Parameter design method for transient stability improvement of network-forming converter under asymmetric fault

Abstract

The application relates to the technical field of new energy power generation transient stability parameter design, and discloses a parameter design method for transient stability improvement under asymmetric fault of grid-connected type converter, which comprises the following steps: calculating a virtual inertia lower limit based on a maximum frequency change rate constraint; solving a transient synchronous stability boundary based on a transient synchronous stability constraint; and obtaining a parameter feasible region that simultaneously satisfies the maximum frequency change rate constraint and the transient synchronous stability constraint. According to the application, the parameter feasible region of damping and inertia is depicted on the basis of considering the frequency change rate constraint and the transient synchronous stability constraint; and the parameter design method can be used for parameter design of the grid-connected type converter under asymmetric fault for the purpose of transient stability improvement.

Description

Technical Field

[0001] This application relates to the field of transient stability parameter design technology for new energy power generation, specifically a parameter design method for improving transient stability under asymmetrical faults in grid-connected converters. Background Technology

[0002] Compared to grid-connected converters, grid-connected converters have better active voltage and frequency support capabilities and have received widespread attention in recent years. However, under asymmetrical grid faults, grid-connected converters may suffer from serious transient stability problems, mainly including transient synchronization stability problems and frequency stability problems.

[0003] Reasonable parameter design is crucial for the transient synchronization stability and frequency stability of grid-connected converters. The rate of change of frequency (RoCoF), a key indicator of frequency stability, is explicitly required by IEEE Std 1547-2018 to not exceed 3 Hz / s. Existing technologies suggest that virtual inertia can improve system frequency stability, but it can worsen transient synchronization stability. Other existing technologies propose using well-designed virtual inertia and damping to meet the rate of change of frequency requirements while ensuring transient synchronization stability, but these are limited to symmetrical faults. However, based on grid operation experience, the proportion of asymmetrical faults in power grids is far higher than that of symmetrical faults.

[0004] Therefore, a parameter design method is proposed to satisfy the transient synchronous stability constraint and frequency change rate constraint of the grid-type converter under asymmetric faults, which is of great significance for the safe and stable operation of the system. Summary of the Invention

[0005] The purpose of this application is to provide a parameter design method for improving transient stability under asymmetric faults in a grid-type converter, so as to solve the technical problem that it is difficult to simultaneously satisfy the maximum rate of change of frequency constraint and the transient synchronous stability constraint in the prior art.

[0006] To achieve the above objectives, this application provides a parameter design method for improving transient stability under asymmetric faults in a grid-type converter, the method comprising: Calculate the lower limit of virtual inertia based on the maximum rate of change of frequency constraint; Solve the transient synchronization stability boundary based on transient synchronization stability constraints; Obtain the feasible region of parameters that simultaneously satisfy the maximum rate of change of frequency constraint and the transient synchronization stability constraint.

[0007] As a preferred option, the lower bound of virtual inertia The expression is: in: This is a positive-sequence active power command. The positive sequence voltage at the point of common coupling (PCC) The voltage amplitude of the power grid. This is the equivalent coefficient for negative sequence voltage. The negative sequence voltage at the point of common coupling (PCC) The initial angle of attack, and For equivalent reactance, This represents the maximum rate of change of frequency.

[0008] As a preferred method, the solution to the transient synchronization stability boundary is as follows: By iterating the energy function under different combinations of parameters for damping and virtual inertia, a transient synchronous stability boundary with a transient stability margin of 0 is obtained.

[0009] As a preferred option, the energy function The expression is: in, For virtual inertia, It is the positive sequence angular frequency. The rated angular frequency, and For equivalent reactance, The positive sequence voltage at the point of common coupling (PCC) This is a positive-sequence active power command. For positive sequence work angles, The voltage amplitude of the power grid. This is the reactive power droop factor. This is a positive sequence voltage command. This is a positive-sequence reactive power command. This is the equivalent coefficient for negative sequence voltage. The negative sequence voltage at the point of common coupling (PCC) Also the equivalent reactance, This is a negative sequence voltage command. This is a negative sequence reactive power command. The damping coefficient is... , This is the initial work angle.

[0010] As a preferred option, equivalent reactance , and and negative sequence voltage equivalent coefficient The expression is determined based on the type of asymmetrical fault, which includes single-phase-to-ground short circuit, two-phase short circuit, and two-phase short-to-ground fault.

[0011] Preferably, the transient stability margin is calculated for a grid-type converter system, and the calculation includes the following steps: Calculate the initial energy using the equilibrium point before the fault; The critical energy is calculated from the unstable equilibrium point during asymmetric failure; The transient stability margin is calculated based on the initial energy and the critical energy. The transient stability margin is equal to the difference between the critical energy and the initial energy.

[0012] As a preferred method, the calculation of the initial energy and critical energy includes the following steps: Substituting the pre-fault equilibrium point into the energy function Obtain initial energy ; Substituting the unstable equilibrium point during asymmetric faults into the energy function Calculate the critical energy .

[0013] As a preferred option, the initial equilibrium point of the grid-type converter system The expression is: in: , This is the rated angular frequency; , The reactance from the point of common coupling (PCC) to the fault point. This refers to the reactance from the fault point to the grid.

[0014] As a preferred option, the unstable equilibrium point of the grid-type converter system during asymmetrical faults. The expression is: in: , This is the rated angular frequency; .

[0015] As a preferred approach, the feasible region of parameters that simultaneously satisfies the maximum rate of change constraint and the transient synchronization stability constraint is characterized by taking the intersection of the lower limit of the virtual inertia that satisfies the maximum rate of change constraint and the transient synchronization stability boundary with a transient stability margin of 0.

[0016] Beneficial effects: The parameter design method for improving transient stability of grid-type converters under asymmetric faults in this application, based on the constraints of frequency change rate and transient synchronous stability, characterizes the parameter feasible region of damping and inertia; it can be used for parameter design of grid-type converters for improving transient stability under asymmetric faults. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating the parameter design method for improving transient stability of a grid-type converter under asymmetric fault conditions, as provided in this application embodiment. Figure 2 This is a control structure diagram of a grid-type converter system provided in an embodiment of this application; Figure 3 The parameter design method for improving transient stability in a grid-type converter under asymmetrical faults provided in this application embodiment obtains the parameter feasible domain when the asymmetrical fault is a two-phase short-circuit to ground. Figure 4 Provided for the embodiments of this application Figure 2 Points in region C Simulation results diagram; Figure 5 Provided for the embodiments of this application Figure 2 Points in region A Simulation results diagram; Figure 6 Provided for the embodiments of this application Figure 2 Points in the feasible region Simulation results diagram; Figure 7 A flowchart illustrating the parameter design for improving transient stability of a grid-type converter under asymmetric fault conditions, as provided in this application embodiment.

[0019] The implementation, functional features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] In this document, the term "comprising" is intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0022] To meet the transient synchronous stability constraints and frequency change rate constraints of grid-type converters under asymmetric faults, this embodiment discloses a parameter design method for improving transient stability of grid-type converters under asymmetric faults.

[0023] Reference Figure 1 , Figure 1 A flowchart illustrating the parameter design method for improving transient stability of a grid-type converter under asymmetric fault conditions, as provided in this application embodiment.

[0024] like Figure 1 As shown in the figure, this embodiment discloses a parameter design method for improving transient stability under asymmetric faults in a grid-type converter. The method includes: S10: Calculate the lower limit of virtual inertia based on the maximum rate of change constraint; in this embodiment, the maximum rate of change constraint is determined based on IEEE Std 1547-2018.

[0025] S20: Solve the transient synchronization stability boundary based on transient synchronization stability constraints.

[0026] S30: Obtain the feasible region of parameters that simultaneously satisfy the maximum rate of change of frequency constraint and the transient synchronization stability constraint.

[0027] Reference Figure 2 , Figure 2 This is a control structure diagram of a grid-type converter system provided in an embodiment of this application.

[0028] like Figure 2 As shown, in the main circuit section, the inverter and the filter circuit are connected in sequence, and the filter circuit is connected to the power grid. The reactance from the point of common coupling (PCC) to the fault point. The reactance from the fault point to the grid end. This is the grounding reactance. and It refers to the filter inductor and its parasitic resistance. It is a filter capacitor. This is the DC-side voltage, which can be considered a DC source with a constant amplitude. The grid voltage amplitude is... The phase angle is ,by Use it as a reference phase angle and set it to 0 degrees.

[0029] Therefore, the positive-sequence active-frequency control equation of the grid converter can be expressed by equation (1): (1) in: and These are the damping coefficient and the virtual inertia, respectively. and These are the positive-sequence active power command and the instantaneous value, respectively. The rated angular frequency, It is the positive sequence angular frequency. The phase angle is in positive sequence. For positive sequence work angles, It is a negative sequence angular frequency. It is a negative phase angle. This is the positive sequence voltage of PCC. This is the negative sequence voltage of PCC.

[0030] The expression for the rate of change of frequency is: (2) From equation (2), we can obtain the lower limit of the virtual inertia that satisfies the maximum rate of change of frequency.

[0031] Specifically, the lower limit of virtual inertia The expression is: (3) in: This is a positive-sequence active power command. The positive sequence voltage at the point of common coupling (PCC) The voltage amplitude of the power grid. This is the equivalent coefficient for negative sequence voltage. The negative sequence voltage at the point of common coupling (PCC) The initial angle of attack, and For equivalent reactance, This represents the maximum rate of change of frequency.

[0032] The positive-sequence reactive-voltage control equation and the negative-sequence reactive-voltage control equation can be expressed by (2): (4) in: and These are the reactive droop coefficient and the inertia coefficient, respectively. and These are the positive-sequence reactive power command and the instantaneous value, respectively. This is a positive sequence voltage command; and These are the negative-sequence reactive power command and the instantaneous value, respectively. This is a negative sequence voltage command.

[0033] Specifically, in equation (4), the equivalent reactance , and and negative sequence voltage equivalent coefficient The expression is determined based on the type of asymmetrical fault, which includes single-phase-to-ground short circuit, two-phase short circuit, and two-phase short-circuit to ground, and the corresponding equivalent reactance. , and and negative sequence voltage equivalent coefficient The expression is: For a single-phase ground fault: (5) For a two-phase short circuit: (6) For a two-phase short-circuit ground: (7) in, The reactance from the point of common coupling (PCC) to the fault point. Represents parallel connection, The reactance from the fault point to the grid end. This is the grounding reactance.

[0034] Multiply both sides of the positive-sequence active-frequency equation shown in equation (1) After the first integration, we obtain equation (8) as follows: in, As potential energy, As kinetic energy, To dampen energy dissipation, It is a constant. , This is the initial work angle.

[0035] Equation (8) can be transformed into equation (9) as shown below through integral transformation: in, It is a constant.

[0036] Based on theoretical foundations, the specific method for solving the transient synchronization stability boundary is as follows: By iterating the energy function under different combinations of parameters for damping and virtual inertia, a transient synchronous stability boundary with a transient stability margin of 0 is obtained.

[0037] Based on equation (9), this embodiment constructs the energy function shown below. The expression is as follows: (10) in, For virtual inertia, It is the positive sequence angular frequency. The rated angular frequency, and For equivalent reactance, The positive sequence voltage at the point of common coupling (PCC) This is a positive-sequence active power command. For positive sequence work angles, The voltage amplitude of the power grid. This is the reactive power droop factor. This is a positive sequence voltage command. This is a positive-sequence reactive power command. This is the equivalent coefficient for negative sequence voltage. The negative sequence voltage at the point of common coupling (PCC) Also the equivalent reactance, This is a negative sequence voltage command. This is a negative sequence reactive power command. The damping coefficient is... , This is the initial work angle.

[0038] Specifically, the calculation of transient stability margin is for grid-type converter systems, and the calculation includes the following steps: Calculate the initial energy using the equilibrium point before the fault; The critical energy is calculated from the unstable equilibrium point during asymmetric failure; The transient stability margin is calculated based on the initial energy and the critical energy. The transient stability margin is equal to the difference between the critical energy and the initial energy.

[0039] Specifically, the calculation of initial energy and critical energy includes the following steps: Substituting the pre-fault equilibrium point into the energy function Obtain initial energy ; Substituting the unstable equilibrium point during asymmetric faults into the energy function Calculate the critical energy .

[0040] Specifically, the initial equilibrium point of a grid-type converter system The expression is: in: , This is the rated angular frequency; , The reactance from the point of common coupling (PCC) to the fault point. This refers to the reactance from the fault point to the grid.

[0041] Specifically, the initial equilibrium point of a grid-type converter system The expression is: in: , This is the rated angular frequency; .

[0042] In this specific application, the initial equilibrium point of the system is substituted into the energy function. Obtain initial energy Substitute the unstable equilibrium point during the asymmetric failure of the system into the energy function. Obtaining critical energy .

[0043] Transient stability margin of the system Represented as: .

[0044] Specifically, the feasible region of parameters that simultaneously satisfies the maximum rate of change of frequency constraint and the transient synchronization stability constraint is characterized by taking the intersection of the lower limit of virtual inertia that satisfies the maximum rate of change of frequency constraint and the transient synchronization stability boundary with a transient stability margin of 0.

[0045] In the specific application of this embodiment, the energy function is iterated under different combinations of parameters for damping and virtual inertia to obtain the transient synchronization stability boundary with a transient stability margin of 0. The intersection of the lower limit of virtual inertia satisfying the maximum rate of change constraint and the transient synchronization stability boundary with a transient stability margin of 0 yields the parameter feasible region of damping and inertia that simultaneously satisfies both the maximum rate of change constraint and the transient synchronization stability constraint.

[0046] Based on the above, the parameter design method for improving transient stability of grid-type converters under asymmetrical faults proposed in this embodiment improves the transient synchronization stability and frequency stability of grid-type converters under asymmetrical faults, provides quantitative guidance for practical engineering applications, and provides a feasible solution for parameter design of grid-type converters under asymmetrical faults.

[0047] The application effect of the parameter design method for improving transient stability under asymmetrical faults in a grid-type converter disclosed in this embodiment will now be explained.

[0048] Reference Figure 2 The parameters for this embodiment are shown in Table 1: Table 1 Reference Figure 3 , Figure 3 The parameter design method for improving transient stability in a grid-type converter under asymmetrical faults provided in this application embodiment obtains the parameter feasible region when the asymmetrical fault is a two-phase short-circuit to ground.

[0049] like Figure 3 As shown, the frequency change rate constraint is not satisfied in the region below the virtual inertia lower limit, and the transient synchronization stability constraint is not satisfied in the region to the left of the transient synchronization stability boundary.

[0050] Reference Figure 4 , Figure 4 Provided for the embodiments of this application Figure 2 Points in region C The simulation results are shown in the figure.

[0051] according to Figure 3 The feasible region for the parameters shown is the point in region C. The maximum rate of change constraint is not satisfied, but the transient synchronization stability constraint is satisfied. Simulation results are as follows: Figure 4 As shown, the simulation results indicate that the system can maintain transient synchronization stability, but the maximum frequency change rate is 3.5 Hz / s, which does not meet the requirement of IEEE Std 1547-2018 that the maximum frequency change rate should not exceed 3 Hz / s. This is consistent with the analysis results and verifies the effectiveness of the parameter design method.

[0052] Reference Figure 5 , Figure 5 Provided for the embodiments of this application Figure 2 Points in region A The simulation results are shown in the figure.

[0053] according to Figure 3 The feasible range of the parameters shown is for points in region A. The maximum rate of change of frequency constraint is satisfied, but the transient synchronization stability constraint is not satisfied. Simulation results are as follows: Figure 5 As shown, the simulation results indicate that the system is transiently unstable, and the maximum frequency change rate in the initial stage of the fault is 2.9 Hz / s, which is consistent with the analysis results and verifies the effectiveness of the parameter design method.

[0054] Reference Figure 6 , Figure 6 Provided for the embodiments of this application Figure 2 Points in the feasible region The simulation results are shown in the figure.

[0055] according to Figure 3 The parameters shown are feasible regions, and the points in the feasible regions are... The maximum rate of change constraint and the transient synchronization stability constraint are satisfied. Simulation results are as follows: Figure 6 As shown, the simulation results indicate that the system is transiently synchronous and stable, with a maximum frequency change rate of 2.9 Hz / s, which meets the requirement of IEEE Std 1547-2018 that the maximum frequency change rate should not exceed 3 Hz / s. This is consistent with the analysis results and verifies the effectiveness of the parameter design method.

[0056] Reference Figure 7 , Figure 7 This document presents a flowchart illustrating the parameter design for improving transient stability of a grid-type converter under asymmetrical fault conditions, as provided in an embodiment of this application. Figure 7 As shown, the parameter design for improving transient stability of the grid-type converter under asymmetric faults in this embodiment considers the constraints of frequency change rate and transient synchronous stability, and characterizes the parameter feasible region of damping and inertia, thus realizing the parameter design for improving transient stability of the grid-type converter under asymmetric faults.

[0057] In the embodiments provided in this application, it should be understood that the embodiments described herein can be implemented in hardware, software, firmware, middleware, code, or any suitable combination thereof. For hardware implementation, the processor may be implemented in one or more of the following: application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, other electronic units designed to implement the functions described herein, or combinations thereof. For software implementation, some or all of the processes of the embodiments may be performed by a computer program instructing the associated hardware. During implementation, the program may be stored in a computer-readable storage medium or transmitted as one or more instructions or code on a computer-readable storage medium. Computer-readable storage media include computer storage media and communication media, wherein communication media include any medium that facilitates the transmission of a computer program from one place to another. Storage media may be any available medium accessible to a computer. Computer-readable storage media may include, but are not limited to, RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage media or other magnetic storage devices, or any other medium capable of carrying or storing desired program code having the form of instructions or data structures and accessible to a computer.

[0058] Finally, it should be noted that the above description is only a preferred embodiment of this application and is not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A parameter design method for improving transient stability under asymmetric faults in a grid-type converter, characterized in that, The method includes: Calculate the lower limit of virtual inertia based on the maximum rate of change of frequency constraint; Solve the transient synchronization stability boundary based on transient synchronization stability constraints; Obtain the feasible region of parameters that simultaneously satisfy the maximum rate of change of frequency constraint and the transient synchronization stability constraint.

2. The parameter design method for improving transient stability under asymmetric faults in a grid-type converter according to claim 1, characterized in that, Virtual Inertia Lower Bound The expression is: in: This is a positive-sequence active power command. The positive sequence voltage at the point of common coupling (PCC) The voltage amplitude of the power grid. This is the equivalent coefficient for negative sequence voltage. The negative sequence voltage at the point of common coupling (PCC) The initial angle of attack, and For equivalent reactance, This represents the maximum rate of change of frequency.

3. The parameter design method for improving transient stability under asymmetric faults in a grid-type converter according to claim 1, characterized in that, The solution method for the transient synchronization stability boundary is as follows: By iterating the energy function under different combinations of parameters for damping and virtual inertia, a transient synchronous stability boundary with a transient stability margin of 0 is obtained.

4. The parameter design method for improving transient stability under asymmetric faults in a grid-type converter according to claim 3, characterized in that, Energy function The expression is: in, For virtual inertia, It is the positive sequence angular frequency. The rated angular frequency, and For equivalent reactance, The positive sequence voltage at the point of common coupling (PCC) This is a positive-sequence active power command. For positive sequence work angles, The voltage amplitude of the power grid. This is the reactive power droop factor. This is a positive sequence voltage command. This is a positive-sequence reactive power command. This is the equivalent coefficient for negative sequence voltage. The negative sequence voltage at the point of common coupling (PCC) Also the equivalent reactance, This is a negative sequence voltage command. This is a negative sequence reactive power command. The damping coefficient is... , This is the initial work angle.

5. The parameter design method for improving transient stability under asymmetric faults in a grid-type converter according to claim 4, characterized in that, Equivalent reactance , and and negative sequence voltage equivalent coefficient The expression is determined based on the type of asymmetrical fault, which includes single-phase-to-ground short circuit, two-phase short circuit, and two-phase short-to-ground fault.

6. The parameter design method for improving transient stability under asymmetric faults in a grid-type converter according to claim 4, characterized in that, The calculation of transient stability margin is for grid-type converter systems, and the calculation includes the following steps: Calculate the initial energy using the equilibrium point before the fault; The critical energy is calculated from the unstable equilibrium point during asymmetric failure; The transient stability margin is calculated based on the initial energy and the critical energy. The transient stability margin is equal to the difference between the critical energy and the initial energy.

7. The parameter design method for improving transient stability under asymmetric faults in a grid-type converter according to claim 6, characterized in that, The calculation of initial energy and critical energy includes the following steps: Substituting the pre-fault equilibrium point into the energy function Obtain initial energy ; Substituting the unstable equilibrium point during asymmetric faults into the energy function Calculate the critical energy .

8. The parameter design method for improving transient stability under asymmetric faults in a grid-type converter according to claim 7, characterized in that, Initial equilibrium point of a grid converter system The expression is: in: , This is the rated angular frequency; , The reactance from the point of common coupling (PCC) to the fault point. This refers to the reactance from the fault point to the grid.

9. The parameter design method for improving transient stability under asymmetric faults in a grid-type converter according to claim 7, characterized in that, Unstable equilibrium point of a grid converter system during asymmetrical faults The expression is: in: , This is the rated angular frequency; .

10. The parameter design method for improving transient stability under asymmetric faults in a grid-type converter according to claim 3, characterized in that, The feasible region of parameters that simultaneously satisfies the maximum rate of change of frequency constraint and the transient synchronization stability constraint is characterized by taking the intersection of the lower limit of the virtual inertia that satisfies the maximum rate of change of frequency constraint and the transient synchronization stability boundary with a transient stability margin of 0.

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