A low-voltage ride-through transient stability improvement method and device for grid-connected converters based on TS fuzzy model and attraction domain estimation, and a medium

Abstract

This invention discloses a method, device, and medium for improving the transient stability of a grid-connected converter during low-voltage ride-through (LVRT) based on a TS fuzzy model and attraction domain estimation. It belongs to the fields of power electronics technology and fault ride-through technology for new energy power generation systems. The method includes: using a logarithmic-exponential composite function to handle the non-differentiable characteristics of LVRT limiting control and establishing a full-order nonlinear differential-algebraic model; estimating the attraction domain of the grid-connected converter system based on the TS fuzzy model and linear matrix inequality method; and analyzing the influence of control parameters on transient stability. The beneficial effects of this invention are: constructing a Lyapunov function based on the TS fuzzy model and LMI method; quantitatively estimating the attraction domain of the grid-connected converter system; and analyzing the influence of parameters on transient stability. Simulations and experiments show that the grid-connected converter maintains transient stability when the initial LVRT switching point is within the attraction domain; and optimizing control parameters can improve the transient stability margin during the switching process.

Description

Technical Field

[0001] This invention relates to the fields of power electronics technology and fault ride-through technology of new energy power generation systems, specifically to a method, device and medium for improving the transient stability of low voltage ride-through of grid-connected converters based on TS fuzzy model and attraction domain estimation. Background Technology

[0002] In recent years, renewable energy generation, represented by photovoltaic and wind power, has been largely connected to the grid through grid-following converters. Under grid voltage dips caused by faults, to ensure the reliability of renewable energy generation, grid-following converters (GFLCs) need to undergo low-voltage grid connection tests according to the low-voltage ride-through (LVRT) standard. This requires not only rapid restoration of synchronization with the grid but also the provision of a certain amount of reactive current to support the grid voltage.

[0003] However, as grid strength weakens, the increased equivalent reactance of the grid converter leads to potentially severe voltage fluctuations during large disturbances. These voltage fluctuations can cause not only phase-locked loop (PLL) loss of lockout but also interactive instability issues between LVRT control and the grid. This means that even GFLCs that have passed the grid specification low-voltage test may still face instability risks during actual LVRT, potentially even leading to the disconnection of renewable energy units from the grid.

[0004] For the stability analysis of GFLCs considering LVRT control, existing studies have not considered the piecewise nondifferentiability of the nonlinear model caused by LVRT limiting control and its impact on transient stability analysis. In particular, when the operating point of the grid-connected converter system spans different control modes, the traditional Lyapunov function (LF) construction method often fails due to model nondifferentiability, severely limiting the application of existing LF methods in practical systems. Constructing the attraction domain of a high-order nonlinear system considering LVRT limiting and analyzing the impact of circuit and control parameters on the transient stability of the grid-connected converter system are particularly important. Therefore, it is urgent to construct a differentiable nonlinear system while ensuring model accuracy, to quantize the attraction domain and optimize parameters, providing a simple and feasible method to improve the transient stability of GFLCs crossing grid voltage sags under weak grid conditions. Summary of the Invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] Therefore, the technical problem solved by this invention is: addressing the issue that the model of a grid-following converter (GFLC) becomes piecewise nondifferentiable and traditional Lyapunov function construction methods fail during low voltage ride-through (LVRT) in weak grid conditions due to amplitude limiting control. This invention provides a nonlinear system construction method that ensures model accuracy and differentiability, enabling accurate quantification of the attraction domain of high-order nonlinear systems considering LVRT amplitude limiting control, and analyzing the impact of circuit and control parameters on transient stability. This optimizes the grid-following converter system parameters, improves the transient stability of the GFLC under grid voltage sag conditions, and prevents unit disconnection from the grid.

[0007] To address the aforementioned technical problems, this invention provides the following technical solution: a method for improving the low-voltage ride-through transient stability of a grid-type converter based on a TS fuzzy model and attraction domain estimation, comprising, A logarithmic-exponential composite function is used to handle the non-differentiable characteristics of low-voltage ride-through limiting control, and a full-order nonlinear differential equation model considering low-voltage ride-through limiting control is established. The attraction domain is characterized by the TS fuzzy model and linear matrix inequalities. The influence of control parameters on the transient stability of the grid-connected converter is analyzed by estimating the attraction domain. Based on the analysis of the influence of control parameters on the transient stability of the grid-connected converter, the transient stability of the low-voltage ride-through switching process of the grid-connected converter is improved by optimizing the control parameters to expand the attraction domain.

[0008] As a preferred embodiment of the low-voltage ride-through transient stability improvement method for a grid-type converter based on the TS fuzzy model and attraction domain estimation described in this invention, the establishment of the full-order nonlinear differential equation model considering low-voltage ride-through limiting control includes establishing mathematical models of low-voltage ride-through control, phase-locked loop, current loop, and main circuit respectively.

[0009] The mathematical model for establishing low-voltage ride-through control includes the following: when a large disturbance causes the grid-connected converter to enter low-voltage ride-through mode, the fluctuation of the terminal voltage will cause the reactive current control to switch between saturation and desaturation. Follow Dynamic changes: in, This is expressed as a reference value for reactive current. This is a reference value for the reactive current of the grid-type converter in normal mode. Represented as terminal voltage, This represents the reference value for the voltage of the grid converter system. This represents the reference value for the current in the grid converter system. This is the current limiting value. This represents the q-axis current gain for typical reactive current control. Current limiting factor; This is expressed as a reference value for active current. This is the reference value for the active current of the grid-type converter in normal mode.

[0010] As a preferred embodiment of the low-voltage ride-through transient stability improvement method for a grid-type converter based on the TS fuzzy model and attraction domain estimation described in this invention, the mathematical model of the phase-locked loop is expressed as follows: in, This is the generation term of the integrator in phase-locked loop PI control. To track the q-axis component of the voltage at PCC in the grid-type converter, Represented as The differential form, It is expressed as the phase angle difference between the grid-type converter and the power grid. Represented as Differential form, and These are the proportional and integral coefficients in the PI control of the PLL, respectively.

[0011] The mathematical model of the current loop is expressed as follows: in, Represented as The differential form, Represented as The differential form, , These represent the outputs of the integrator in the d-axis current loop PI control and the q-axis current loop PI control, respectively. This is expressed as a reference value for the inductor current on the d-axis. This is expressed as a reference value for the inductor current on the q-axis. This is expressed as the actual value of the inductor current on the d-axis. This is expressed as the actual value of the inductor current on the q-axis. , These are the proportional and integral coefficients of the current loop PI controller. To provide a reference value for the d-axis of the port voltage of the grid converter. This is the q-axis reference value for the port voltage of the grid converter. For filtering inductors, This represents the q-axis value of the PCC voltage.

[0012] The mathematical model of the main circuit is expressed as follows: in, Represented as The differential form, This is expressed as the actual value of the inductor current on the d-axis. This is the output of the integrator in the d-axis current loop PI control. , These are the proportional and integral coefficients of the current loop PI controller. and These are the proportional and integral coefficients in the PI control of the PLL, respectively. For filtering inductors, Represented as filter resistor, To track the q-axis component of the voltage at PCC in the grid-type converter, To match the d-axis value of the voltage at PCC in the grid-type converter, Represented as The differential form, This is expressed as the actual value of the inductor current on the q-axis. This is expressed as a reference value for the inductor current on the q-axis. This is the output of the integrator in the q-axis current loop PI control. Represented as The differential form, Represented as common capacitor, Represented as the grid angular frequency, This represents the grid-side inductor current at the d-axis common junction point PCC. Represented as The differential form, This represents the grid-side inductor current at the q-axis common junction point PCC. Represented as The differential form, Represented as grid-side line resistance, Represented as grid-side line inductance, Represented as grid voltage, It is expressed as the phase angle difference between the grid-type converter and the power grid. It is expressed as the cosine of the phase angle difference between the grid-connected converter and the power grid. Represented as The differential form, It is expressed as the sine value of the phase angle difference between the grid-type converter and the power grid.

[0013] As a preferred embodiment of the low-voltage ride-through transient stability improvement method for a grid-type converter based on the TS fuzzy model and attraction domain estimation described in this invention, the following is provided: A full-order nonlinear differential equation model is obtained based on the mathematical model of low-voltage ride-through control, the mathematical model of the phase-locked loop, the mathematical model of the current loop, and the mathematical model of the main circuit, expressed as follows: in, Represented as Differential form, This is the generation term of the integrator in phase-locked loop PI control. To track the q-axis component of the voltage at PCC in the grid-type converter, Represented as The differential form, It is expressed as the phase angle difference between the grid-type converter and the power grid. and These are the proportional and integral coefficients in the PI control of the PLL, respectively. Represented as The differential form, Represented as The differential form, , These represent the outputs of the integrator in the d-axis current loop PI control and the q-axis current loop PI control, respectively. This is expressed as a reference value for the inductor current on the d-axis. This is expressed as a reference value for the inductor current on the q-axis. This is expressed as the actual value of the inductor current on the d-axis. This is expressed as the actual value of the inductor current on the q-axis. Represented as The differential form, This is expressed as the actual value of the inductor current on the d-axis. This is the output of the integrator in the d-axis current loop PI control. This is expressed as a reference value for the inductor current on the d-axis. , These are the proportional and integral coefficients of the current loop PI controller. and These are the proportional and integral coefficients in the PI control of the PLL, respectively. This is expressed as the actual value of the inductor current on the q-axis. To match the d-axis value of the voltage at PCC in the grid-type converter, This is the generation term of the integrator in phase-locked loop PI control. For filtering inductors, Represented as filter resistor, Represented as The differential form, This is expressed as a reference value for the inductor current on the q-axis. This is the output of the integrator in the q-axis current loop PI control. To track the q-axis component of the voltage at PCC in the grid-type converter, Represented as The differential form, Represented as common capacitor, This represents the grid-side inductor current at the d-axis common junction point PCC. Represented as the grid angular frequency, Represented as The differential form, This represents the grid-side inductor current at the q-axis common junction point PCC. Represented as The differential form, Represented as grid-side line resistance, Represented as grid-side line inductance, Represented as grid voltage, It is expressed as the phase angle difference between the grid-type converter and the power grid. It is expressed as the cosine of the phase angle difference between the grid-connected converter and the power grid. Represented as The differential form, It is expressed as the sine value of the phase angle difference between the grid-type converter and the power grid.

[0014] As a preferred embodiment of the low-voltage ride-through transient stability improvement method for a grid-type converter based on a TS fuzzy model and attraction domain estimation described in this invention, wherein: the characterization and estimation of the attraction domain includes, Construct the Lyapunov function for the mesh converter system.

[0015] Initialize the state variables of the nonlinear term and .

[0016] Solve for the coefficient matrix.

[0017] Substituting the coefficient matrix into the linear matrix inequality, if the linear matrix inequality has a solution, then the constant matrix in the Lyapunov function of the grid converter system is obtained. Increase according to the iteration step size , reduce Then, the coefficient matrix is ​​solved.

[0018] If the linear matrix inequality has no solution, then a constant matrix M and state variables are used. and Describe and estimate the attraction domain.

[0019] As a preferred embodiment of the low-voltage ride-through transient stability improvement method for a grid-type converter based on a TS fuzzy model and attraction domain estimation described in this invention, wherein: the TS fuzzy model is expressed as follows: in, Represented as a TS fuzzy model, Represents the weighting function. Represented as a coefficient matrix, Represented as state variables, It is represented as an intermediate variable.

[0020] The linear matrix inequality is expressed as follows: in, It is represented as a constant matrix, and r represents the number of elements.

[0021] As a preferred embodiment of the low-voltage ride-through transient stability improvement method for a grid-type converter based on the TS fuzzy model and attraction domain estimation described in this invention, the analysis of the influence of control parameters on the transient stability of the grid-type converter system includes: The effects of phase-locked loop, current loop, and SCR parameters on the transient stability of a grid-connected converter during low-voltage ride-through are analyzed using the estimated attraction domain.

[0022] This invention provides a computer device, including a memory and a processor, wherein the memory stores a computer program, characterized in that the processor executes the computer program to implement the steps of the described method for improving the low-voltage ride-through transient stability of a grid-type converter based on a TS fuzzy model and attraction domain estimation.

[0023] The present invention provides a computer-readable storage medium having a computer program stored thereon, characterized in that, when the computer program is executed by a processor, it implements the steps of the method for improving the low-voltage ride-through transient stability of a grid-type converter based on a TS fuzzy model and attraction domain estimation.

[0024] The beneficial effects of this invention are as follows: This invention addresses the problem of transient instability in grid-connected converter systems caused by the drastic voltage fluctuations during the switching of a GFLC from normal control mode to LVRT mode under weak grid conditions, leading to frequent GFLC entry and exit from LVRT mode. This invention provides a method for improving the transient stability of grid-connected converters during low-voltage ride-through based on a TS fuzzy model and attraction domain estimation. It approximates the piecewise non-differentiable function introduced by LVRT control using a differentiable function, ensuring it meets the continuous differentiability condition required for conventional stability analysis. A full-order nonlinear differential equation including LVRT control, PLL, current loop, and main circuit components is established. The Lyapunov function of the grid-connected converter system is constructed using the TS fuzzy model and LMI method. The attraction domain of the grid-connected converter system is quantitatively estimated, and the influence of system parameters on transient stability is analyzed. Simulations and experiments verify that the grid-connected converter system can maintain transient stability when the initial point is located within the attraction domain of the equilibrium point during LVRT switching. Optimizing control parameters can improve the transient stability margin during LVRT switching. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0026] Figure 1 This invention provides a method for improving the transient stability of a grid-connected converter during low-voltage ride-through based on a TS fuzzy model and attraction domain estimation, including the circuit topology of the grid-connected converter, normal control of the grid-connected converter before and after voltage drop, and low-voltage ride-through control diagram.

[0027] Figure 2 The following is a flowchart of an overall method for improving the low-voltage ride-through transient stability of a grid-type converter based on a TS fuzzy model and attraction domain estimation, provided as an embodiment of the present invention.

[0028] Figure 3 The figure shows the simulation results of the LVRT process under different SCRs for a grid-type converter based on the TS fuzzy model and attraction domain estimation, which is an embodiment of the present invention.

[0029] Figure 4 This is a comparison chart of the limiter output value and the actual output value of a function of a grid-type converter low-voltage ride-through transient stability improvement method based on TS fuzzy model and attraction domain estimation, provided as an embodiment of the present invention.

[0030] Figure 5 The diagram shows the verification of the differential equation model for a low-voltage ride-through transient stability improvement method for a grid-type converter based on a TS fuzzy model and attraction domain estimation, as provided in an embodiment of the present invention.

[0031] Figure 6 This invention provides an estimated attraction domain diagram for different PLL parameters of a low-voltage ride-through transient stability improvement method for a grid-type converter based on a TS fuzzy model and attraction domain estimation, as an embodiment of the present invention.

[0032] Figure 7 This invention provides an estimated attraction domain diagram for different current loops in a low-voltage ride-through transient stability improvement method for a grid-type converter based on a TS fuzzy model and attraction domain estimation, as an embodiment of the present invention.

[0033] Figure 8 This invention provides an estimated attraction domain diagram for different SCRs of a low-voltage ride-through transient stability improvement method for a grid-type converter based on a TS fuzzy model and attraction domain estimation, as an embodiment of the present invention.

[0034] Figure 9 This is a time-domain simulation comparison of different kpplls of the LVRT process of a grid-type converter based on a TS fuzzy model and attraction domain estimation, provided as an embodiment of the present invention.

[0035] Figure 10 This is a time-domain simulation comparison of different kipll methods for improving the low voltage ride-through transient stability of a grid-type converter based on the TS fuzzy model and attraction domain estimation, provided as an embodiment of the present invention.

[0036] Figure 11 This is a time-domain simulation comparison of different kiacc methods for improving the low voltage ride-through transient stability of a grid-type converter based on the TS fuzzy model and attraction domain estimation, provided as an embodiment of the present invention.

[0037] Figure 12 This is a time-domain simulation comparison of different kpacc of the LVRT process for a grid-type converter based on the TS fuzzy model and attraction domain estimation, as provided in an embodiment of the present invention.

[0038] Figure 13 This invention provides a comparison of EDA and phase trajectory diagrams under different SCRs for a low-voltage ride-through transient stability improvement method for a grid-type converter based on a TS fuzzy model and attraction domain estimation, as an embodiment of the present invention.

[0039] Figure 14 The waveforms of experimental cases 1 and 2 are provided for an embodiment of the present invention, which is a method for improving the low voltage ride-through transient stability of a grid-type converter based on the TS fuzzy model and attraction domain estimation. Detailed Implementation

[0040] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0041] Example 1, referring to Figures 1-8 This is one embodiment of the present invention, which provides a method for improving the low-voltage ride-through transient stability of a grid-type converter based on a TS fuzzy model and attraction domain estimation, including: like Figure 1The diagram illustrates the circuit topology of a grid-following converter (GFLC), its normal control before and after voltage sags, and its low-voltage ride-through (LVRT) control. The DC-side voltage of the GFLC is shown below. The AC side is filtered by an LC filter and the grid-side line impedance. and It is connected to the power grid. Normal control consists of a power loop, a current loop, and a phase-locked loop (PLL). When a fault causes a voltage dip in the grid, the GFLC switches to LVRT control. At this time, the power loop fails, and only the PLL and current loop remain operational.

[0042] LVRT control employs a reactive current priority control method to support the terminal voltage. Under normal control, the terminal voltage >0.9 , and Generated by the power loop, at which point the switch... Close. When a severe voltage drop occurs in the mains power grid, the terminal voltage is detected; if the terminal voltage... <0.9 At this time, the GFLC switches to LVRT control, and the switch... closure, and According to the terminal voltage It is calculated using formula (1).

[0043] (1) in, This is expressed as a reference value for active current. This is expressed as a reference value for reactive current. Represented as terminal voltage, and These are the active current reference value and reactive current reference value of the grid-type converter in normal mode, respectively. This represents the reference value for the voltage of the grid converter system. This represents the reference value for the current in the grid converter system. This is the current limiting value. For typical reactive current control, q-axis current gain is denoted as min.

[0044] To visually demonstrate the transient instability of a grid-connected converter system switching from normal mode to LVRT mode under different grid strengths, a system was built in Matlab / Simulink as follows: Figure 1 The simulation model is shown, and the simulation parameters are listed in Table 1. SCR is considered an indicator of grid strength; it is proposed that when SCR is less than 2, the grid-connected converter system is considered a weak grid. The simulation conditions are set as follows: before time t=1s, the grid-connected converter system operates in normal mode, and the grid voltage... Terminal voltage and active current and reactive current All are rated values. When t=1s, The voltage dropped to 0.65 PU, and the grid converter system switched from normal mode to LVRT mode. Figure 3 Simulation results of LVRT process under different SCRs, The voltage at the two phase terminals ab Table 1 System parameters of the grid converter

[0045] In Table 1, and The instruction values ​​are represented as active and reactive power. and They are q The proportional and integral coefficients of the shaft power loop PI controller Represented as common capacitor, Represented as the grid angular frequency, Represented as filter resistor, Represented as grid voltage, Represented as grid-side line resistance, , These are the proportional and integral coefficients of the current loop PI controller. and These are the proportional and integral coefficients in the PI control of the PLL, respectively. This represents the q-axis current gain under typical reactive current control.

[0046] Simulation results are as follows Figure 3 (a) and Figure 3 As shown in (b). Figure 3 (a) Relatively strong grid conditions corresponding to SCR=2.9 Figure 3 (b) Relatively weak grid conditions with SCR=2. At SCR=2.9, , and All converged to a new steady state, indicating that the grid converter system can stably achieve LVRT. However, when SCR=2, Oscillation occurs. and The presence of amplitude-limited oscillations indicates that transient instability has occurred during the LVRT process. Figure 3 As shown in (b), at the terminal voltage During the oscillation, when When the voltage rises sharply and exceeds 0.9UB (LVRT trigger signal), the mesh converter system exits LVRT mode, and then... It also rose sharply, which in turn led to It plummeted to below 0.9 The grid-connected converter system repeatedly enters and exits LVRT mode. This frequent entry and exit of LVRT mode not only damages the grid-connected converter system but also reduces its transient stability. Simulation results show that under weak grid conditions, the grid-connected converter system exhibits transient instability during LVRT.

[0047] To address the aforementioned transient instability, the present invention employs the following technical solution: S1: The non-differentiable characteristics of low-voltage ride-through limiting control are handled by using a logarithmic-exponential composite function, and a full-order nonlinear differential equation model considering low-voltage ride-through limiting control is established.

[0048] The establishment of a full-order nonlinear differential equation model considering low-voltage ride-through limiting control includes establishing mathematical models of low-voltage ride-through control, phase-locked loop, current loop, and main circuit. When a large disturbance causes the grid-connected converter system to enter LVRT mode, the fluctuation of the terminal voltage will cause the reactive current control to switch between saturation and desaturation. At this time, will follow Dynamic changes, formula (1) can be expressed as: (2) in, This is expressed as a reference value for active current. This is expressed as a reference value for reactive current. Represented as terminal voltage, and These are the active current reference value and reactive current reference value of the grid-type converter in normal mode, respectively. This represents the reference value for the voltage of the grid converter system. This represents the reference value for the current in the grid converter system. This is the current limiting value. This represents the q-axis current gain for typical reactive current control. Current limiting coefficient.

[0049] In formula (2), The piecewise nature of the structure introduces a non-differentiable point into the grid converter system, i.e. exist =0.9 A point where the left derivative is 1 and the right derivative is 0, and the left derivative is not equal to the right derivative, indicates a point that is not differentiable. =(0.9- / k) Similarly, points are also non-differentiable. However, this non-differentiability contradicts the continuous differentiability condition required by conventional stability analysis, leading to theoretical obstacles in stability analysis.

[0050] In the field of power system state estimation, a piecewise function is approximated by constructing a composite differentiable function based on a logarithmic-exponential function, expressed as: (3) Among them, the fitting coefficient A sufficiently large value needs to be selected to ensure approximation accuracy. This article Taking 30 yields better results. This is represented as the minimum output value. This represents the minimum input value. This represents the maximum input value. For typical reactive current control q Axis current gain.

[0051] Therefore, in formula (2) The piecewise function can be approximated as a smooth function that is differentiable everywhere: (4) in, This is expressed as a reference value for reactive current. This is a reference value for the reactive current of the grid-type converter in normal mode. This represents the reference value for the voltage of the grid converter system. This represents the reference value for the current in the grid converter system. This is the current limiting value. This represents the q-axis current gain for typical reactive current control. This is represented by dynamic voltage changes.

[0052] The rationale for using formula (4) instead of formula (2) is as follows: 1) When <(0.9- / k) At that time, due to Much greater than 1, (-k(0.9- / ) + )and (-k(0.9- / ) - The exponential term is much less than 0. and Much less than 1, and thus and ≈0. Therefore ≈- .

[0053] 2) When >0.9 At that time, due to Much greater than 1, and Much greater than 0, exponential term and Much greater than 1, and thus ≈ = Similarly, ≈ Therefore .

[0054] 3) When (0.9- / k) ≤ ≤0.9 Then, a similar derivation can be obtained. ≈ (-k(0.9- / ) + ), ≈0, therefore ≈-k(0.9- / ) .

[0055] Comparing the function output value of formula (4) before and after fitting with the actual output value of formula (2), the results are as follows: Figure 4 As shown. By Figure 4 It can be seen that there is a slight deviation between the function output value and the actual value at the inflection point, and the goodness of fit is high, which proves the feasibility of using a differentiable function to approximate the piecewise expression.

[0056] The mathematical model of a phase-locked loop is expressed as follows: (5) in, This is the generation term of the integrator in phase-locked loop PI control. To track the q-axis component of the voltage at PCC in the grid-type converter, Represented as The differential form, It is expressed as the phase angle difference between the grid-type converter and the power grid. Represented as Differential form, and These are the proportional and integral coefficients in the PI control of the PLL, respectively.

[0057] Proportional and integral coefficients in PI control: (6) (7) in, Represented as The differential form, Represented as The differential form, , These represent the outputs of the integrator in the d-axis current loop PI control and the q-axis current loop PI control, respectively. This is expressed as a reference value for the inductor current on the d-axis. This is expressed as a reference value for the inductor current on the q-axis. This is expressed as the actual value of the inductor current on the d-axis. This is expressed as the actual value of the inductor current on the q-axis. , These are the proportional and integral coefficients of the current loop PI controller. To provide a reference value for the d-axis of the port voltage of the grid converter. This is the q-axis reference value for the port voltage of the grid converter. For filtering inductors, This represents the q-axis value of the PCC voltage.

[0058] The mathematical model of the main circuit is expressed as follows: (8) in, Represented as The differential form, This is expressed as the actual value of the inductor current on the d-axis. This is the output of the integrator in the d-axis current loop PI control. , These are the proportional and integral coefficients of the current loop PI controller. and These are the proportional and integral coefficients in the PI control of the PLL, respectively. For filtering inductors, Represented as filter resistor, To track the q-axis component of the voltage at PCC in the grid-type converter, To match the d-axis value of the voltage at PCC in the grid-type converter, Represented as The differential form, This is expressed as the actual value of the inductor current on the q-axis. This is expressed as a reference value for the inductor current on the q-axis. This is the output of the integrator in the q-axis current loop PI control. Represented as The differential form, Represented as common capacitor, Represented as the grid angular frequency, This represents the grid-side inductor current at the d-axis common junction point PCC. Represented as The differential form, This represents the grid-side inductor current at the q-axis common junction point PCC. Represented as The differential form, Represented as grid-side line resistance, Represented as grid-side line inductance, Represented as grid voltage, It is expressed as the phase angle difference between the grid-type converter and the power grid. It is expressed as the cosine of the phase angle difference between the grid-connected converter and the power grid. Represented as The differential form, It is expressed as the sine value of the phase angle difference between the grid-type converter and the power grid.

[0059] Based on the mathematical models of low-voltage ride-through control, phase-locked loop, current loop, and main circuit, a full-order nonlinear differential equation model is obtained, expressed as follows: (9) in, Represented as Differential form, This is the generation term of the integrator in phase-locked loop PI control. To track the q-axis component of the voltage at PCC in the grid-type converter, Represented as The differential form, It is expressed as the phase angle difference between the grid-type converter and the power grid. and These are the proportional and integral coefficients in the PI control of the PLL, respectively. Represented as The differential form, Represented as The differential form, , These represent the outputs of the integrator in the d-axis current loop PI control and the q-axis current loop PI control, respectively. This is expressed as a reference value for the inductor current on the d-axis. This is expressed as a reference value for the inductor current on the q-axis. This is expressed as the actual value of the inductor current on the d-axis. This is expressed as the actual value of the inductor current on the q-axis. Represented as The differential form, This is expressed as the actual value of the inductor current on the d-axis. This is the output of the integrator in the d-axis current loop PI control. This is expressed as a reference value for the inductor current on the d-axis. , These are the proportional and integral coefficients of the current loop PI controller. and These are the proportional and integral coefficients in the PI control of the PLL, respectively. This is expressed as the actual value of the inductor current on the q-axis. To match the d-axis value of the voltage at PCC in the grid-type converter, This is the generation term of the integrator in phase-locked loop PI control. For filtering inductors, Represented as filter resistor, Represented as The differential form, This is expressed as a reference value for the inductor current on the q-axis. This is the output of the integrator in the q-axis current loop PI control. To track the q-axis component of the voltage at PCC in the grid-type converter, Represented as The differential form, Represented as common capacitor, This represents the grid-side inductor current at the d-axis common junction point PCC. Represented as the grid angular frequency, Represented as The differential form, This represents the grid-side inductor current at the q-axis common junction point PCC. Represented as The differential form, Represented as grid-side line resistance, Represented as grid-side line inductance, Represented as grid voltage, It is expressed as the phase angle difference between the grid-type converter and the power grid. It is expressed as the cosine of the phase angle difference between the grid-connected converter and the power grid. Represented as The differential form, It is expressed as the sine value of the phase angle difference between the grid-type converter and the power grid.

[0060] To verify the correctness of the model, a system was built in MATLAB / Simulink as follows: Figure 1 The model is shown, and the simulation parameters are shown in Table 1. The established nonlinear model is verified through a large disturbance condition, and the solution of the nonlinear model is compared with the time-domain simulation waveform. The large disturbance condition is set as follows: the grid voltage drops to 0.7 pu at 1s and to 0.65 pu at 1.5s. The dynamic response curves of various variables of the grid converter system are shown in Figure 5, including the dq axis PCC voltage of the GFLC. dq axis inductor current Harmony and angle The results show that the curves of the nonlinear model and the simulation model highly overlap after a large disturbance, verifying the correctness of the nonlinear model established in this paper.

[0061] S2: The attraction region is estimated using the TS fuzzy model and linear matrix inequalities.

[0062] To evaluate whether the net-type converter system can stably achieve LVRT under large disturbances, this section first constructs the Lyapunov function (LF) of the net-type converter system and uses the LF to characterize the estimated domain of attraction (EDA), and then analyzes the impact of parameter changes on transient stability. The specific steps for constructing the LF and the domain of attraction of the net-type converter system are as follows: For the nonlinear model formula (9) established in this paper, the equilibrium point of the grid converter system is moved to the origin of the coordinate system through coordinate transformation, and the state variables... - The coordinate transformation formula is as follows: (10) in, Let the state variable be 1. This is the generation term of the integrator in phase-locked loop PI control. This refers to the steady-state integral term generated by the integrator in phase-locked loop PI control. For state variable 2, It is expressed as the phase angle difference between the grid-type converter and the power grid. It is expressed as the steady-state value of the phase angle difference between the grid-connected converter and the power grid; For state variable 3, These are the outputs of the integrator in the d-axis current loop PI control. These are the steady-state output values ​​of the integrator in the d-axis current loop PI control; State variable 4, These are the outputs of the integrator in the q-axis current loop PI control. These are the steady-state output values ​​of the integrator in the q-axis current loop PI control; State variable 5, This is expressed as the actual value of the inductor current on the d-axis. This is expressed as the actual value of the inductor current on the d-axis under steady-state conditions. State variable 6, This is expressed as the actual value of the inductor current on the q-axis. This is expressed as the actual value of the inductor current on the q-axis under steady-state conditions. State variable 7, This represents the grid-side inductor current at the d-axis common junction point PCC. This represents the steady-state value of the grid-side inductor current at the d-axis common connection point PCC; State variable 8, This represents the grid-side inductor current at the q-axis common junction point PCC. This represents the steady-state value of the grid-side inductor current at the q-axis common connection point PCC; State variable 9, To track the d-axis component of the voltage at the PCC of the grid-type converter, This refers to the steady-state value of the d-axis component of the voltage at the PCC in the grid-type converter. State variable 10, To track the q-axis component of the voltage at PCC in the grid-type converter, This refers to the steady-state value of the q-axis component of the voltage at the PCC in the grid-type converter.

[0063] The nonlinear model formula (9) of the grid converter system is expressed as follows: Form, among which, This is a nonlinear matrix, where x represents the state variables, as detailed in formula (12). It contains 3 nonlinear terms , and ,in, - The state variables corresponding to the nonlinear terms are shown in formulas (13) and (14). Given the state variables corresponding to each nonlinear term... Extreme values ​​of (i=1, 6, 10) and The extreme values ​​of nonlinear terms can be determined. and The input space is divided using nonlinear terms. Each subspace contains a fuzzy subspace, within which a locally linear model of the original nonlinear system is established. For example, the first extreme value combination is... The corresponding local linear model is = ( ) Among them, ( Substituting into formula (9), we can obtain ( The value of ) can be obtained similarly for the other local models.

[0064] Based on this, according to the nonlinear term right and The membership degree of (i=1, 6, 10) is used to assign a weight function to each local linear model. (i=1,2,…, ), with the weight function of the first local linear model For example, as shown in formula (11), other weights can be obtained similarly: (11) in, For the weight function, This is the nonlinear term corresponding to state variable 1. This is the nonlinear term corresponding to state variable 6. This is the nonlinear term corresponding to state variable 10. The membership degree corresponding to state variable 1. The membership degree corresponding to state variable 6. This represents the membership degree corresponding to state variable 10.

[0065] (12) in, This is the differential form of state variable 1. State variable 10; This is the differential form of state variable 2. and These are the proportional and integral coefficients in the PI control of the PLL, respectively. This is the differential form of state variable 3. This is the nonlinear term corresponding to state variable 6. State variable 5, State variable 6; This is the differential form of state variable 4. This represents the reference value for the voltage of the grid converter system. This represents the reference value for the current in the grid converter system. This represents the q-axis current gain for typical reactive current control. State variable 9; This is the differential form of state variable 5. This is the reactive current value under normal operating conditions. Let the state variable be 1. For state variable 3, and These are the proportional and integral coefficients in the PI control of the PLL, respectively. , These are the proportional and integral coefficients of the current loop PI controller. For filtering inductors, Represented as filter resistor, This is the nonlinear term corresponding to state variable 1. This refers to the nonlinear term corresponding to state variable 10; The differential form of state variable 6, This is the active current value under normal operating conditions; This is the differential form of state variable 7. Represented as grid-side line resistance, Represented as grid-side line inductance, Represented as grid voltage, It is expressed as the sine value of the phase angle difference between the grid-type converter and the power grid under steady-state conditions; The differential form of state variable 8, It is expressed as the cosine of the phase angle difference between the grid-connected converter and the power grid under steady-state conditions. For weighting functions; This is the differential form of state variable 9. Represented as common capacitor, This represents the q-axis value of the PCC voltage under steady-state conditions. The differential form of state variable 10, This represents the d-axis value of the PCC voltage under steady-state conditions.

[0066] (13) in, This is the generation term of the integrator in steady-state phase-locked loop PI control. This represents the q-axis value of the PCC voltage under steady-state conditions.

[0067] (14) in, These are the fitting coefficients. To match the reactive current value of the grid-type converter in normal mode, This is a reference value for the reactive current of the grid-type converter in normal mode. This is the current limiting value.

[0068] Integrating all the local linear models, the TS fuzzy model of the grid converter system is obtained as shown in formula (15): (15) in, Represented as a TS fuzzy model, Represents the weighting function. Represented as a coefficient matrix, It is represented as an intermediate variable.

[0069] The stability criterion of this invention is given by the linear matrix inequality (LMI) of formula (16), when each matrix in formula (15) is stable. When all conditions satisfy the LMI solvability condition of formula (16), the nonlinear system is asymptotically stable, and a constant matrix M can be automatically generated. The condition for the existence of M is that it is an arbitrary matrix. and All are Herwitz matrices.

[0070] (16) in, It is represented as a constant matrix, and r represents the number of elements.

[0071] Based on the TS fuzzy model, a grid-type converter system LF can be constructed as shown in formula (17), where M is a constant matrix that guarantees... According to the Lyapunov stability theorem, when the LMI of equation (16) has a solution, it guarantees that... If the nonlinear system is asymptotically stable, then the system is stable.

[0072] (17) Based on the constructed LF, the EDA of the system can be characterized to evaluate stability. The EDA directly reflects the system's disturbance rejection capability at its operating point; a larger range indicates stronger system stability. The characterization of the EDA includes the following steps A1-A4: A1. Initialize the state variables of the nonlinear term and (i=1, 2…r).

[0073] A2. Solving the coefficient matrix (i=1, 2…r).

[0074] A3, will Substituting into the LMI in formula (16), if the LMI has a solution, the constant matrix M in the LF can be obtained, according to the iteration step size. Increase , reduce Then, proceed to A2.

[0075] A4. If LMI has no solution, then use M from the previous step. and Characterize EDA and project it onto - ( ) plane, such as Figures 6-8 As shown, the transient stability of the grid converter system is quantitatively estimated.

[0076] The initial point in the LVRT process is the equilibrium point of the normal control mode, which can be obtained by setting the differential terms of formulas (5)-(8) and (18) to zero. Similarly, the equilibrium point of the LVRT mode can be obtained by setting the differential terms of formulas (2)-(8) to zero. The expressions for the initial point and the equilibrium point are shown in formula (19).

[0077] (18) in, for The differential form, for The differential form, This is the integrator output in the d-axis power loop PI control. This is the integrator output in the q-axis power loop PI control. and These are the active and reactive power command values, respectively. and These represent the actual active and reactive power outputs, respectively. for The differential form, for The differential form, yes d The output of the integrator in shaft current loop PI control yes q The output of the integrator in shaft current loop PI control and This is expressed as the proportional and integral coefficients of the active power loop PI controller. and This represents the proportional and integral coefficients of the reactive power loop PI controller. It is the inductor current. d Axial components, It is the inductor current. q Axial components.

[0078] (19) in, The initial point before and after the voltage drop occurs. This represents the equilibrium point before and after a voltage drop. and These are the state variables of the differential equation model in normal mode and LVRT mode, respectively.

[0079] S3: Analyze the impact of control parameters on the transient stability of the grid converter by estimating the attraction domain.

[0080] (1) The effect of PLL parameters on the transient stability of LVRT switching: While keeping other parameters consistent with Table 1, for Figure 3 The unstable operating condition shown in (b) Figure 6 (a) provides different PLL scaling factors. The EDA changes of the following grid converter system, with As the value increases, the EDA range of the grid converter system expands, and the transient stability is enhanced accordingly. Figure 6 (a) It can be seen that when When = 0.1, the initial point A is outside the EDA, indicating that the grid converter system has a risk of instability. When increased to 0.5, EDA expands to include the initial point A, indicating that the grid converter system can maintain transient stability during LVRT. When further increased to 1.0, EDA continues to expand, resulting in better transient stability of the grid converter system.

[0081] Figure 6 (b) gives Figure 3 (b) Different PLL integral coefficients under the operating conditions shown The impact of EDA on grid-type converter systems. With... The reduction in [value] leads to an increase in the EDA range of the mesh converter system, and consequently, enhanced transient stability. Figure 6 (b) It can be seen that when When the initial point A is outside the EDA, it indicates that the grid converter system is at risk of instability. When reduced to 0.19, the EDA expands to include the initial point A, indicating that the grid converter system can maintain transient stability during LVRT. When further reduced to 0.38, the EDA continues to increase, resulting in better transient stability compared to the mesh converter system. However, despite the reduction... It is beneficial to the LVRT transient process of the grid-type converter system, but if Reducing it to 0 (i.e., eliminating the PLL integral stage) will cause the PLL to have a frequency tracking deviation, which will cause the voltage drop fault to cause the grid converter system to lose its balance point, thus triggering transient instability.

[0082] (2) The influence of current loop parameters on the transient stability of LVRT switching.

[0083] Figure 7 (a) gives Figure 3 (b) shows the proportional coefficients of different current loops under the operating conditions. The impact of EDA on grid-type converter systems. With... The reduction in [value] leads to an increase in the EDA range of the mesh converter system, and consequently, enhanced transient stability. Figure 5 (a) It can be seen that when When the initial point A is outside the EDA at a value of 5.3, it indicates that the grid converter system is at risk of instability. When reduced to 3.3, the EDA expands to include the initial point A, indicating that the grid converter system can maintain transient stability during LVRT. When further reduced to 2.3, the EDA continues to increase, resulting in better system stability compared to the mesh converter.

[0084] Figure 7 (b) gives Figure 3 (b) shows the integral coefficients of different current loops under the operating conditions. The impact of EDA on grid-type converter systems. With... The decrease in [something] corresponds to the EDA range of the grid converter system first expanding and then shrinking, and the transient stability first increasing and then decreasing. [This is due to...] Figure 7 (b) It can be seen that when When the initial point A is outside the EDA, it indicates that the grid converter system is at risk of instability. When reduced to 500, EDA expands to include the initial point A, indicating that the grid converter system can maintain transient stability during LVRT. When the value is further reduced to 300, the EDA does not continue to expand but instead shrinks, causing the initial point A to fall outside the EDA again, and the grid converter system faces the risk of instability once more. The above results indicate that... Small variations in the value have a significant impact on the transient stability of the grid converter system, and a reasonable value needs to be selected.

[0085] (3) The effect of SCR on the transient stability of LVRT switching.

[0086] by Figure 3 Taking the operating condition shown as an example, the EDA of the grid converter system is plotted at SCR values ​​of 2.9 and 2, respectively, and projected onto the screen. Plane, such as Figure 8 As shown. Figure 8In the diagram, A and B represent the initial points before the system fault when the SCR is 2.9 and 2, respectively, and O is the equilibrium point after the fault. It can be seen that as the SCR increases, the grid strength strengthens, the EDA range expands, and the transient stability of the grid-connected converter system improves. When SCR = 2, the initial point B is outside the corresponding EDA, indicating that the grid-connected converter system has a risk of instability. However, when the SCR increases to 2.9, the EDA expands to include the corresponding initial point A, indicating that the grid-connected converter system can maintain transient stability during the LVRT process. The relationship between the initial point and EDA, and the change of the EDA range with SCR, are discussed. Figure 3 The simulation results are consistent.

[0087] S4: Based on the analysis of the impact of control parameters on the transient stability of the grid-type converter, the transient stability of the grid-type converter during the low-voltage ride-through switching process is improved by optimizing the control parameters to expand the attraction domain.

[0088] Example 3, referring to Figures 9-14 This invention provides a method for improving the low-voltage ride-through transient stability of a grid-type converter based on the TS fuzzy model and attraction domain estimation. To verify the beneficial effects of this invention, scientific demonstration is carried out through experiments.

[0089] A grid-connected system with a grid-connected converter was built using Matlab / Simulink software and a hardware-in-the-loop experimental platform. The system parameters of the grid-connected converter are shown in Table 1.

[0090] The simulation conditions are as follows: at t=0s, the grid converter is in normal operation control state; at 0.6s, the grid converter system experiences a voltage drop, and the grid converter switches to LVRT control.

[0091] Simulation 1: Operating conditions of the influence of PLL parameters on the transient stability of LVRT switching.

[0092] Figure 9 (a) Time-domain simulation comparisons demonstrate the different The time-domain simulation waveform is as follows: When the value is 0.1, the LVRT switching of the grid converter system fails, while when... When the value is increased to 0.5 and 1.0, the LVRT switching is successful after a transient process of approximately 0.05 seconds following the connection of the grid converter system. The phase trajectory after the grid converter system experiences a fault is projected onto... - Phase plane, such as Figure 9 (b) Comparison with the operating phase trajectory of the grid converter system. It can be seen that point A is the initial steady-state point of the grid converter system. After a voltage drop, when... When the value is 0.1, point A is outside the EDA, and the network converter system becomes unstable along the blue curve starting from point A, failing to converge to the equilibrium point O; when When the value is increased to 0.5 and 1.0, point A lies within the EDA, and the operating state of the grid converter system converges from point A along the red and green curves to the equilibrium point O, respectively. The simulation results above verify that increasing the value... This can improve the transient stability of the LVRT in a grid-type converter system. Similarly, Figure 10 The time-domain simulation waveforms under different kipll conditions are shown, among which Figure 10 (a) Comparison of time-domain simulations, Figure 10 (b) To compare with the operating phase trajectory of the grid converter system, the reduction of... It can also improve the transient stability of the LVRT system with the grid converter.

[0093] Simulation 2: Operating conditions under which current loop parameters affect the transient stability of LVRT switching.

[0094] Figure 11 (a) Time-domain simulation comparisons demonstrate the different The time-domain simulation waveform shows that after a fault occurs at 0.6 s, when... When the value is 700, the LVRT switching of the grid converter system fails, while when When the value is reduced to 500, after a transient process of approximately 0.25 seconds, the LVRT switching with the mesh converter system is successful. When the value was further reduced to 300, the LVRT switching of the grid converter system failed again. The phase trajectory after the grid converter system failure was projected onto... - On the phase plane, such as Figure 11 (b) Comparison with the operating phase trajectory of the grid converter system. It can be seen that point A is the initial steady-state point of the grid converter system. After a voltage drop, when... When the values ​​are 700 and 300 respectively, point A is located outside the corresponding EDA, and the operating state of the mesh converter destabilizes along the blue and green curves respectively starting from point A; when When the value is 500, point A is located within EDA, and the operating state of the mesh converter converges from point A along the red curve to the equilibrium point O. The above simulation results verify that different The validity of the EDA. Similarly, Figure 12 Showing different The simulated waveforms below verify the reduction It can improve the LVRT transient stability of the grid converter system. Among them, 12(a) is a time-domain simulation comparison and 12(b) is a comparison of the phase trajectory of the grid converter system.

[0095] Simulation 3: Operating conditions of the effect of SCR on the transient stability of LVRT switching.

[0096] by Figure 3 Taking the working condition shown as an example, Figure 3 When the SCR is 2.9 and 2, the phase trajectory projection after a fault occurs in the grid converter system is shown. - Phase plane. For example... Figure 13 As shown, after a voltage drop fault, when the SCR is 2.9, the initial point A of the grid converter system is located within the corresponding EDA, and the operating state converges from point A along the green curve to the equilibrium point O. However, when the SCR decreases to 2, the initial point B of the grid converter system is located outside the corresponding EDA, and the operating state becomes unstable from point B along the blue curve. This result is consistent with... Figure 3 The simulation results are consistent with those in the paper, which verifies that as the SCR decreases, the transient stability of the LVRT of the grid converter system decreases. It also further verifies the effectiveness of the EDA calculated by the method in this paper.

[0097] The experimental conditions were as follows: the grid converter system was connected to the grid at t=0s, and the grid voltage was set to drop to 0.65pu at t=10s.

[0098] Experiment 1: Large Disturbance Instability Conditions of LVRT Processes under Different SCR Conditions Set the SCR to two operating conditions: 2.9 and 2. Figure 14 (a) As shown in SCR=2.9, when SCR=2.9, the initial point of the grid converter system is located inside the EDA, and after switching to LVRT control, it can converge to the equilibrium point after the voltage drop; while Figure 14 (b) As shown in SCR=2, when SCR=2, the initial point is located outside the EDA, and the grid converter system exhibits instability. Experimental results and... Figure 3 and Figure 8 The simulation results are consistent, indicating that the EDA characterized by the method in this paper can accurately determine the transient stability of the grid converter system under large disturbances, and verifying its high reliability.

[0099] Experiment 2: Improving the transient stability of LVRT by optimizing control parameters against Figure 3 (b) illustrates the unstable operating condition. Based on the analysis of the impact of parameter variations on the transient stability of the grid-connected converter system, the transient stability of the grid-connected converter system is improved by optimizing the control parameters to increase the EDA. The current loop proportional gain is used as an example. For example, After reducing the voltage from 5.3 to 3.3, the grid converter system was able to stably converge to the equilibrium point after the voltage drop, such as... Figure 14As shown in (c), the experimental results are consistent with the theoretical and simulation analysis, verifying the effectiveness of the parameter optimization method.

[0100] This embodiment also provides an electronic device applicable to a low-voltage ride-through transient stability improvement method for a grid-connected converter based on a TS fuzzy model and attraction domain estimation, comprising: a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to implement the low-voltage ride-through transient stability improvement method for a grid-connected converter based on a TS fuzzy model and attraction domain estimation as proposed in the above embodiment.

[0101] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements a low-voltage ride-through transient stability improvement method for a grid-type converter based on a TS fuzzy model and attraction domain estimation, as proposed in the above embodiment.

[0102] The storage medium proposed in this embodiment and the method for improving the low voltage ride-through transient stability of a grid-type converter based on TS fuzzy model and attraction domain estimation proposed in the above embodiments belong to the same inventive concept. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.

[0103] Based on the above description of the implementation methods, those skilled in the art can clearly understand that the present invention can be implemented using software and necessary general-purpose hardware, and of course, it can also be implemented using hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0104] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for improving the low-voltage ride-through transient stability of a grid-connected converter based on a TS fuzzy model and attraction domain estimation, characterized in that: include, The non-differentiable characteristics of low-voltage ride-through limiting control are handled by using a logarithmic-exponential composite function, and a full-order nonlinear differential equation model considering low-voltage ride-through limiting control is established. The estimated attraction region is characterized using the TS fuzzy model and linear matrix inequalities; The influence of control parameters on the transient stability of the grid converter is analyzed by estimating the attraction domain. Based on the analysis of the impact of control parameters on the transient stability of the grid-type converter, the transient stability of the grid-type converter during the low-voltage ride-through switching process is improved by optimizing the control parameters to expand the attraction domain.

2. The method for improving the low-voltage ride-through transient stability of a grid-connected converter based on a TS fuzzy model and attraction domain estimation as described in claim 1, characterized in that: The establishment of the full-order nonlinear differential equation model considering low-voltage ride-through limiting control includes establishing the mathematical model of low-voltage ride-through control, the mathematical model of phase-locked loop, the mathematical model of current loop, and the mathematical model of main circuit. The mathematical model for establishing low-voltage ride-through control includes the following: when a large disturbance causes the grid-connected converter to enter low-voltage ride-through mode, the fluctuation of the terminal voltage will cause the reactive current control to switch between saturation and desaturation. Follow Dynamic changes: in, This is expressed as a reference value for reactive current. This is a reference value for the reactive current of the grid-type converter in normal mode. Represented as terminal voltage, This represents the reference value for the voltage of the grid converter system. This represents the reference value for the current in the grid converter system. This is the current limiting value. This represents the q-axis current gain for typical reactive current control. Current limiting factor, This is expressed as a reference value for active current. This is the reference value for the active current of the grid-type converter in normal mode.

3. The method for improving the low-voltage ride-through transient stability of a grid-connected converter based on a TS fuzzy model and attraction domain estimation as described in claim 2, characterized in that: The mathematical model of the phase-locked loop is expressed as follows: in, This is the generation term of the integrator in phase-locked loop PI control. To track the q-axis component of the voltage at PCC in the grid-type converter, Represented as The differential form, It is expressed as the phase angle difference between the grid-type converter and the power grid. Represented as Differential form, and These are the proportional and integral coefficients in the PI control of the PLL, respectively. The mathematical model of the current loop is expressed as follows: in, Represented as The differential form, Represented as The differential form, , These represent the outputs of the integrator in the d-axis current loop PI control and the q-axis current loop PI control, respectively. This is expressed as a reference value for the inductor current on the d-axis. This is expressed as a reference value for the inductor current on the q-axis. This is expressed as the actual value of the inductor current on the d-axis. This is expressed as the actual value of the inductor current on the q-axis. , These are the proportional and integral coefficients of the current loop PI controller. To provide a reference value for the d-axis of the port voltage of the grid converter. This is the q-axis reference value for the port voltage of the grid converter. For filtering inductors, This represents the q-axis value of the PCC voltage. The mathematical model of the main circuit is expressed as follows: in, Represented as The differential form, This is expressed as the actual value of the inductor current on the d-axis. This is the output of the integrator in the d-axis current loop PI control. , These are the proportional and integral coefficients of the current loop PI controller. and These are the proportional and integral coefficients in the PI control of the PLL, respectively. For filtering inductors, Represented as filter resistor, To track the q-axis component of the voltage at PCC in the grid-type converter, To match the d-axis value of the voltage at PCC in the grid-type converter, Represented as The differential form, This is expressed as the actual value of the inductor current on the q-axis. This is expressed as a reference value for the inductor current on the q-axis. This is the output of the integrator in the q-axis current loop PI control. Represented as The differential form, Represented as common capacitor, Represented as the grid angular frequency, This represents the grid-side inductor current at the d-axis common junction point PCC. Represented as The differential form, This represents the grid-side inductor current at the q-axis common junction point PCC. Represented as The differential form, Represented as grid-side line resistance, Represented as grid-side line inductance, Represented as grid voltage, It is expressed as the phase angle difference between the grid-type converter and the power grid. It is expressed as the cosine of the phase angle difference between the grid-connected converter and the power grid. Represented as The differential form, It is expressed as the sine value of the phase angle difference between the grid-type converter and the power grid.

4. The method for improving the low-voltage ride-through transient stability of a grid-connected converter based on a TS fuzzy model and attraction domain estimation as described in claim 3, characterized in that: Based on the mathematical models of low-voltage ride-through control, phase-locked loop, current loop, and main circuit, a full-order nonlinear differential equation model is obtained, expressed as: in, Represented as Differential form, This is the generation term of the integrator in phase-locked loop PI control. To track the q-axis component of the voltage at PCC in the grid-type converter, Represented as The differential form, It is expressed as the phase angle difference between the grid-type converter and the power grid. and These are the proportional and integral coefficients in the PI control of the PLL, respectively. Represented as The differential form, Represented as The differential form, , These represent the outputs of the integrator in the d-axis current loop PI control and the q-axis current loop PI control, respectively. This is expressed as a reference value for the inductor current on the d-axis. This is expressed as a reference value for the inductor current on the q-axis. This is expressed as the actual value of the inductor current on the d-axis. This is expressed as the actual value of the inductor current on the q-axis. Represented as The differential form, This is expressed as the actual value of the inductor current on the d-axis. This is the output of the integrator in the d-axis current loop PI control. This is expressed as a reference value for the inductor current on the d-axis. , These are the proportional and integral coefficients of the current loop PI controller. and These are the proportional and integral coefficients in the PI control of the PLL, respectively. This is expressed as the actual value of the inductor current on the q-axis. To match the d-axis value of the voltage at PCC in the grid-type converter, This is the generation term of the integrator in phase-locked loop PI control. For filtering inductors, Represented as filter resistor, Represented as The differential form, This is expressed as a reference value for the inductor current on the q-axis. This is the output of the integrator in the q-axis current loop PI control. To track the q-axis component of the voltage at PCC in the grid-type converter, Represented as The differential form, Represented as common capacitor, This represents the grid-side inductor current at the d-axis common junction point PCC. Represented as the grid angular frequency, Represented as The differential form, This represents the grid-side inductor current at the q-axis common junction point PCC. Represented as The differential form, Represented as grid-side line resistance, Represented as grid-side line inductance, Represented as grid voltage, It is expressed as the phase angle difference between the grid-type converter and the power grid. It is expressed as the cosine of the phase angle difference between the grid-connected converter and the power grid. Represented as The differential form, It is expressed as the sine value of the phase angle difference between the grid-type converter and the power grid.

5. The method for improving the low-voltage ride-through transient stability of a grid-connected converter based on a TS fuzzy model and attraction domain estimation as described in claim 4, characterized in that: The characterization and estimation of the attraction domain includes, Construct the Lyapunov functions for the root-mesh converter system; Initialize the state variables of the nonlinear term and ; Solve for the coefficient matrix; Substituting the coefficient matrix into the linear matrix inequality, if the linear matrix inequality has a solution, then the constant matrix in the Lyapunov function of the grid converter system is obtained. Increase according to the iteration step size , reduce Then, solve for the coefficient matrix; If the linear matrix inequality has no solution, then a constant matrix M and state variables are used. and Describe and estimate the attraction domain.

6. The method for improving the low-voltage ride-through transient stability of a grid-connected converter based on a TS fuzzy model and attraction domain estimation as described in claim 4, characterized in that: The TS fuzzy model is represented as follows: in, Represented as a TS fuzzy model, Represents the weighting function. Represented as a coefficient matrix, Represented as the corresponding state variables, Represented as an intermediate variable; The linear matrix inequality is expressed as follows: in, Represented as a constant matrix, It is represented as a coefficient matrix, where r represents the number of elements.

7. The method for improving the low-voltage ride-through transient stability of a grid-connected converter based on a TS fuzzy model and attraction domain estimation as described in claim 4, characterized in that: The analysis of the impact of control parameters on the transient stability of the grid converter includes: The effects of phase-locked loop, current loop, and SCR parameters on the transient stability of a grid-connected converter during low-voltage ride-through are analyzed using the estimated attraction domain.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of any one of claims 1 to 7: a method for improving the low-voltage ride-through transient stability of a grid-type converter based on a TS fuzzy model and attraction domain estimation.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the low-voltage ride-through transient stability improvement method for a grid-type converter based on the TS fuzzy model and attraction domain estimation as described in any one of claims 1 to 7.

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