Network construction type wind farm post-fault voltage recovery control method and system based on variable reactive power coefficient

Abstract

This invention discloses a voltage recovery control method and system for grid-connected wind farms after faults based on variable reactive power coefficients. The method includes: acquiring parameters of the grid-connected wind turbine generators and their operational requirements; determining the feasible region of reactive power output for the grid-connected wind turbine generators based on these parameters and operational requirements, combined with voltage-reactive power droop control constraints, and evaluating the maximum reactive power support and dynamic voltage support capabilities of the grid-connected wind turbine generators to obtain evaluation results; establishing an integrated model for voltage recovery control after faults involving the wind turbine generators, the wind farm, and the power grid, transforming the feasible region of reactive power output and the evaluation results into control constraints, and calculating the optimal reference value for the reactive power coefficient of the wind turbine generators to regulate each wind turbine generator. This invention aims to ensure the stability of node voltages in grid-connected wind farms under strong disturbances, maximize reactive power support and dynamic voltage support capabilities, and improve the voltage recovery control capability after wind farm faults.

Description

Technical Field

[0001] This invention mainly relates to the field of wind power generation technology, specifically to a voltage recovery control method and system for grid-type wind farms after a fault, based on variable reactive power coefficient. Background Technology

[0002] With the increasing proportion of wind power installed capacity, the voltage and reactive power support provided by wind farms during grid transient voltage faults have become important considerations for grid transient stability. Grid-connected wind turbines are prone to oscillation modes when the grid voltage suddenly expands or drops, leading to serious accidents such as large-scale grid disconnection. Therefore, it is necessary to study how to improve the transient voltage control capability of grid-connected wind farms.

[0003] Because grid-connected wind turbines experience power imbalance with the grid after a voltage dip fault, leading to power angle instability, their control strategy of maintaining voltage source characteristics can result in excessive short-circuit current output, posing an overcurrent risk to power electronic equipment. Furthermore, reactive power imbalance may cause a further voltage drop, triggering continuous high and low voltage ride-through faults. In severe cases, this could lead to large-scale equipment damage and grid-connected wind turbine off-grid accidents. Summary of the Invention

[0004] The technical problem to be solved by this invention is: In view of the technical problems existing in the prior art, this invention provides a voltage recovery control method and system for grid-connected wind farms after a fault, based on variable reactive power coefficient, which maximizes reactive power support and dynamic voltage support capabilities, improves the fault ride-through capability of grid-connected wind turbines and the fault recovery capability of power systems, while ensuring the stable output voltage of grid-connected wind turbines.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0006] A voltage recovery control method for grid-connected wind farms after a fault, based on variable reactive power coefficient, includes the following steps:

[0007] Obtain the parameters of grid-connected wind turbines and the operating requirements parameters of grid-connected wind turbines;

[0008] S2: Based on the parameters of the grid-type wind turbine and the operating requirements of the grid-type wind turbine, and combined with the voltage-reactive power droop control limit, determine the feasible domain of reactive power output of the grid-type wind turbine, and evaluate the maximum reactive power support and dynamic voltage support capabilities of the grid-type wind turbine to obtain the evaluation results.

[0009] S3: Establish an integrated model for voltage recovery control after grid-connected wind turbines, wind farms, and power grid faults. Transform the feasible region of reactive power output and evaluation results of grid-connected wind turbines into control constraints of the integrated model. Calculate the optimal reference value of reactive power coefficient for grid-connected wind turbines to regulate each grid-connected wind turbine.

[0010] Preferably, in step S1, the parameters of the grid-connected wind turbine include the rated voltage of the grid-connected wind turbine. The measured output voltage of the grid-side converter of the i-th grid-connected wind turbine unit. Output voltage phase angle and initial angular frequency Initial measured reactive power of the i-th grid-connected wind turbine reactive power droop coefficient Initial values, initial measured values ​​of active power and active droop coefficient Initial values; the operating requirements parameters for grid-connected wind turbines include the active power reference value, reactive power reference value, and grid connection point voltage reference value for each grid-connected wind turbine.

[0011] Preferably, in step S2, based on the parameters of the grid-connected wind turbine and the operating requirements parameters of the grid-connected wind turbine, and combined with voltage-reactive power droop control limitations, a control model for the grid-connected wind turbine is established, specifically as follows:

[0012] ;

[0013] In the formula, and These are the output voltage phase angle and initial angular frequency of the grid-side converter of the i-th grid-connected wind turbine, respectively. and These are the active power droop coefficient and reactive power droop coefficient of the i-th grid-connected wind turbine, respectively. and These are the baseline active power value and the measured active power value of the i-th grid-connected wind turbine, respectively. and These are the voltage reference value and the output voltage measurement value generated by the grid-side converter of the i-th grid-connected wind turbine, respectively. and These are the baseline value and measured value of reactive power for the i-th grid-type wind turbine, respectively.

[0014] The reactive power droop coefficient Treating them as variable, the dynamic behavior model of reactive power regulation of grid-connected wind turbines is derived from the voltage-reactive power relationship in the control model of grid-connected wind turbines as follows:

[0015] ;

[0016] In the formula, and These represent the increments of the measured reactive power value and the reactive power reference value for the i-th grid-connected wind turbine, respectively. and These are the reference voltage increment and the initial reference voltage value of the grid-side converter of the i-th grid-connected wind turbine, respectively.

[0017] The reactive power model of n grid-connected wind turbines in a wind farm is represented as follows:

[0018] ;

[0019] In the formula,

[0020] ;

[0021] ;

[0022] ;

[0023] ;

[0024] for The derivative, Let be the time constant of the first-order inertial element of the nth grid-connected wind turbine.

[0025] The maximum available reactive power is calculated based on the grid-side converter capacity and active power measurements of each wind turbine grid type. and minimum value To obtain the feasible domain of reactive power output for each grid-type wind turbine;

[0026] Based on the maximum reactive power that can be utilized by the i-th grid-connected wind turbine. Calculate the total maximum reactive power support capacity of the wind farm. : ;

[0027] Define the maximum reactive power support capacity assessment index : ;

[0028] Based on the dynamic behavior model of reactive power regulation of grid-connected wind turbines, the dynamic voltage support coefficient of the i-th grid-connected wind turbine is defined. : ;

[0029] Dynamic voltage support capability assessment indicators for: ;in, For reference, the dynamic support coefficient;

[0030] Calculate the overall evaluation result M: Where α and β are weighting coefficients, satisfying α + β = 1;

[0031] The assessment results include: maximum reactive power support capacity index Dynamic voltage support capability index Comprehensive evaluation results M.

[0032] Preferably, in step S3, the specific process of establishing the integrated model for voltage recovery control after a grid-connected wind turbine generator-wind farm-grid fault is as follows:

[0033] S3.1: Construct the continuous-time state equation for reactive power control of grid-connected wind turbine units;

[0034] S3.2: Set the sampling time as The continuous-time state equation of reactive power control is discretized to obtain the discrete-time state equation of reactive power control, which serves as the basic framework of the integrated model of voltage recovery control after grid-connected wind turbine, wind farm and grid fault.

[0035] S3.3: Based on the reactive power control discrete-time state equation obtained in S3.2, and combined with the incremental reactive power model with droop control, the output of the reactive power control discrete-time state equation is changed from reactive power command to droop coefficient command. A reactive power-adaptive droop control model is constructed, forming the final integrated model of grid-connected wind turbine-wind farm-grid voltage recovery control after fault.

[0036] Preferably, in S3.1, the continuous state-space equations for reactive power control of n grid-type wind turbine generators in a grid-type wind farm are constructed as follows:

[0037] ;

[0038] In the formula,

[0039] ;

[0040] ;

[0041] ;

[0042] ;

[0043] ;

[0044] ;

[0045] In the formula, and These represent the increments of the reactive power measurement value and the reactive power reference value for the nth grid-connected wind turbine, respectively. It is the identity matrix. Let be the time constant of the first-order inertial element of the nth grid-connected wind turbine. for The derivative of .

[0046] Preferably, in S3.2, the basic framework of the integrated model for voltage recovery control after a grid-connected wind turbine-wind farm-grid fault is represented as follows:

[0047] ;

[0048] In the formula, k represents the k-th time step. , .

[0049] Preferably, in step S3.3, according to the requirements of the power grid specifications, the response time of each grid-connected wind turbine is relatively short during the transient voltage ride-through process. Based on the optimized droop coefficient, an optimal droop control scheme is designed to achieve rapid reactive power sharing among grid-connected wind turbines. The incremental reactive power model with droop control is expressed as follows:

[0050] ;

[0051] in, , and These represent the initial measured reactive power, reactive power droop coefficient, and output voltage measured value of the i-th grid-connected wind turbine, respectively. This refers to the rated voltage of grid-connected wind turbine units;

[0052] The output of the discrete-time state equation for reactive power control of grid-connected wind turbines is changed from a reactive power command to a droop coefficient command:

[0053] ;

[0054] In the formula,

[0055] ;

[0056] ;

[0057] ;

[0058] The discrete state-space model of a wind farm with droop control is determined as follows:

[0059] ;

[0060] The reactive power-adaptive droop control model is progressively constructed from the incremental reactive power model with droop control, the discrete-time state equation of reactive power control for grid-type wind turbines, and the discrete state-space model of wind farms with droop control.

[0061] Preferably, the objective function of the reactive power-adaptive droop control model is:

[0062]

[0063] in,

[0064]

[0065]

[0066] In the formula, The rated voltage of the grid-connected wind turbine unit, and These are the voltage reference value and the output voltage measurement value generated by the grid-side converter of the i-th grid-connected wind turbine, respectively. Let be the sensitivity coefficient of the voltage of the i-th grid-connected wind turbine to the active power output of the n-th wind turbine. Let be the sensitivity coefficient of the voltage of the i-th grid-connected wind turbine to the reactive power output of the n-th wind turbine;

[0067] The control constraints of the integrated model are:

[0068] The reactive power reference value of a grid-connected wind turbine is related to the measured terminal voltage and droop factor of the wind turbine generator. Therefore, the reactive power droop factor K... gi The constraint is to ensure that the reactive power of grid-connected wind turbines does not exceed the available reactive power limit:

[0069] ;

[0070] In the formula, K gi It is the reactive power droop coefficient of the i-th grid-connected wind turbine unit; and These are the minimum and maximum values ​​of the reactive power that the i-th grid-connected wind turbine can utilize, respectively.

[0071] The present invention also discloses a voltage recovery control system for grid-type wind farms after a fault based on variable reactive power coefficient, including a memory and a processor. The memory stores a computer program, and the computer program is executed by the processor to perform the steps of the method described above.

[0072] Compared with the prior art, the advantages of the present invention are as follows:

[0073] This invention determines the feasible region of reactive power output of grid-connected wind turbines, evaluates the reactive power support and transient voltage support capabilities of grid-connected wind turbines, establishes an integrated voltage recovery control model after a grid-connected wind turbine-wind farm-grid fault, transforms the feasible region of reactive power output into constraints for the model control algorithm, ensures the stability of the output voltage of grid-connected wind turbines during continuous fault ride-through, reduces the terminal voltage deviation of grid-connected wind turbines, and improves the continuous fault ride-through capability of grid-connected wind turbines. Attached Figure Description

[0074] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0075] Figure 1 This is a flowchart of the voltage recovery control method for grid-type wind farms based on variable reactive power coefficient according to the present invention.

[0076] Figure 2 Voltage control topology diagram of wind turbine generators in a grid-type wind farm. Detailed Implementation

[0077] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0078] like Figure 1 As shown in the figure, the voltage recovery control method for grid-type wind farms based on variable reactive power coefficient according to an embodiment of the present invention includes the following steps:

[0079] S1: Obtain the parameters and operating requirements of grid-connected wind turbines; among which, the parameters of grid-connected wind turbines include the rated voltage of the grid-connected wind turbines. Measured output voltage values ​​of grid-side converters for each grid-type wind turbine. Output voltage phase angle and initial angular frequency Initial measured values ​​of reactive power of wind turbines of various grid types reactive power droop coefficient Initial values, initial measured values ​​of active power and active droop coefficient Initial values: the initial maximum and minimum values ​​of reactive power available for each grid-type wind turbine; the operating requirements parameters for grid-type wind turbines include the active power reference value, reactive power reference value, grid connection point voltage reference value, and reactive current injection requirements during faults for each grid-type wind turbine.

[0080] S2: Based on the parameters of the grid-type wind turbine and the operating requirements of the grid-type wind turbine, and combined with the voltage-reactive power droop control limit, determine the feasible domain of reactive power output of the grid-type wind turbine, and evaluate the maximum reactive power support and dynamic voltage support capabilities of the grid-type wind turbine to obtain the evaluation results.

[0081] In this embodiment, in step S2, based on the obtained parameters of the grid-connected wind turbine and the operating requirements parameters of the grid-connected wind turbine, and combined with the voltage-reactive power droop control limit, a reactive power control model for the grid-connected wind turbine is established. The dynamic behavior and time delay of the reactive power regulation of the grid-connected wind turbine can be expressed as follows:

[0082]

[0083] In the formula, and These are the output voltage phase angle and initial angular frequency of the grid-side converter of the i-th grid-connected wind turbine, respectively. and These are the active power droop coefficient and reactive power droop coefficient of the i-th grid-connected wind turbine, respectively. and These are the baseline active power value and the measured active power value of the i-th grid-connected wind turbine, respectively. and These are the voltage reference value and the output voltage measurement value generated by the grid-side converter of the i-th grid-connected wind turbine, respectively. and These are the baseline value and measured value of reactive power for the i-th grid-type wind turbine, respectively.

[0084] Treating the reactive power output voltage droop coefficient as a variable, the dynamic behavior model of reactive power regulation of grid-connected wind turbines is derived from the voltage-reactive power relationship in the above equation as follows:

[0085]

[0086] In the formula, and These represent the increments of the measured reactive power value and the reactive power reference value for the i-th grid-connected wind turbine, respectively. and These are the reference voltage increment and the initial reference voltage value of the grid-side converter of the i-th grid-connected wind turbine, respectively.

[0087] The reactive power model of n grid-connected wind turbines in a wind farm is represented as follows:

[0088] ;

[0089] In the formula,

[0090] ;

[0091] ;

[0092] ;

[0093] ;

[0094] for The derivative of Let be the time constant of the first-order inertial element of the nth grid-connected wind turbine.

[0095] The maximum available reactive power is calculated based on the grid-side converter capacity and active power measurements of each wind turbine grid type. and minimum value To obtain the feasible region of reactive power output for each grid-type wind turbine. , ]; and The following formula is used to calculate:

[0096] ,

[0097] in, The maximum available capacity of the grid-side converter of the i-th grid-type wind turbine unit;

[0098] Based on the maximum reactive power that can be utilized by the i-th grid-connected wind turbine. Calculate the total maximum reactive power support capacity of the wind farm. : ;

[0099] Define the maximum reactive power support capacity assessment index : ;

[0100] Based on the dynamic behavior model of reactive power regulation of grid-connected wind turbines, the dynamic voltage support coefficient of the i-th grid-connected wind turbine is defined. : ;

[0101] Dynamic voltage support capability assessment indicators for: ;in, For reference, the dynamic support coefficient;

[0102] Calculate the overall evaluation result M: Where α and β are weighting coefficients, satisfying α + β = 1;

[0103] The assessment results include: maximum reactive power support capacity index Dynamic voltage support capability index Comprehensive evaluation results M.

[0104] The main purpose of the assessment is to transform the assessment results into quantitative values, providing constraints for the subsequent objective function, and the maximum reactive power support capacity index. If ≤1, the dynamic support requirements and dynamic voltage support capability index are met. If the value is ≤1, the dynamic support requirements are met. The comprehensive evaluation result M is assigned α and β weight coefficients based on transient and steady-state conditions. If the value is less than or equal to 1, the maximum reactive power support and dynamic voltage support requirements are met.

[0105] S3: Establish an integrated model for voltage recovery control after grid-connected wind turbines, wind farms, and power grid faults. Transform the obtained feasible region and evaluation results of reactive power output of grid-connected wind turbines into control constraints of the integrated model. Calculate the optimal reference value of reactive power coefficient for grid-connected wind turbines to regulate each grid-connected wind turbine.

[0106] In step S3, the specific process of establishing an integrated model for voltage recovery control after a grid-connected wind turbine, wind farm, and power grid fault is as follows:

[0107] S3.1: First, construct the continuous-time state equation for reactive power control of the grid-connected wind turbine:

[0108] The state-space equations for reactive power control of a grid-connected wind farm are established. The continuous state-space equations for reactive power control of n grid-connected wind turbine generators are as follows:

[0109] ;

[0110] In the formula,

[0111] ;

[0112] ;

[0113] ;

[0114] ;

[0115] ;

[0116] ;

[0117] In the formula, and These represent the increments of the reactive power measurement value and the reactive power reference value for the nth grid-connected wind turbine, respectively. It is the identity matrix. Let be the time constant of the first-order inertial element of the nth grid-connected wind turbine. for The derivative of .

[0118] S3.2: Set the sampling time as The continuous-time state equation for reactive power control is discretized to obtain the discrete-time state equation for reactive power control. This serves as the basic framework for the integrated model of voltage recovery control after a grid-connected wind turbine, wind farm, and power grid fault. Specifically:

[0119] ;

[0120] In the formula, k represents the k-th time step. , .

[0121] S3.3: Based on the reactive power control discrete-time state equation obtained in S3.2, and combined with the incremental reactive power model with droop control, the output of the reactive power control discrete-time state equation is changed from reactive power command to droop coefficient command. A reactive power-adaptive droop control model is constructed, forming the final integrated model for voltage recovery control after grid-connected wind turbines, wind farms, and grid faults. According to grid specifications, during transient voltage ride-through, the response time of each grid-connected wind turbine is relatively short. Based on the optimized droop coefficient, an optimal droop control scheme is designed, achieving rapid reactive power sharing among grid-connected wind turbines. The incremental reactive power model with droop control can be expressed as:

[0122] ;

[0123] in, , and These represent the initial measured reactive power, reactive power droop coefficient, and output voltage measured value of the i-th grid-connected wind turbine, respectively. This refers to the rated voltage of grid-connected wind turbine units;

[0124] The output of the discrete-time state equation for reactive power control of grid-connected wind turbines is changed from a reactive power command to a droop coefficient command:

[0125] ;

[0126] In the formula,

[0127] ;

[0128] ;

[0129] ;

[0130] The discrete state-space model (i.e., the operating controller) of the wind farm with droop control is determined as follows:

[0131] ;

[0132] The reactive power-adaptive droop control model is progressively constructed from the incremental reactive power model with droop control, the discrete-time state equation of reactive power control for grid-type wind turbines, and the discrete state-space model of wind farms with droop control.

[0133] The objective function of the controller is:

[0134] ;

[0135] in,

[0136] ;

[0137] ;

[0138] ;

[0139] ;

[0140] In the formula, The rated voltage of the grid-connected wind turbine unit, and These are the voltage reference value and the output voltage measurement value generated by the grid-side converter of the i-th grid-connected wind turbine, respectively. Let be the sensitivity coefficient of the voltage of the i-th grid-connected wind turbine to the active power output of the n-th wind turbine. Let be the sensitivity coefficient of the voltage of the i-th grid-connected wind turbine to the reactive power output of the n-th wind turbine; and These represent the increments of the reactive power measurement value and the active power measurement value of the i-th grid-connected wind turbine, respectively.

[0141] The objective function aims to ensure that the voltage of each unit in the wind farm remains stable and follows the reference value during transient periods, thus ensuring that the grid-connected wind turbines do not disconnect from the grid.

[0142] In step S3, the reactive power reference value of the grid-connected wind turbine is related to the measured terminal voltage and droop factor of the wind turbine. Therefore, the reactive power droop factor K gi The constraint is to ensure that the reactive power of grid-connected wind turbines does not exceed the available reactive power limit:

[0143] ;

[0144] In the formula, K giIt is the reactive power droop coefficient of the i-th grid-connected wind turbine unit; and These are the minimum and maximum values ​​of the reactive power that the i-th grid-connected wind turbine can utilize, respectively.

[0145] By adjusting the optimal reactive power control droop coefficient reference value, the wind turbines of each grid configuration are controlled to ensure that the transient voltage of the wind farm meets the control requirements. In actual implementation, iterative control is achieved by iteratively executing steps S1-S3.

[0146] This invention employs a model predictive control algorithm to calculate the converter current reference value, which can solve the optimization control problem of multi-input multi-output systems and obtain the optimal open-loop control result.

[0147] The voltage control topology diagram of the wind turbine generator in the grid-type wind farm of this invention is as follows: Figure 2 V in the figure gs k represents the grid voltage amplitude. p k i T represents the proportional gain and integral gain of the outer-loop PI controller. ig T is the inner loop time constant. fg This is the time constant of the reactive power filter.

[0148] This invention is applicable to voltage control operation under transient faults in grid-connected wind farms. Based on model predictive control, it optimizes the reactive power output and voltage support capabilities of grid-connected wind turbines within the feasible region of reactive power regulation by optimizing the reference value of the reactive power control coefficient of the grid-connected wind turbines, while ensuring that the grid-connected wind turbines do not disconnect from the grid. This fully taps the fault support potential of the grid-connected wind turbines and enhances their active voltage and reactive power support capabilities.

[0149] This invention addresses the issue of suppressing generator voltage fluctuations by coordinating the reactive power control coefficients of wind turbine units during sudden rises or falls in grid voltage. While ensuring stable output voltage, it determines the reactive power operating safety domain based on parameters collected from grid-connected wind turbine units. By optimizing the reference values ​​of the reactive power control coefficients, it minimizes transient voltage fluctuations, thereby improving the transient voltage support capability and continuous fault ride-through capability of grid-connected wind turbine units.

[0150] This invention determines the feasible region of reactive power output of grid-connected wind turbines, evaluates the reactive power support and transient voltage support capabilities of grid-connected wind turbines, establishes an integrated voltage recovery control model after a grid-connected wind turbine-wind farm-grid fault, transforms the feasible region of reactive power output into constraints for the model control algorithm, ensures the stability of the output voltage of grid-connected wind turbines during continuous fault ride-through, reduces the terminal voltage deviation of grid-connected wind turbines, and improves the continuous fault ride-through capability of grid-connected wind turbines.

[0151] The present invention also discloses a voltage recovery control system for grid-type wind farms after a fault based on variable reactive power coefficient, including a memory and a processor. The memory stores a computer program, and the computer program is executed by the processor to perform the steps of the method described above.

[0152] The present invention can implement all or part of the processes in the methods of the above embodiments, or it can be implemented by hardware related to computer program instructions. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, it can implement the steps of the above method embodiments. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or some intermediate form. The computer-readable storage medium includes: any entity or device capable of carrying computer program code, recording media, USB flash drive, portable hard drive, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. The memory is used to store computer programs and / or modules. The processor implements various functions by running or executing the computer programs and / or modules stored in the memory, and by calling data stored in the memory. The memory may include high-speed random access memory, as well as non-volatile memory, such as hard disks, RAM, plug-in hard disks, smart media cards (SMC), secure digital (SD) cards, flash cards, at least one disk storage device, flash memory device, or other volatile solid-state storage devices.

[0153] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principle of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A voltage recovery control method for grid-type wind farms after a fault, based on variable reactive power coefficient, characterized in that, Including the following steps: S1: Obtain the parameters of grid-connected wind turbines and the operating requirements parameters of grid-connected wind turbines; S2: Based on the parameters of the grid-type wind turbine and the operating requirements of the grid-type wind turbine, and combined with the voltage-reactive power droop control limit, determine the feasible domain of reactive power output of the grid-type wind turbine, and evaluate the maximum reactive power support and dynamic voltage support capabilities of the grid-type wind turbine to obtain the evaluation results. S3: Establish an integrated model for voltage recovery control after grid-connected wind turbines, wind farms, and power grid faults. Transform the feasible region of reactive power output and evaluation results of grid-connected wind turbines into control constraints of the integrated model. Calculate the optimal reference value of reactive power coefficient for grid-connected wind turbines to regulate each grid-connected wind turbine.

2. The voltage recovery control method for grid-connected wind farms based on variable reactive power coefficient for droop-controlled grid-connected units according to claim 1, characterized in that, In step S1, the parameters of the grid-connected wind turbine include the rated voltage of the grid-connected wind turbine, the measured output voltage, output voltage phase angle and initial angular frequency of the grid-side converter of the i-th grid-connected wind turbine, and the initial measured reactive power, initial reactive power droop coefficient, initial measured active power and initial active power droop coefficient of the i-th grid-connected wind turbine. The operating requirements parameters of the grid-connected wind turbine include the reference values ​​of active power, reactive power and grid connection point voltage for each grid-connected wind turbine.

3. The voltage recovery control method and system for grid-type wind farms based on variable reactive power coefficients after a fault, as described in claim 2, is characterized in that... In step S2, based on the parameters of the grid-connected wind turbine and its operational requirements, and combined with voltage-reactive power droop control limitations, a control model for the grid-connected wind turbine is established, specifically as follows: ； In the formula, and These are the output voltage phase angle and initial angular frequency of the grid-side converter of the i-th grid-connected wind turbine, respectively. and These are the active power droop coefficient and reactive power droop coefficient of the i-th grid-connected wind turbine, respectively. and These are the baseline active power value and the measured active power value of the i-th grid-connected wind turbine, respectively. and These are the voltage reference value and the output voltage measurement value generated by the grid-side converter of the i-th grid-connected wind turbine, respectively. and These are the baseline value and measured value of reactive power for the i-th grid-type wind turbine, respectively.

4. The voltage recovery control method for grid-type wind farms based on variable reactive power coefficient according to claim 3, characterized in that, In step S2, the reactive power droop coefficient is... Treating them as variable, the dynamic behavior model of reactive power regulation of grid-connected wind turbines is derived from the voltage-reactive power relationship in the control model of grid-connected wind turbines as follows: ； In the formula, and These represent the increments of the measured reactive power value and the reactive power reference value for the i-th grid-connected wind turbine, respectively. and These are the reference voltage increment and the initial reference voltage value of the grid-side converter of the i-th grid-connected wind turbine, respectively. The reactive power model of n grid-connected wind turbines in a wind farm is represented as follows: ； In the formula, ； ； ； ； for The derivative of Let be the time constant of the first-order inertial element of the nth grid-connected wind turbine. The maximum available reactive power is calculated based on the grid-side converter capacity and active power measurements of each wind turbine grid type. and minimum value To obtain the feasible domain of reactive power output for each grid-type wind turbine; Based on the maximum reactive power that can be utilized by the i-th grid-connected wind turbine. Calculate the total maximum reactive power support capacity of the wind farm. : ; Define the maximum reactive power support capacity assessment index : ; Based on the dynamic behavior model of reactive power regulation of grid-connected wind turbines, the dynamic voltage support coefficient of the i-th grid-connected wind turbine is defined. : ; Dynamic voltage support capability assessment indicators for: ;in, For reference, the dynamic support coefficient; Calculate the overall evaluation result M: Where α and β are weighting coefficients, satisfying α+β=1.

5. The voltage recovery control method for grid-type wind farms based on variable reactive power coefficients according to any one of claims 1-4, characterized in that, In step S3, the specific process of establishing an integrated model for voltage recovery control after a grid-connected wind turbine, wind farm, and power grid fault is as follows: S3.1: Construct the continuous-time state equation for reactive power control of grid-connected wind turbine units; S3.2: Set the sampling time as The continuous-time state equation of reactive power control is discretized to obtain the discrete-time state equation of reactive power control, which serves as the basic framework for the integrated model of voltage recovery control after grid-connected wind turbine, wind farm and grid fault. S3.3: Based on the reactive power control discrete-time state equation obtained in S3.2, and combined with the incremental reactive power model with droop control, the output of the reactive power control discrete-time state equation is changed from reactive power command to droop coefficient command. A reactive power-adaptive droop control model is constructed, forming the final integrated model of grid-connected wind turbine-wind farm-grid voltage recovery control after fault.

6. The voltage recovery control method for grid-type wind farms based on variable reactive power coefficient according to claim 5, characterized in that, In S3.1, the continuous state-space equations for reactive power control of n grid-connected wind turbines in a grid-connected wind farm are constructed as follows: ； In the formula, ； ； ； ； ； ； In the formula, and These represent the increments of the reactive power measurement value and the reactive power reference value for the nth grid-connected wind turbine, respectively. It is the identity matrix. Let be the time constant of the first-order inertial element of the nth grid-connected wind turbine. for The derivative of .

7. The voltage recovery control method for grid-type wind farms based on variable reactive power coefficients according to claim 6, characterized in that, In S3.2, the basic framework of the integrated model for voltage recovery control after a grid-connected wind turbine, wind farm, and power grid fault is represented as follows: ； In the formula, k represents the k-th time step. , .

8. The voltage recovery control method for grid-type wind farms based on variable reactive power coefficients according to claim 7, characterized in that, S3.3 specifically includes establishing an incremental reactive power model with droop control, expressed as: ； in, , and These represent the initial measured reactive power, reactive power droop coefficient, and output voltage measured value of the i-th grid-connected wind turbine, respectively. This refers to the rated voltage of a grid-connected wind turbine. The output of the discrete-time state equation for reactive power control of grid-connected wind turbines is changed from a reactive power command to a droop coefficient command: ； In the formula, ； ； ； The discrete state-space model of a wind farm with droop control is determined as follows: ； The reactive power-adaptive droop control model is progressively constructed from the incremental reactive power model with droop control, the discrete-time state equation of reactive power control for grid-type wind turbines, and the discrete state-space model of wind farms with droop control.

9. The voltage recovery control method for grid-type wind farms based on variable reactive power coefficient according to claim 5, characterized in that, The objective function of the reactive power-adaptive droop control model is: ； in, ； ； ； ； In the formula, The rated voltage of the grid-connected wind turbine unit, and These are the voltage reference value and the output voltage measurement value generated by the grid-side converter of the i-th grid-connected wind turbine, respectively. Let be the sensitivity coefficient of the voltage of the i-th grid-connected wind turbine to the active power output of the n-th wind turbine. Let be the sensitivity coefficient of the voltage of the i-th grid-connected wind turbine to the reactive power output of the n-th wind turbine; and These represent the increments of the reactive power measurement value and the active power measurement value of the i-th grid-connected wind turbine unit, respectively. The control constraints of the integrated model are: The constraint of the reactive power droop factor is to ensure that the reactive power of grid-connected wind turbines does not exceed the available reactive power limit: ； In the formula, K gi It is the reactive power droop coefficient of the i-th grid-connected wind turbine unit; and These are the minimum and maximum values ​​of the reactive power that can be utilized by the i-th grid-connected wind turbine, respectively.

10. A voltage recovery control system for grid-connected wind farms after a fault, characterized in that, It includes a memory and a processor, wherein the memory stores a computer program, and the computer program is executed by the processor to perform the steps of the method as described in any one of claims 1-9.

Images