fed wind turbine generator set fault ride-through control system is improved in that it includes: a judgment module, a coordinated control module, and a reactive power withdrawal module;

[0030] The judgment module is used to determine whether the terminal voltage exceeds the limit according to the collected terminal voltage of the offshore doubly-fed wind turbine generator set when a fault occurs;

[0031] The coordinated control module is used to execute the pre-set coordinated control of active and reactive power when the terminal voltage exceeds the limit and the offshore wind power grid-connected system enters the low-voltage duration;

[0032] The reactive power withdrawal module is used to execute the reactive power support withdrawal control when the terminal voltage does not exceed the limit and the time for the terminal voltage to return to normal is within the time threshold and the offshore wind power grid-connected system enters the post-fault clearing stage.

[0033] The seventh preferred technical solution provided by the present invention is improved in that the coordinated control module includes: a coordinated control calculation unit and a coordinated control unit;

[0034] The coordinated control calculation unit is used to calculate the injected active current and the injected reactive current during the low-voltage duration of the doubly-fed wind turbine generator set according to the terminal voltage;

[0035] The coordinated control unit performs coordinated control of active and reactive power based on the injected active current and the injected reactive current during the low-voltage duration.

[0036] The eighth preferred technical solution provided by the present invention is improved in that the reactive power withdrawal module includes: a reactive power withdrawal calculation unit and a reactive power withdrawal control unit;

[0037] The reactive power withdrawal calculation unit is used to calculate the injected active current and the injected reactive current during the reactive power support withdrawal period of the doubly-fed wind turbine according to the terminal voltage;

[0038] The reactive power withdrawal control unit is used to perform active and reactive power coordinated control based on the injected active current and the injected reactive current during the reactive power support withdrawal period.

[0039] Compared with the closest prior art, the present invention has the following beneficial effects:

[0040] The present invention provides a fault ride-through control method and system for an offshore doubly-fed wind turbine. When a fault occurs, it determines whether the terminal voltage of the offshore doubly-fed wind turbine exceeds the limit according to the collected terminal voltage: if so, the offshore wind power grid-connected system enters the low-voltage duration period and performs the preset active and reactive power coordinated control; otherwise, when the time for the terminal voltage to return to normal is within the time threshold, the offshore wind power grid-connected system enters the post-fault clearance stage and performs reactive power support withdrawal control. The present invention takes into account the transient characteristic changes caused by the high-voltage AC transmission AC cable of the offshore wind power, performs active and reactive power coordinated control during the low-voltage period, and performs reactive power support withdrawal control after the fault is cleared, improving the fault ride-through ability of the offshore wind power grid-connected system and enhancing the stability of the offshore wind power grid-connected system. Description of the Drawings

[0041] Figure 1 It is a schematic flow chart of a fault ride-through control method for an offshore doubly-fed wind turbine provided by the present invention;

[0042] Figure 2 It is a schematic flow chart of an embodiment of a fault ride-through control method for an offshore doubly-fed wind turbine provided by the present invention;

[0043] Figure 3 It is a schematic diagram of the control structure and principle of a fault ride-through control method for an offshore doubly-fed wind turbine provided by the present invention;

[0044] Figure 4 It is a schematic diagram of the basic structure of a fault ride-through control system for an offshore doubly-fed wind turbine provided by the present invention;

[0045] Figure 5 It is a schematic diagram of the detailed structure of a fault ride-through control system for an offshore doubly-fed wind turbine provided by the present invention. Detailed Description of the Invention

[0046] The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0047] High-voltage AC power transmission technology is generally adopted for offshore wind power transmission. The use of submarine AC cables makes the capacitive charging reactive power of the transmission line increase, and the transient characteristics of the offshore wind power grid-connected system change significantly after a short-circuit fault, affecting the fault ride-through characteristics of the system. In view of the problem of difficult fault ride-through caused by the increased capacitance of the transmission line in the offshore wind power grid-connected system, the present invention proposes a fault ride-through control method and system for offshore doubly-fed wind turbine generators to improve the fault ride-through ability of the offshore wind power grid-connected system.

[0048] A schematic flow chart of a fault ride-through control method for an offshore doubly-fed wind turbine generator provided by the present invention is as Figure 1 shown and includes:

[0049] Step 1: When a fault occurs, determine whether the terminal voltage of the offshore doubly-fed wind turbine generator exceeds the limit according to the collected terminal voltage of the offshore doubly-fed wind turbine generator:

[0050] Step 2: If so, the offshore wind power grid-connected system enters the low-voltage duration period, and perform the pre-set active and reactive power coordinated control;

[0051] Step 3: Otherwise, when the time for the terminal voltage to return to normal is within the time threshold, the offshore wind power grid-connected system enters the post-fault clearance stage and perform the reactive power support withdrawal control.

[0052] Specifically, the implementation process of the fault ride-through control method for the offshore doubly-fed wind turbine generator is as follows:

[0053] Step 101: Design a fault ride-through control strategy for the offshore doubly-fed wind turbine generator based on the terminal voltage.

[0054] The fault ride-through control strategy for the offshore doubly-fed wind turbine generator includes: determining the control mode to be adopted according to the terminal voltage of the offshore doubly-fed wind turbine generator, and the control mode includes a fault ride-through control mode or a steady-state operation control mode. Specifically, the fault ride-through control mode determines the active current and reactive current output by the offshore doubly-fed wind turbine generator according to the terminal voltage, and performs active and reactive coordinated control and reactive power support withdrawal control, that is, the fault ride-through control mode includes the active and reactive power coordinated control during the low-voltage duration period and the reactive power support withdrawal control during the post-fault clearance stage. Its specific process is as Figure 2 , and the control structure and principle are as Figure 3 , including two-stage control functions.

[0055] 1) Active and reactive coordinated control of the doubly-fed wind turbine generator during the low-voltage duration period.

[0056] Among them, the reactive current is injected according to the minimum dynamic reactive requirement of the low-voltage ride-through technology requirements for wind farms in GB / T 19963—2011. Under the condition of meeting the dynamic reactive current injection condition, the remaining capacity of the wind turbine generates active power. The active and reactive coordinated control strategies of the doubly-fed wind turbine during the low-voltage duration are as follows.

[0057] I q1 =1.5(U e -U T )I N

[0058]

[0059] In the formula, where I q1 represents the injected reactive current during the low-voltage duration, T represents the terminal voltage, I N represents the rated current, I p1 represents the injected active current during the low-voltage duration, I max represents the maximum voltage, U e represents the voltage threshold. When the terminal voltage is less than or equal to the voltage threshold, it enters the low-voltage duration state. U e The specific value can be taken as 0.9. Usually, the terminal voltage is greater than or equal to 0.2. Therefore, the value range of U T in the above formula is [0.2, 0.9].

[0060] 2) Reactive support withdrawal control after fault clearance.

[0061] After fault clearance, the reactive support withdraws as soon as possible and absorbs reactive power as needed, and the active power resumes to the normal level value as soon as possible. The active and reactive coordinated control strategies of the doubly-fed wind turbine after fault clearance are as follows.

[0062]

[0063]

[0064] In the formula, I p2 represents the injected active current during the reactive support withdrawal period, L s represents the stator inductance of the doubly-fed wind turbine, L m represents the mutual inductance between the stator and rotor of the doubly-fed wind turbine, U T represents the terminal voltage, P ref represents the steady-state value of the active power; I q2 represents the injected reactive current during the reactive support withdrawal period.

[0065] Step 102: Determine that the fault ride-through control strategy based on the terminal voltage of the offshore doubly-fed wind turbine operates normally in the offshore doubly-fed wind turbine control system.

[0066] The doubly-fed wind turbine operates according to the pre-designed active and reactive power coordinated fault ride-through control strategy to ensure that the doubly-fed wind turbine can operate in two different control modes respectively: steady-state operation control mode and fault ride-through control mode.

[0067] Step 103: Based on the detected terminal voltage signal, determine whether the offshore wind power grid-connected system is in a short-circuit fault state and determine the control mode.

[0068] Step 103 specifically includes: Detect the terminal voltage U of the offshore doubly-fed wind turbine in real time T , and determine whether the terminal voltage exceeds the limit:

[0069] If the terminal voltage is less than or equal to the preset voltage threshold, the offshore wind power grid-connected system enters the first stage of fault ride-through in the preset fault ride-through control mode;

[0070] When the terminal voltage is greater than the preset voltage threshold and the duration of the voltage being greater than the preset voltage threshold is less than the preset time threshold, the offshore wind power grid-connected system enters the second stage of fault ride-through in the preset fault ride-through control mode;

[0071] Otherwise, the offshore wind power grid-connected system enters the preset steady-state operation control mode.

[0072] In actual operation, the voltage threshold can be set to 0.9 pu, and the time threshold can be set to 10 seconds.

[0073] Step 104: When the terminal voltage exceeds the limit, the fault ride-through control mode of the offshore doubly-fed wind turbine is activated.

[0074] In the active and reactive power coordinated fault ride-through control strategy of the offshore doubly-fed wind turbine, the active and reactive power coordinated control during the low-voltage duration and the active and reactive power coordinated control of the doubly-fed wind turbine after fault clearing are activated. This control method includes two different control processes. When the terminal voltage is less than or equal to 0.9 pu, it is the low-voltage duration, that is, the first stage of fault ride-through. The active and reactive power coordinated control during the low-voltage duration is executed. Among them, the reactive current is injected according to the minimum dynamic reactive power requirement of the low-voltage ride-through technical requirements for wind farms in GB / T 19963-2011. Under the condition of meeting the dynamic reactive current injection condition, the remaining capacity of the wind turbine generates active power; within 10 s after the terminal voltage recovers above 0.9 pu, it is the process after fault clearing, that is, the second stage of fault ride-through. The active and reactive power coordinated control after fault clearing is executed. Among them, the reactive support exits as soon as possible and absorbs reactive power according to needs, and at the same time, the active power resumes to the normal level value as soon as possible.

[0075] Step 105: When the terminal voltage is normal, the steady-state operation control mode of the offshore doubly-fed wind turbine is activated.

[0076] In the active and reactive power coordinated fault ride-through control strategy of the offshore doubly-fed wind turbine, during the low voltage duration, the active and reactive power coordinated control of the doubly-fed wind turbine and the active and reactive power coordinated control function after fault clearing do not work, and the doubly-fed wind turbine is in the steady-state operation control state.

[0077] In the present invention, different unit fault ride-through control strategies are adopted respectively during low voltage period and after fault clearing, which improves the fault ride-through ability of the offshore wind power grid-connected system and enhances the stability of the offshore wind power grid-connected system.

[0078] Embodiment 2:

[0079] Based on the same inventive concept, the present invention also provides an offshore doubly-fed wind turbine fault ride-through control system. Since the principles of these devices for solving technical problems are similar to those of the offshore doubly-fed wind turbine fault ride-through control method, the repeated parts will not be described in detail.

[0080] The basic structure of the system is as Figure 4 shown, and it includes: a judgment module, a coordinated control module and a reactive power withdrawal module;

[0081] Among them, the judgment module is used to determine whether the terminal voltage of the offshore doubly-fed wind turbine exceeds the limit according to the collected terminal voltage of the offshore doubly-fed wind turbine when a fault occurs;

[0082] The coordinated control module is used to execute the pre-set active and reactive power coordinated control when the offshore wind power grid-connected system enters the low voltage duration with the terminal voltage exceeding the limit;

[0083] The reactive power withdrawal module is used to execute the reactive power support withdrawal control when the offshore wind power grid-connected system enters the post-fault clearing stage with the terminal voltage not exceeding the limit and the time for the terminal voltage to return to normal within the time threshold.

[0084] The detailed structure of the offshore doubly-fed wind turbine fault ride-through control system is as Figure 5 shown.

[0085] Among them, the coordinated control module includes: a coordinated control calculation unit and a coordinated control unit;

[0086] The coordinated control calculation unit is used to calculate the injected active current and injected reactive current of the doubly-fed wind turbine during the low voltage duration according to the terminal voltage;

[0087] The coordinated control unit is based on the injected active current and injected reactive current during the low voltage duration to perform active and reactive power coordinated control.

[0088] Among them, the reactive power withdrawal module includes: a reactive power withdrawal calculation unit and a reactive power withdrawal control unit;

[0089] A reactive power withdrawal calculation unit, which is used to calculate the injected active current and injected reactive current during the reactive power support withdrawal period of the doubly-fed wind turbine according to the terminal voltage.

[0090] A reactive power withdrawal control unit, which is used to perform active and reactive power coordinated control based on the injected active current and injected reactive current during the reactive power support withdrawal period.

[0091] Wherein, the system further includes an initialization module for initialization, and the initialization module includes a design unit and a confirmation unit;

[0092] The design unit is used to design the active and reactive power coordinated control during the low-voltage duration of the offshore doubly-fed wind turbine based on the terminal voltage and the reactive power support withdrawal control in the post-fault clearing stage;

[0093] The confirmation unit is used to determine that the active and reactive power coordinated control during the low-voltage duration of the offshore doubly-fed wind turbine based on the terminal voltage and the reactive power support withdrawal control in the post-fault clearing stage operate normally in the control system of the offshore doubly-fed wind turbine.

[0094] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can adopt the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) containing computer-usable program code.

[0095] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of processes and / or blocks in the flowchart and / or block diagram can also be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for realizing the specified functions in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0096] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured product including an instruction device, and the instruction device realizes the processes Figure 1one process or multiple processes and / or blocks Figure 1 the functions specified in one block or multiple blocks.

[0097] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 the functions specified in one block or multiple blocks.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application rather than to limit the scope of its protection. Although the present application has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: after reading the present application, those skilled in the art can still make various changes, modifications or equivalent replacements to the specific implementation manners of the application. However, these changes, modifications or equivalent replacements are all within the scope of the protection of the pending claims of the application.

Claims

1. A fault ride-through control method for an offshore doubly-fed wind turbine, characterized in that: When a fault occurs, based on the collected terminal voltage of the offshore doubly-fed wind turbine, it is determined whether the terminal voltage is out of limit: If so, the offshore wind power grid-connected system enters the low-voltage duration period, and performs the pre-set active and reactive power coordinated control; Otherwise, when the time for the terminal voltage to return to normal is within the time threshold, the offshore wind power grid-connected system enters the post-fault clearance stage and performs the reactive power support withdrawal control; The execution of the reactive power support withdrawal control includes: Based on the terminal voltage, calculate the injected active current and injected reactive current during the reactive power support withdrawal period of the doubly-fed wind turbine; Based on the injected active current and injected reactive current during the reactive power support withdrawal period, perform the active and reactive power coordinated control; The calculation formula for the injected active current during the reactive power support withdrawal period is as follows: The calculation formula for the injected reactive current during the reactive power support withdrawal period is as follows: Among them, I p2 represents the injected active current during the reactive power support withdrawal period, L s represents the stator inductance of the doubly-fed wind turbine, L m represents the mutual inductance between the stator and rotor of the doubly-fed wind turbine, U T represents the terminal voltage, P ref represents the steady-state value of the active power; I q2 represents the injected reactive current during the reactive power support withdrawal period.

2. The method according to claim 1, wherein The determination of whether the terminal voltage is out of limit based on the collected terminal voltage of the offshore doubly-fed wind turbine includes: Judge whether the collected terminal voltage of the offshore doubly-fed wind turbine is less than or equal to the voltage threshold: If so, the terminal voltage is out of limit, otherwise the terminal voltage is not out of limit.

3. The method according to claim 1, wherein The execution of the pre-set active and reactive power coordinated control includes: Based on the terminal voltage, calculate the injected active current and injected reactive current during the low-voltage duration period of the doubly-fed wind turbine; Based on the injected active current and injected reactive current during the low-voltage duration period, perform the active and reactive power coordinated control.

4. The method according to claim 3, wherein The calculation formula for the injected reactive current during the low-voltage duration period is as follows: I q1 = 1.5(U e - U T )I N The calculation formula for the injected active current during the low-voltage duration period is as follows: Among them, I q1 represents the injected reactive current during the low-voltage duration, U e represents the voltage threshold, U T represents the terminal voltage, i N represents the rated current, I p1 represents the injected active current during the low-voltage duration, I max represents the maximum current value.

5. The method according to claim 1, characterized in that, Before the fault occurs: Design the active and reactive power coordinated control during the low-voltage duration period and the reactive power support withdrawal control in the post-fault clearance stage of the offshore doubly-fed wind turbine based on the terminal voltage; And determine that the active and reactive power coordinated control during the low-voltage duration period and the reactive power support withdrawal control in the post-fault clearance stage of the offshore doubly-fed wind turbine based on the terminal voltage operate normally in the control system of the offshore doubly-fed wind turbine.

6. A fault ride-through control system for an offshore doubly-fed wind turbine generator set, characterized in that, It includes: A judgment module, a coordinated control module and a reactive power withdrawal module; The judgment module is used to determine whether the terminal voltage is out of limit based on the collected terminal voltage of the offshore doubly-fed wind turbine when a fault occurs; The coordinated control module is used to perform the pre-set active and reactive power coordinated control when the terminal voltage is out of limit and the offshore wind power grid-connected system enters the low-voltage duration period; The reactive power withdrawal module is used to perform the reactive power support withdrawal control when the terminal voltage is not out of limit and the time for the terminal voltage to return to normal is within the time threshold and the offshore wind power grid-connected system enters the post-fault clearance stage; The reactive power withdrawal module includes: a reactive power withdrawal calculation unit and a reactive power withdrawal control unit; The reactive power withdrawal calculation unit is used to calculate the injected active current and injected reactive current during the reactive power support withdrawal period of the doubly-fed wind turbine based on the terminal voltage; The reactive power withdrawal control unit is used to perform active and reactive power coordinated control based on the injected active current and the injected reactive current during the reactive power support withdrawal period; The calculation formula for the injected active current during the reactive power support withdrawal period is as follows: The calculation formula for the injected reactive current during the reactive power support withdrawal period is as follows: Among them, i p2 represents the injected active current during the reactive power support withdrawal period, L s represents the stator inductance of the doubly-fed wind turbine generator, L m represents the mutual inductance between the stator and rotor of the doubly-fed wind turbine generator, U T represents the terminal voltage, P ref represents the steady-state value of the active power; I q2 represents the injected reactive current during the reactive power support withdrawal period.

7. The system according to claim 6, wherein The coordinated control module includes: a coordinated control calculation unit and a coordinated control unit; The coordinated control calculation unit is used to calculate the injected active current and the injected reactive current during the low voltage duration of the doubly-fed wind turbine according to the terminal voltage; The coordinated control unit performs active and reactive power coordinated control based on the injected active current and the injected reactive current during the low voltage duration.

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