Method for improving active power transmission capability of wind turbine generator under asymmetric fault

Abstract

The invention discloses a method for improving the active power transmission capability of a wind turbine generator under an asymmetric fault, and aims to solve the problems that the active power transmission capability of the wind turbine generator under the asymmetric fault in the prior art is limited, overcurrent, overvoltage and transient instability are easy to occur and the like. The method comprises the following steps: firstly, establishing an optimal active power transmission capability improvement model comprising rotor current, rotor voltage, voltage unbalance degree and transient stability constraint; secondly, performing convexity processing on the non-convex model through double-sequence coordinate system reconstruction, positive semidefinite relaxation and other technologies, and ensuring global optimality of a solution; and finally, adaptively coordinating active power transmission lifting and voltage unbalance suppression according to actual power limitation. According to the method, the power and the current capacity of the wind turbine generator can be fully utilized, the active power output capacity under the asymmetric fault is remarkably improved on the premise that safe and stable operation is ensured, and voltage unbalance is effectively restrained. And a reference is provided for improving the active power transmission capability under the asymmetric fault of the wind turbine generator.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation control, and in particular to a method for improving the active power transmission capability of a wind power generator set based on a doubly-fed induction generator under a grid asymmetric fault condition. Background Art

[0002] With the gradual replacement of large-scale synchronous generators, renewable energy resources (RES) are required to maintain active power transfer capability (APTC) even during grid faults to reduce the risk of power supply shortages. However, compared with symmetrical faults, asymmetrical faults pose a severe challenge to the active power transfer capability of renewable energy, especially doubly-fed wind turbines.

[0003] Reference ①[Z. Wang et al. PLL Synchronization Transient Stability Analysis of a Weak-Grid Connected VSC During Asymmetric Faults[J]. IEEE Transactions on Power Electronics, 2024,39(2): 2140-2154.] points out that when the fault location is close to the common connection point, the double-sequence coupling effect cannot be ignored. Due to the double-sequence coupling effect, the transient stability feasible region considering positive-sequence and negative-sequence currents will interact with each other. Reference = 2 \* GB3 ②[Y. Feng, W. Huang, Z. Jin, Y. Li, ZJShen and Z. Shuai. Voltage Support Strategy for Improving Power TransferCapability of Grid-Connected Converter Under Unbalanced Conditions[J]. IEEE Transactions on Power Electronics, 2024,39(7): 7863-7875.] proposes a negative-sequence voltage compensation strategy to increase the output active power, in which less negative-sequence current is injected into the grid to attenuate the voltage imbalance. Reference = 3 \* GB3 ③[H. Zhang, R. Liu, C. Xue and Y. Li. Active Power EnhancementControl Strategy of Grid-Forming Inverters Under Asymmetrical Grid Faults[J].IEEE Transactions on Power Electronics, 2024,39(1): 1447-1459.] points out that the power angle in the dual-sequence network is the key factor affecting APTC, and proposes an accurate voltage compensation strategy based on controllable dual-sequence power angle.

[0004] Previous research has primarily focused on enhancing APTC in conventional grid-connected converters. However, the structure and control methods of wind turbines based on doubly fed induction generators (DFIGs) differ significantly, primarily due to their rotor-side converters (RSCs). Further exploration of the active power margin of DFIG wind turbines still presents the following challenges in optimal current command design: i) Due to the high back electromotive force (BEM) induced by the counter-rotating negative-sequence flux, DFIGs are susceptible to overcurrent, overmodulation, and transient instability. ii) Asymmetric faults introduce multivariable coupling, and nonlinear transformations exist between the stator and rotor physical quantities in DFIGs. The nonconvexity resulting from the dual-sequence coupling effect and the inherent slip characteristics complicates the optimization problem.

[0005] Therefore, how to design an effective control strategy to maximize the active power transmission capability of DFIG under asymmetric faults while satisfying various safety constraints and taking into account the suppression of voltage imbalance is a technical problem that needs to be solved urgently. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for improving the active power transmission capability of a wind turbine under asymmetric faults, so as to solve the problems mentioned in the background technology of limited active power transmission of DFIG under asymmetric faults, difficulty in solving non-convex models, and difficulty in coordinating active power enhancement and voltage imbalance suppression.

[0007] According to a first aspect of an embodiment of the present application, a method for improving the active power transmission capability of a wind turbine generator set under an asymmetric fault is provided, comprising: Establishing an optimal active power transmission capability improvement model for a doubly-fed wind turbine generator system under asymmetric faults, the model includes an objective function, rotor current constraints, rotor voltage constraints, voltage imbalance constraints, and transient stability constraints; Based on the optimal active power transmission capacity improvement model, the positive sequence and negative sequence synchronous rotation coordinate systems are d The axes are unified to the grid voltage orientation mode and the dual-sequence synchronous rotating coordinate system is reconstructed to eliminate the nonlinearity and coupling characteristics caused by the dual-sequence power angle coupling term; Based on the electrical quantities after the dual-sequence synchronous rotation coordinate system, a second-order cone relaxation transformation is performed on the rotor current constraint and the rotor voltage constraint, a semi-positive definite relaxation transformation is performed on the voltage imbalance constraint, an augmented matrix variable is constructed and a rank constraint is introduced to form a standard semi-positive definite programming problem; Based on the semi-positive definite programming model, according to the actual active power limit, the active power transmission capacity improvement and voltage imbalance suppression are adaptively coordinated, and the limit value of the voltage imbalance constraint is iteratively adjusted until the calculated active power is less than or equal to the actual active power limit.

[0008] According to a second aspect of an embodiment of the present application, a device for improving the active power transmission capability of a wind turbine generator set under an asymmetric fault is provided, comprising: A model building module is used to establish an optimal active power transmission capability improvement model for a doubly-fed wind turbine generator system under asymmetric faults, wherein the model includes an objective function, rotor current constraints, rotor voltage constraints, voltage imbalance constraints, and transient stability constraints; The first convex processing module is used to synchronously rotate the positive sequence and negative sequence coordinate systems based on the optimal active power transmission capability improvement model. d The axes are unified to the grid voltage orientation mode and the dual-sequence synchronous rotating coordinate system is reconstructed to eliminate the nonlinearity and coupling characteristics caused by the dual-sequence power angle coupling term; A second convexification processing module is configured to perform a second-order cone relaxation transformation on the rotor current constraint and the rotor voltage constraint based on the electrical quantities after the dual-order synchronous rotation coordinate system, perform a semi-positive definite relaxation transformation on the voltage imbalance constraint, construct an augmented matrix variable, and introduce a rank constraint to form a standard semi-positive definite programming problem; An adaptive solution module is used to adaptively coordinate the improvement of active power transmission capability and the suppression of voltage imbalance based on the semi-definite programming model and the actual active power limit, and iteratively adjust the limit value of the voltage imbalance constraint until the calculated active power is less than or equal to the actual active power limit.

[0009] According to a third aspect of an embodiment of the present application, there is provided an electronic device, characterized by comprising: one or more processors; a memory for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in the first aspect.

[0010] According to a fourth aspect of an embodiment of the present application, a computer-readable storage medium is provided, on which computer instructions are stored. When the instructions are executed by a processor, the steps of the method described in the first aspect are implemented.

[0011] The technical solutions provided by the embodiments of the present application may have the following beneficial effects: As can be seen from the above examples, this application establishes an optimal active power transmission capacity improvement model, which includes an objective function, rotor current constraints, rotor voltage constraints, voltage imbalance constraints, and transient stability constraints. This effectively prevents overcurrent and overmodulation caused by high negative-sequence electromotive force, ensures the stable equilibrium point of the dual-sequence phase-locked loop, and improves the safety of system operation. Through convexification techniques such as dual-sequence coordinate system reconstruction and semi-positive relaxation, the non-convexity problems introduced by the inherent slip characteristics of the DFIG and the dual-sequence coupling effect are effectively resolved, ensuring the global optimality or high-quality approximation of the optimization solution. Geometric analysis reveals the mutual constraint relationship between VUF suppression and APTC improvement, and designs an adaptive coordination mechanism that can flexibly adjust the priority of the two objectives while considering actual power constraints, fully utilizing the power and current capacity of the DFIG. The proposed method can significantly improve the active power transmission capacity of the DFIG under asymmetric faults while maintaining effective VUF suppression capabilities. The above is the method we provide.

[0012] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0014] Figure 1 The present invention is a flow chart showing a method for improving the active power transmission capability of a wind turbine generator system under an asymmetric fault according to an exemplary embodiment.

[0015] Figure 2 The diagram is a topology and control block diagram of a doubly-fed wind turbine system under an asymmetric fault according to an embodiment of the present invention.

[0016] Figure 3 FIG. 4 is a schematic diagram of dual-sequence coordinate system reconstruction of a doubly-fed wind turbine generator system according to an embodiment of the present invention.

[0017] Figure 4 FIG. 4 is a geometric diagram illustrating the relationship between active power transmission capability improvement and voltage imbalance suppression according to an embodiment of the present invention.

[0018] Figure 5 FIG. 4 is an algorithm flow chart of the method of the present invention according to an embodiment of the present invention.

[0019] Figure 6 The present invention is a block diagram showing a device for improving the active power transmission capability of a wind turbine generator system under an asymmetric fault condition according to an exemplary embodiment. DETAILED DESCRIPTION

[0020] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0021] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. As used in this application and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0022] Figure 1 FIG. 1 is a flow chart showing a method for improving the active power transmission capability of a wind turbine generator system under an asymmetric fault according to an exemplary embodiment. Figure 1 As shown, the method may include the following steps: S1: Establishing an optimal active power transmission capability improvement model for a doubly-fed wind turbine generator system under asymmetric faults, wherein the model includes an objective function, rotor current constraints, rotor voltage constraints, voltage imbalance constraints, and transient stability constraints; Specifically, Figure 2 The following is a block diagram of the system topology and control of a doubly-fed wind turbine generator system under an asymmetric fault condition according to an embodiment of the present invention. The control of the DFIG includes a synchronization unit and a dual-sequence current control unit. The commonly used decoupled double synchronous reference frame phase lock loop (DDSRF-PLL) is used as the synchronization unit. Increasing the stator output active power of the DFIG through RSC is the key to enhancing the APTC of the DFIG and is also the focus of the present invention. Since the grid-side converter (GSC) mainly maintains a constant DC bus voltage, the present invention simplifies the analysis by equating the GSC to a constant DC voltage.

[0023] When an asymmetric fault occurs (including single-phase grounding, two-phase grounding, and interphase faults), due to the double-sequence coupling effect, the stator side voltage equation can be expressed as: U g is the grid voltage, K +is the positive sequence voltage equivalent coefficient, K − is the negative sequence voltage equivalent coefficient, Z e represents the equivalent sequence self-impedance, Z c Represents the equivalent sequence coupling impedance.

[0024] During an asymmetrical fault, overcurrent must be prevented and the RSC must be protected. Therefore, the rotor current constraint can be expressed as: x s represents the stator inductive reactance of the doubly fed wind turbine, x m represents the mutual inductive reactance of the doubly fed wind turbine, I rmax Indicates the upper limit of the rotor current.

[0025] To ensure the controllability of DFIG during faults, RSC must avoid overmodulation. Therefore, the rotor voltage constraint can be expressed as: s represents the slip rate of the doubly fed wind turbine, σ represents the magnetic leakage coefficient of the doubly fed wind turbine, U rmax Indicates the upper limit of the rotor voltage.

[0026] Under asymmetric faults, the DFIG should suppress the VUF to a predetermined range. Therefore, the VUF constraint can be expressed as: η Indicates the upper limit of voltage imbalance.

[0027] Based on the orientation angle obtained by DDSRF-PLL, the stator voltage equation can be further transformed through Park transformation: r e , x e Respectively Z e The real and imaginary parts of r c , x c Respectively Z c The real and imaginary parts of the positive and negative sequences are represented by S+(−), I sq+(−) Indicates positive and negative q Shaft current,I ' sd+(−) Indicates positive and negative sequence d Projection of the axis current, I ' sq+(−) Indicates positive and negative sequence q Projection of the shaft current.

[0028] The positive and negative sequence coupling terms need to be the projections on the original directional mode, expressed as: .

[0029] During the entire asymmetric fault period, the PLL should remain synchronized with the grid voltage, which means that the PLL must have a stable equilibrium point (SEP). S + >0 and S − >0 must be considered as a transient stability constraint expression since it is consistent with the existence of SEP.

[0030] As the optimization goal, the objective function is the output active power under asymmetric fault, which consists of positive sequence and negative sequence components and can be expressed as: Where max represents the maximum value, P s is the stator active power, U s+ is the stator positive sequence voltage, U s− is the stator negative sequence voltage, I sd+ Stator positive sequence d Shaft current, I sd− Stator negative sequence d Shaft current.

[0031] S2: Based on the optimal active power transmission capability improvement model, the positive sequence and negative sequence synchronous rotation coordinate systems are d The axes are unified to the grid voltage orientation mode and the dual-sequence synchronous rotating coordinate system is reconstructed to eliminate the nonlinearity and coupling characteristics caused by the dual-sequence power angle coupling term; Specifically, in order to eliminate the influence of coupling and nonlinear characteristics related to the power angle coupling term, considering that the grid voltage source is the source of the equivalent positive-sequence and negative-sequence sources in the circuit model, the d-axis of the positive-sequence and negative-sequence synchronous coordinate systems is oriented to the grid voltage. Figure 3 The schematic diagram of the reconstruction of the dual-sequence coordinate system of the DFIG wind turbine is shown in Figure 2. The voltage equation in the reconstructed dual-sequence synchronous coordinate system can be expressed as: U sd+ Indicates stator positive d Shaft voltage, U sd− Indicates stator load d Shaft voltage, U sq+ Indicates stator positive sequence q Shaft voltage; U sq− Indicates stator negative sequence q Shaft voltage; K 1+ , K 2+ Respectively K + The real and imaginary parts of K 1− , K 2− Respectively K − The real and imaginary parts of , ^ represent the state components in the reconstructed double-order coordinate system.

[0032] After the dual-sequence synchronous coordinate system is reconstructed, the transient stability constraint is naturally included in the above equation. Since the reconstruction process is merely an equivalent mathematical transformation, the solvability of the reconstruction equation establishes the existence of a stable equilibrium point for the dual-sequence PLL. As long as there is a feasible solution to the optimal APTC enhancement problem, it must satisfy S + >0 and S − >0, thus ensuring that the PLL has a stable equilibrium point.

[0033] S3: Based on the electrical quantities after the dual-sequence synchronous rotation coordinate system, a second-order cone relaxation transformation is performed on the rotor current constraint and the rotor voltage constraint, and a semi-positive definite relaxation transformation is performed on the voltage imbalance constraint. An augmented matrix variable is constructed and a rank constraint is introduced to form a standard semi-positive definite programming problem; Specifically, the stator voltage equation in the reconstructed double-sequence synchronous coordinate system can be expressed in matrix form: u = Zi + k u represents the stator voltage matrix, i represents the stator current matrix, k Represents the grid voltage matrix.

[0034] In order to eliminate the non-convexity of the rotor current constraint, based on the Cauchy inequality, the rotor current constraint can be further relaxed into a second-order cone form as follows: ZI represents the impedance matrix in the rotor current constraint, Q represents the auxiliary matrix of stator-rotor transformation.

[0035] Since this form is a standard second-order cone form, the convexity of the rotor current constraint is guaranteed. Similarly, the rotor voltage constraint can also be converted to a second-order cone form as follows: Z V represents the impedance matrix in the rotor voltage constraint, G represents the rotor voltage auxiliary matrix.

[0036] For the VUF constraint, it cannot be directly converted to a convex constraint, so a semi-positive definite relaxation is considered. The semi-positive definite augmented matrix variable Y is constructed as follows: Y Variables representing semidefinite programming problems.

[0037] Therefore, the semi-positive definite matrix form of the VUF constraint can be expressed as: tr represents the trace of the matrix, D represents the voltage unbalance auxiliary matrix, A c Represents the voltage unbalance coefficient matrix.

[0038] The linear terms in the objective function are eliminated and can be expressed as: obj The objective function of the optimization problem ，A obj Represents the objective function coefficient matrix.

[0039] The convex semidefinite programming problem is expressed as follows: in Y 5,5 express Y The element in the 5th row and 5th column of the matrix, rank Represents the rank of the matrix.

[0040] Note that for the second-order cone constraints (rotor current and rotor voltage constraints), there is no slack gap. However, for the VUF constraint, an auxiliary rank constraint, rank(Y)=1, must be introduced. Aside from the rank constraint, the original non-convex problem is transformed into a semidefinite programming problem that can be solved using commercial solvers. When the rank constraint holds, the entire problem has no slack gap. If the rank constraint does not hold, the original solution can still be approximated using established techniques such as eigenvalue decomposition or Gaussian randomization, often yielding highly accurate results.

[0041] S4: Based on the semi-positive definite programming model, according to the actual active power limit, adaptively coordinate the improvement of active power transmission capacity and the suppression of voltage imbalance, and iteratively adjust the limit value of the voltage imbalance constraint until the calculated active power is less than or equal to the actual active power limit.

[0042] Specifically, under actual operating conditions, active power may be limited by actual wind speed. When active power limits are insufficient, in addition to providing active power support, it is necessary to fully utilize the remaining available current capacity to attenuate VUF. Therefore, the feasibility of coordinating APTC enhancement and VUF attenuation must be analyzed.

[0043] Reference Figure 4 , which describes the geometric relationship between APTC enhancement and VUF decay. Figure 4 (a) shows the relationship between active power and VUF with respect to the rotor current phase angle φ when the rotor negative sequence current is determined. - . For regions II and IV, the VUF constraint is not tight because active power increases when VUF decreases, meaning the optimal solution is not in these two regions. Since both the output active power and the reduced VUF performance in region I are inferior to those in region III, the optimal solution should be in region III. More precisely, when the VUF constraint bound holds, the optimal solution is at point d. Figure 4 (b) shows the relationship between active power and VUF with respect to the negative sequence rotor current amplitude when the current constraint bound holds. The VUF constraint is a tight constraint on the optimal APTC enhancement objective because the reduction of VUF and the increase of active power constrain each other.

[0044] Reference Figure 5 , is the algorithm flow chart of the method of the present invention. When the calculated active power P cal Greater than the actual active power limit P max When VUF limit value η Decrease until P cal ≤ P max The iteration step size is set to: α n is the iteration step length, μ is the initial compensation coefficient, P cal0 is the initial calculated active power value, P max is the maximum power limit value, is the compensation iteration constant.

[0045] The iteration step size is controllable, as a larger initial step size can speed up convergence, while a smaller step size in the later stages can ensure the quality of the final solution.

[0046] As can be seen from the above embodiments, this application establishes an optimal active power transmission capacity improvement model that includes rotor current, rotor voltage, voltage imbalance, and transient stability constraints. The non-convex model is then convexified by techniques such as reconstructing a dual-order coordinate system and semi-positive relaxation to ensure the global optimality of the solution. Finally, active power transmission improvement and voltage imbalance suppression are adaptively coordinated based on actual power constraints. This invention can fully utilize the power and current capacity of a doubly-fed wind turbine generator system, significantly improving the active power output capacity under asymmetric faults while ensuring safe and stable operation, and effectively suppressing voltage imbalance.

[0047] Corresponding to the aforementioned embodiment of the method for improving the active power transmission capability of a wind turbine generator set under an asymmetric fault, the present application also provides an embodiment of a device for improving the active power transmission capability of a wind turbine generator set under an asymmetric fault.

[0048] Figure 6 This is a block diagram of a device for improving the active power transmission capability of a wind turbine generator set under an asymmetric fault according to an exemplary embodiment. Figure 6 , the device comprises: Model building module 1, for establishing an optimal active power transmission capability improvement model for a doubly-fed wind turbine generator system under asymmetric faults, wherein the model includes an objective function, rotor current constraints, rotor voltage constraints, voltage imbalance constraints, and transient stability constraints; The first convex processing module 2 is used to synchronously rotate the positive sequence and negative sequence coordinate systems based on the optimal active power transmission capability improvement model. d The axes are unified to the grid voltage orientation mode and the dual-sequence synchronous rotating coordinate system is reconstructed to eliminate the nonlinearity and coupling characteristics caused by the dual-sequence power angle coupling term; A second convexification processing module 3 is configured to perform a second-order cone relaxation transformation on the rotor current constraint and the rotor voltage constraint based on the electrical quantities after the dual-order synchronous rotation coordinate system, perform a semi-positive definite relaxation transformation on the voltage imbalance constraint, construct an augmented matrix variable and introduce a rank constraint to form a standard semi-positive definite programming problem; The adaptive solution module 4 is used to adaptively coordinate the improvement of active power transmission capacity and the suppression of voltage imbalance based on the semi-definite programming model and the actual active power limit, and iteratively adjust the limit value of the voltage imbalance constraint until the calculated active power is less than or equal to the actual active power limit.

[0049] Regarding the apparatus in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated here.

[0050] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to the partial description of the method embodiments. The device embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present application scheme. A person of ordinary skill in the art can understand and implement it without paying any creative work.

[0051] Correspondingly, the present application also provides an electronic device, comprising: one or more processors; a memory for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the method for improving the active power transmission capacity of a wind turbine under an asymmetric fault as described above.

[0052] Accordingly, the present application also provides a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implement the above-mentioned method for improving the active power transmission capability of a wind turbine generator set under an asymmetric fault.

[0053] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the contents disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of the present application and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered merely as exemplary, and the true scope and spirit of the present application are indicated by the claims.

[0054] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A method for improving the active power transmission capability of a wind turbine under asymmetric fault conditions, characterized in that: include: Establishing an optimal active power transmission capability improvement model for a doubly-fed wind turbine generator system under asymmetric faults, the model includes an objective function, rotor current constraints, rotor voltage constraints, voltage imbalance constraints, and transient stability constraints; Based on the optimal active power transmission capacity improvement model, the positive sequence and negative sequence synchronous rotation coordinate systems are d The axes are unified to the grid voltage orientation mode and the dual-sequence synchronous rotating coordinate system is reconstructed to eliminate the nonlinearity and coupling characteristics caused by the dual-sequence power angle coupling term; Based on the electrical quantities after the dual-sequence synchronous rotation coordinate system, a second-order cone relaxation transformation is performed on the rotor current constraint and the rotor voltage constraint, a semi-positive definite relaxation transformation is performed on the voltage imbalance constraint, an augmented matrix variable is constructed and a rank constraint is introduced to form a standard semi-positive definite programming problem; Based on the semi-positive definite programming model, according to the actual active power limit, the active power transmission capacity improvement and voltage imbalance suppression are adaptively coordinated, and the limit value of the voltage imbalance constraint is iteratively adjusted until the calculated active power is less than or equal to the actual active power limit.

2. The method according to claim 1, wherein: The objective function is expressed as follows: ； Where max represents the maximum value, P s is the stator active power, U s+ is the stator positive sequence voltage, U s− is the stator negative sequence voltage, I sd+ Stator positive sequence d Shaft current, I sd− Stator negative sequence d Shaft current; Among them, the stator positive and negative sequence voltages are expressed as follows: ； U g is the grid voltage, K + is the positive sequence voltage equivalent coefficient, K − is the negative sequence voltage equivalent coefficient, Z e represents the equivalent sequence self-impedance, Z c represents the equivalent sequence coupling impedance; Under the dual-sequence phase-locked loop orientation, the form after Park transformation is as follows: ； ； r e , x e Respectively Z e The real and imaginary parts of r c , x c Respectively Z c The real and imaginary parts of S+(−) represent the transient stability coefficients corresponding to the positive and negative sequences. I sq+(−) Indicates stator positive and negative q Shaft current, I ' sd+(−) Indicates the positive and negative sequence of the stator d Projection of the axis current, I ' sq+(−) Indicates the positive and negative sequence of the stator q Projection of the shaft current.

3. The method according to claim 1, wherein: The rotor current constraint is expressed as follows: ； x s represents the stator inductive reactance of the doubly fed wind turbine, x m represents the mutual inductive reactance of the doubly fed wind turbine, I rmax Indicates the upper limit of the rotor current; The rotor voltage constraint is expressed as follows: ； s represents the slip rate of the doubly fed wind turbine, σ represents the leakage flux coefficient of the doubly fed wind turbine, U rmax Indicates the upper limit of the rotor voltage; The voltage imbalance constraint is expressed as follows: ； η Indicates the upper limit of voltage imbalance.

4. The method according to claim 1, wherein: The stator voltage equation in the reconstructed dual-sequence synchronous coordinate system is expressed as: ； U sd+ Indicates stator positive d Shaft voltage, U sd− Indicates stator load d Shaft voltage, U sq+ Indicates stator positive sequence q Shaft voltage; U sq− Indicates stator negative sequence q Shaft voltage; K 1+ , K 2+ Respectively K + The real and imaginary parts of K 1− , K 2− Respectively K − The real and imaginary parts of , ^ represents the state component in the reconstructed double-order coordinate system.

5. The method according to claim 1, wherein: The stator voltage equation in the reconstructed double-sequence synchronous coordinate system is expressed in matrix form: u = Zi + k； u represents the stator voltage matrix, i represents the stator current matrix, k represents the grid voltage matrix; The rotor current constraint is relaxed by a second-order cone based on the Cauchy inequality, which is expressed as follows: ； Z I represents the impedance matrix in the rotor current constraint, Q represents the auxiliary matrix of stator-rotor transformation; Similarly, the rotor voltage constraint is subjected to second-order cone relaxation, which is expressed as follows: ； Z V represents the impedance matrix in the rotor voltage constraint, G represents the rotor voltage auxiliary matrix; Create a positive semidefinite matrix variable, represented as follows: ； Y Variables representing semidefinite programming problems; The voltage imbalance constraint is subjected to a semi-positive definite relaxation transformation, which is expressed as follows: ； tr Represents the trace of a matrix ，D represents the voltage unbalance auxiliary matrix, A c represents the voltage unbalance coefficient matrix; The linear terms in the objective function are eliminated and expressed as: ； obj The objective function of the optimization problem ，A obj Represents the objective function coefficient matrix.

6. The method according to claim 5, characterized in that: The solution to the semi-positive programming problem is expressed as follows: ； in Y 5,5 express Y The element in the 5th row and 5th column of the matrix, rank Represents the rank of the matrix.

7. The method according to claim 1, wherein: The voltage unbalance limit value η The iteration step size is set to: ； α n is the iteration step length, μ is the initial compensation coefficient, P cal0 is the initial calculated active power value, P max is the maximum power limit value.

8. A device for improving the active power transmission capability of a wind turbine under asymmetric fault conditions, characterized in that: include: A model building module is used to establish an optimal active power transmission capability improvement model for a doubly-fed wind turbine generator system under asymmetric faults, wherein the model includes an objective function, rotor current constraints, rotor voltage constraints, voltage imbalance constraints, and transient stability constraints; The first convex processing module is used to synchronously rotate the positive sequence and negative sequence coordinate systems based on the optimal active power transmission capability improvement model. d The axes are unified to the grid voltage orientation mode and the dual-sequence synchronous rotating coordinate system is reconstructed to eliminate the nonlinearity and coupling characteristics caused by the dual-sequence power angle coupling term; A second convexification processing module is configured to perform a second-order cone relaxation transformation on the rotor current constraint and the rotor voltage constraint based on the electrical quantities after the dual-order synchronous rotation coordinate system, perform a semi-positive definite relaxation transformation on the voltage imbalance constraint, construct an augmented matrix variable, and introduce a rank constraint to form a standard semi-positive definite programming problem; An adaptive solution module is used to adaptively coordinate the improvement of active power transmission capability and the suppression of voltage imbalance based on the semi-definite programming model and the actual active power limit, and iteratively adjust the limit value of the voltage imbalance constraint until the calculated active power is less than or equal to the actual active power limit.

9. An electronic device, characterized in that: include: one or more processors; a memory for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having computer instructions stored thereon, characterized in that: When the instruction is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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