Method and device for evaluating voltage support strength of grid-connected system

Abstract

The invention provides a grid-connected system voltage support strength evaluation method and device, and the method comprises the steps: determining a closed-loop characteristic equation of a grid-connected system according to a current transfer function of a grid-connected point, calculating a critical short-circuit ratio of the grid-connected point according to the closed-loop characteristic equation of the grid-connected system, and achieving the evaluation of the voltage support strength of the grid-connected system. Compared with the prior art that the critical short-circuit ratio is obtained through time domain simulation, the process of obtaining the critical short-circuit ratio is high in efficiency, and the evaluation efficiency of the evaluation method can be improved. Moreover, the accuracy of the critical short-circuit ratio can be ensured, so that the real voltage support strength of the grid-connected system is accurately reflected, namely, the reliability of the evaluation method is relatively high. According to the invention, the impedance characteristic difference between the grid-following inverter and the grid-constructing inverter is fully considered, the calculation of the critical short-circuit ratio considers the output impedance of the grid-connected inverter, the influence of different control modes on the voltage support strength of the grid-connected system can be accurately quantified, and the voltage support strength of the grid-connected system can be evaluated more comprehensively.

Description

Technical Field

[0001] The present application relates to the technical field of new energy grid connection, and particularly relates to a method and device for evaluating the voltage support strength of a grid connection system. Background Technique

[0002] With the access of large-scale new energy, problems such as voltage control instability will occur in the grid connection system, and the severity is related to the voltage support strength of the grid connection system. Moreover, the access of grid-connected inverters with different control methods will affect the voltage support strength of the grid connection system. Therefore, it is necessary to evaluate the voltage support strength of the grid connection system.

[0003] Related technologies use the critical short-circuit ratio to evaluate the strength and static stability of the grid connection system after the DC is fed into the AC grid, that is, to evaluate the voltage support strength of the grid connection system during actual operation through the critical short-circuit ratio. However, the existing technology usually obtains the critical short-circuit ratio through time-domain simulation of the grid connection system. Since the simulation process requires continuous parameter adjustment, the parameter adjustment process is not only cumbersome but also relies on empirical judgment, resulting in low efficiency in obtaining the critical short-circuit ratio, and further leading to low evaluation efficiency of the voltage support strength. At the same time, the existing technology can only obtain the critical short-circuit ratio by the method of gradual approximation, and it is difficult to ensure the accuracy of the critical short-circuit ratio. That is to say, the obtained critical short-circuit ratio often has a certain error and is difficult to accurately reflect the true voltage support strength of the grid connection system. That is to say, the evaluation method provided by the related technology has low reliability. Summary of the Invention

[0004] To solve the problems of low evaluation efficiency and reliability in the existing technology, the present application provides a method and device for evaluating the voltage support strength of a grid connection system.

[0005] In a first aspect, the present application provides a method for evaluating the voltage support strength of a grid connection system, which may include:

[0006] Determine the closed-loop characteristic equation of the grid connection system according to the current transfer function of the grid connection point of the grid-connected inverter.

[0007] Calculate the critical short-circuit ratio of the grid connection point according to the closed-loop characteristic equation of the grid connection system.

[0008] Evaluate the voltage support strength of the grid connection system according to the critical short-circuit ratio of the grid connection point.

[0009] In some possible implementation manners, calculating the critical short-circuit ratio according to the closed-loop characteristic equation of the grid connection system includes:

[0010] Determine the real part equation and the imaginary part equation of the closed-loop characteristic equation according to the closed-loop characteristic equation of the grid connection system.

[0011] Use the root locus method to find the critical short-circuit ratio according to the real part equation and the imaginary part equation.

[0012] Optionally, the grid-connected inverter is a grid-forming inverter, and the current transfer function satisfies:

[0013]

[0014] The grid-connected inverter is a grid-following inverter, and the current transfer function satisfies:

[0015]

[0016] where, I o (s) represents the output current at the grid connection point. V GFM (s) represents the output voltage of the grid-connected inverter. V g (s) represents the voltage of the AC grid. Y g (s) represents the line admittance of the AC grid, and satisfies Y g (s) = Z g (s) -1 . Z g (s) represents the line impedance of the AC grid. I GFL (s) represents the output current of the grid-connected inverter. Y o (s) represents the output admittance of the grid-connected inverter, and satisfies Y o (s) = Z o (s) -1 . Z o (s) represents the output impedance of the grid-connected inverter. s represents the Laplace operator.

[0017] Exemplarily, the grid-connected inverter is a grid-forming inverter, and the closed-loop characteristic equation satisfies

[0018] 1 + Z o (s)Y g (s) = 0.

[0019] The grid-connected inverter is a grid-following inverter, and the closed-loop characteristic equation satisfies 1 + Y o (s)Z g (s) = 0.

[0020] Optionally, the impedance of the AC grid satisfies:

[0021] Z g (s) = sL g

[0022] where, L g represents the line inductance of the AC grid, and satisfies SCR represents the short-circuit ratio at the grid connection point, ω n represents the rated frequency of the grid-connected system, P dN represents the rated power of the grid-connected inverter, U NRepresents the rated line voltage of the point of common coupling.

[0023] Exemplarily, the grid-connected inverter is a grid-forming inverter, and the real part equation and the imaginary part equation satisfy:

[0024]

[0025] Among them, Z o (jb) represents the output impedance of the grid-connected inverter under the critical stable condition of the AC grid, Y g (jb,CSCR) represents the line admittance of the AC grid under the critical stable condition of the AC grid, j represents the imaginary unit, b represents the amplitude of the imaginary root of the closed-loop characteristic equation, and CSCR represents the critical short-circuit ratio of the point of common coupling.

[0026] The grid-connected inverter is a grid-following inverter, and the real part equation and the imaginary part equation satisfy:

[0027]

[0028] Among them, Y o (jb) represents the output admittance of the grid-connected inverter under the critical stable condition of the AC grid,

[0029] Z g (jb,CSCR) represents the line impedance of the AC grid under the critical stable condition of the AC grid.

[0030] In some other possible implementation manners, evaluating the voltage support strength of the grid-connected system according to the critical short-circuit ratio of the point of common coupling includes:

[0031] When the grid-connected inverter is a grid-forming inverter, when the short-circuit ratio at the point of common coupling is less than the critical short-circuit ratio, the voltage support strength of the grid-connected system meets the stability condition of the grid-connected system; conversely, the voltage support strength of the grid-connected system does not meet the stability condition of the grid-connected system.

[0032] When the grid-connected inverter is a grid-following inverter, when the short-circuit ratio at the point of common coupling is greater than the critical short-circuit ratio, the voltage support strength of the grid-connected system meets the stability condition of the grid-connected system; conversely, the voltage support strength of the grid-connected system does not meet the stability condition of the grid-connected system.

[0033] In a second aspect, the present application provides a device for evaluating the voltage support strength of a grid-connected system, which may include:

[0034] A determination module, configured to determine the closed-loop characteristic equation of the grid-connected system according to the current transfer function of the point of common coupling of the grid-connected inverter.

[0035] A calculation module, configured to calculate the critical short-circuit ratio of the point of common coupling according to the closed-loop characteristic equation of the grid-connected system.

[0036] An evaluation module for evaluating the voltage support strength of a grid-connected system according to the critical short-circuit ratio of the grid connection point.

[0037] In a possible implementation, the calculation module is specifically configured to:

[0038] Determine the real part equation and the imaginary part equation of the closed-loop characteristic equation according to the closed-loop characteristic equation of the grid-connected system.

[0039] Use the root locus method to find the critical short-circuit ratio according to the real part equation and the imaginary part equation.

[0040] Optionally, the grid-connected inverter is a grid-forming inverter, and the current transfer function satisfies:

[0041]

[0042] The grid-connected inverter is a grid-following inverter, and the current transfer function satisfies:

[0043]

[0044] Where, I o (s) represents the output current of the grid connection point. V GFM (s) represents the output voltage of the grid-connected inverter. V g (s) represents the voltage of the AC power grid. Y g (s) represents the line admittance of the AC power grid, and satisfies Y g (s) = Z g (s) -1 . Z g (s) represents the line impedance of the AC power grid. I GFL (s) represents the output current of the grid-connected inverter. Y o (s) represents the output admittance of the grid-connected inverter, and satisfies Y o (s) = Z o (s) -1 . Z o (s) represents the output impedance of the grid-connected inverter. s represents the Laplace operator.

[0045] Exemplarily, the grid-connected inverter can be a grid-forming inverter, and the closed-loop characteristic equation can satisfy 1 + Z o (s)Y g (s) = 0.

[0046] The grid-connected inverter can be a grid-following inverter, and the closed-loop characteristic equation can satisfy 1 + Y o (s)Z g (s) = 0.

[0047] The impedance of the AC power grid satisfies:

[0048] Z g(s) = sL g

[0049] wherein, L g represents the line inductance of the AC power grid, satisfying SCR represents the short - circuit ratio of the point of common coupling, ω n represents the rated frequency of the grid - connected system, P dN represents the rated power of the grid - connected inverter, U N represents the rated line voltage of the point of common coupling.

[0050] The grid - connected inverter is a grid - forming inverter, and the real - part equation and the imaginary - part equation satisfy:

[0051]

[0052] wherein, Z o (jb) represents the output impedance of the grid - connected inverter under the critical stable condition of the AC power grid,

[0053] Y g (jb, CSCR) represents the line admittance of the AC power grid under the critical stable condition of the AC power grid, j represents the imaginary unit, b represents the amplitude of the imaginary root of the closed - loop characteristic equation, and CSCR represents the critical short - circuit ratio of the point of common coupling.

[0054] The grid - connected inverter is a grid - following inverter, and the real - part equation and the imaginary - part equation satisfy:

[0055]

[0056] wherein, Y o (jb) represents the output admittance of the grid - connected inverter under the critical stable condition of the AC power grid,

[0057] Z g (jb, CSCR) represents the line impedance of the AC power grid under the critical stable condition of the AC power grid.

[0058] In another possible implementation, the evaluation module is specifically used for:

[0059] When the grid - connected inverter is a grid - forming inverter, when the short - circuit ratio of the point of common coupling is less than the critical short - circuit ratio, the voltage support strength of the grid - connected system meets the stable condition of the grid - connected system; conversely, the voltage support strength of the grid - connected system does not meet the stable condition of the grid - connected system.

[0060] When the grid - connected inverter is a grid - following inverter, when the short - circuit ratio of the point of common coupling is greater than the critical short - circuit ratio, the voltage support strength of the grid - connected system meets the stable condition of the grid - connected system; conversely, the voltage support strength of the grid - connected system does not meet the stable condition of the grid - connected system.

[0061] On the other hand, the present application also provides a computer device, including: one or more processors.

[0062] The processor is configured to execute one or more programs.

[0063] When the one or more programs are executed by the one or more processors, the evaluation method as described above is implemented.

[0064] On the other hand, the present application also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed, the evaluation method as described above is implemented.

[0065] Compared with the prior art, the beneficial effects of the present application are as follows:

[0066] In the grid-connected system voltage support strength evaluation method provided by the present application, the closed-loop characteristic equation of the grid-connected system is determined according to the current transfer function of the grid connection point, and the critical short-circuit ratio of the grid connection point is calculated according to the closed-loop characteristic equation of the grid-connected system, thereby realizing the evaluation of the voltage support strength of the grid-connected system. Compared with the related art that obtains the critical short-circuit ratio through time-domain simulation, the process of obtaining the critical short-circuit ratio in the present application is highly efficient, which can improve the evaluation efficiency of the evaluation method. Moreover, it can ensure the accuracy of the critical short-circuit ratio, thereby accurately reflecting the true voltage support strength of the grid-connected system, that is, the reliability of the evaluation method is relatively high.

[0067] The present application fully considers the influence of the output impedance of the grid-connected inverter. The obtained critical short-circuit ratio can more comprehensively reflect the voltage support strength of the grid-connected system containing power electronic devices such as new energy and energy storage, overcoming the drawback in the related art that the influence of the inverters of new energy, energy storage, etc. on the voltage support strength of the AC power grid cannot be reflected, and providing an important theoretical basis for the stable operation of the grid-connected system.

[0068] The present application uses the root locus method to solve the real part equation and the imaginary part equation of the closed-loop characteristic equation, realizing the accurate calculation of the critical short-circuit ratio. Compared with continuously adjusting parameters in the related art, the present application improves the calculation efficiency of the critical short-circuit ratio.

[0069] The present application calculates the critical short-circuit ratio by solving the closed-loop characteristic equation of the grid-connected system. Compared with obtaining the critical short-circuit ratio by the method of gradual approximation in the related art, the calculation accuracy of the critical short-circuit ratio is improved, providing a reliable basis for evaluating the voltage support strength of the grid-connected system.

[0070] The present application fully considers the impedance characteristic differences between the grid-following inverter and the grid-forming inverter. The calculation of the critical short-circuit ratio takes into account the output impedance of the grid-connected inverter, can accurately quantify the influence of different control methods on the voltage support strength of the grid-connected system, and can more comprehensively evaluate the voltage support strength of the grid-connected system. Description of the Drawings

[0071] To more clearly illustrate the technical solutions in the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0072] Figure 1 Schematic connection diagram of the grid-connected inverter and the AC power grid in the embodiment of the present application;

[0073] Figure 2 Schematic flowchart of a method for evaluating the voltage support strength of the grid-connected system in the embodiment of the present application;

[0074] Figure 3a Schematic structural diagram of a small-signal model of the grid-forming inverter in the embodiment of the present application;

[0075] Figure 3b Schematic structural diagram of a small-signal model of the grid-following inverter in the embodiment of the present application;

[0076] Figure 4a Schematic diagram of the active power waveform output after the grid-forming inverter in the embodiment of the present application is connected to power grids with different strengths;

[0077] Figure 4b Schematic diagram of the active power waveform output after the grid-following inverter in the embodiment of the present application is connected to power grids with different strengths;

[0078] Figure 5 Schematic structural diagram of a device for evaluating the voltage support strength of the grid-connected system in the embodiment of the present application. Detailed implementation manners

[0079] The following will describe the technical solutions in the present application in conjunction with the drawings.

[0080] The terms "first", "second", etc. in the embodiments of the specification, claims and drawings of the present application are only used for the purpose of distinguishing descriptions, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying order. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a method, system, product or device including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0081] It should be understood that in this application, "at least one (item)" means one or more, and "a plurality" means two or more. "And / or" is used to describe the association relationship of associated objects and indicates that three relationships can exist. For example, "A and / or B" can mean: only A exists, only B exists, and both A and B exist at the same time. Among them, A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one (one) of the following" or similar expressions refer to any combination of these items, including any combination of single items (one) or plural items (ones). For example, at least one (one) of a, b, or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0082] Embodiment 1:

[0083] The embodiment of this application provides a method for evaluating the voltage support strength of a grid-connected system. The grid-connected system may include a grid-connected inverter 1. The grid-connected inverter 1 may be a grid-forming inverter or a grid-following inverter. The connection schematic diagram of the grid-connected inverter 1 and the AC power grid 2 is as Figure 1 shown. Figure 1 In, A represents a grid-forming inverter, and B represents a grid-following inverter. Z o (s) represents the output impedance of the grid-connected inverter 1, and Y o (s) represents the output admittance of the grid-connected inverter 1, and V GFM (s) represents the output voltage of the grid-connected inverter 1, and I GFL (s) represents the output current of the grid-connected inverter 1, and I o (s) represents the output current of the grid connection point, and U o (s) represents the voltage of the grid connection point, and Z g (s) represents the line impedance of the AC power grid 2, and V g (s) represents the voltage of the AC power grid 2.

[0084] As Figure 2 shown, the evaluation method 100 includes the following steps:

[0085] Step S1: Determine the closed-loop characteristic equation of the grid-connected system according to the current transfer function of the grid connection point of the grid-connected inverter.

[0086] Step S2: Calculate the critical short-circuit ratio of the grid connection point according to the closed-loop characteristic equation of the grid-connected system.

[0087] Step S3: Evaluate the voltage support strength of the grid-connected system according to the critical short-circuit ratio of the grid connection point.

[0088] In some embodiments, according to Figure 3aThe small-signal model of the grid-forming inverter is shown. The current transfer function of the grid connection point of the grid-forming inverter can satisfy:

[0089]

[0090] According to Figure 3b The small-signal model of the grid-following inverter is shown. The current transfer function of the grid connection point of the grid-following inverter can satisfy:

[0091]

[0092] Among them, I o (s) represents the output current of the grid connection point. V GFM (s) represents the output voltage of the grid-connected inverter. V g (s) represents the voltage of the AC power grid. Y g (s) represents the line admittance of the AC power grid, and satisfies Y g (s) = Z g (s) -1 . Z g (s) represents the line impedance of the AC power grid. I GFL (s) represents the output current of the grid-connected inverter. Y o (s) represents the output admittance of the grid-connected inverter, and satisfies Y o (s) = Z o (s) -1 . Z o (s) represents the output impedance of the grid-connected inverter. s represents the Laplace operator.

[0093] The grid-connected inverter is a grid-forming inverter, and the closed-loop characteristic equation satisfies 1 + Z o (s)Y g (s) = 0.

[0094] The grid-connected inverter is a grid-following inverter, and the closed-loop characteristic equation satisfies 1 + Y o (s)Z g (s) = 0.

[0095] Optionally, the impedance of the AC power grid satisfies:

[0096] Z g (s) = sL g

[0097] Among them, L g represents the line inductance of the AC power grid, and satisfies SCR represents the short-circuit ratio of the grid connection point, ω n represents the rated frequency of the grid-connected system, P dN represents the rated power of the grid-connected inverter, U N represents the rated line voltage of the grid connection point.

[0098] In some other embodiments, calculating the critical short - circuit ratio according to the closed - loop characteristic equation of the grid - connected system in step S2 includes:

[0099] Determining the real - part equation and the imaginary - part equation of the closed - loop characteristic equation according to the closed - loop characteristic equation of the grid - connected system.

[0100] Using the root - locus method to find the critical short - circuit ratio according to the real - part equation and the imaginary - part equation.

[0101] Exemplarily, for a grid - forming inverter, the real - part equation and the imaginary - part equation satisfy:

[0102]

[0103] where Z o (jb) represents the output impedance of the grid - connected inverter under the condition of critical stability of the AC power grid,

[0104] Y g (jb, CSCR) represents the line admittance of the AC power grid under the condition of critical stability of the AC power grid, j represents the imaginary unit, b represents the amplitude of the imaginary root of the closed - loop characteristic equation, and CSCR represents the critical short - circuit ratio at the grid - connection point.

[0105] For a grid - following inverter, the real - part equation and the imaginary - part equation satisfy:

[0106]

[0107] where Y o (jb) represents the output admittance of the grid - connected inverter under the condition of critical stability of the AC power grid, Z g (jb, CSCR) represents the line impedance of the AC power grid under the condition of critical stability of the AC power grid.

[0108] In still some other embodiments, evaluating the voltage support strength of the grid - connected system according to the critical short - circuit ratio at the grid - connection point in step S3 includes:

[0109] (1) For a grid - forming inverter, when the short - circuit ratio at the grid - connection point is less than the critical short - circuit ratio, the voltage support strength of the grid - connected system meets the stability conditions of the grid - connected system; conversely, the voltage support strength of the grid - connected system does not meet the stability conditions of the grid - connected system.

[0110] (2) For a grid - following inverter, when the short - circuit ratio at the grid - connection point is greater than the critical short - circuit ratio, the voltage support strength of the grid - connected system meets the stability conditions of the grid - connected system; conversely, the voltage support strength of the grid - connected system does not meet the stability conditions of the grid - connected system.

[0111] The effectiveness and accuracy of the method for evaluating the voltage support strength of the grid-connected system in the embodiments of this application are verified through simulation, and the schematic diagram of the active power waveform output after the grid-forming inverter is connected to power grids with different strengths as shown in Figure 4a and the schematic diagram of the active power waveform output after the grid-following inverter is connected to power grids with different strengths as shown in Figure 4b are obtained. Figure 4a In Figure 4b and

[0112] Figure 4a , the vertical coordinate represents the active power P output after the grid-forming inverter / grid-following inverter is connected to power grids with different strengths, and the horizontal coordinate represents time t.

[0113] Figure 4b In

[0114] , the calculated critical short-circuit ratio CSCR can be 6.38. When the grid-forming inverter is connected to a relatively weak AC grid, SCR = 6.13. Since CSCR > SCR, it can be determined that the voltage support strength of the grid-connected system meets the stability conditions of the grid-connected system, that is, the grid-connected system can operate stably. When the grid-forming inverter is connected to a relatively strong AC grid, CSCR < SCR, it can be determined that the voltage support strength of the grid-connected system does not meet the stability conditions of the grid-connected system, that is, the grid-connected system cannot operate stably.

[0115] In Figure 5 , the calculated critical short-circuit ratio CSCR is 2.30. When the grid-following inverter is connected to a relatively weak AC grid, SCR = 2.19. Since CSCR > SCR, it can be determined that the voltage support strength of the grid-connected system does not meet the stability conditions of the grid-connected system, that is, the grid-connected system cannot operate stably. When the grid-following inverter is connected to a relatively strong AC grid, SCR = 2.41. Since CSCR < SCR, it can be determined that the voltage support strength of the grid-connected system meets the stability conditions of the grid-connected system, that is, the grid-connected system can operate stably.

[0116] Example 2:

[0117] Based on the same inventive concept, the embodiments of this application further provide an apparatus for evaluating the voltage support strength of a grid-connected system. As shown in

[0118] , the evaluation apparatus 200 may include:

[0119] A determination module 201, configured to determine the closed-loop characteristic equation of the grid-connected system according to the current transfer function at the connection point of the grid-connected inverter.

[0120] Determine the real - part equation and the imaginary - part equation of the closed - loop characteristic equation according to the closed - loop characteristic equation of the grid - connected system.

[0121] According to the real - part equation and the imaginary - part equation, use the root - locus method to find the critical short - circuit ratio.

[0122] Optionally, the grid - connected inverter is a grid - forming inverter, and the current transfer function satisfies:

[0123]

[0124] The grid - connected inverter is a grid - following inverter, and the current transfer function satisfies:

[0125]

[0126] Among them, I o (s) represents the output current of the grid - connection point. V GFM (s) represents the output voltage of the grid - connected inverter. V g (s) represents the voltage of the AC power grid. Y g (s) represents the line admittance of the AC power grid, and satisfies Y g (s)=Z g (s) -1 . Z g (s) represents the line impedance of the AC power grid. I GFL (s) represents the output current of the grid - connected inverter. Y o (s) represents the output admittance of the grid - connected inverter, and satisfies Y o (s)=Z o (s) -1 . Z o (s) represents the output impedance of the grid - connected inverter. s represents the Laplace operator.

[0127] Exemplarily, the grid - connected inverter can be a grid - forming inverter, and the closed - loop characteristic equation can satisfy 1 + Z o (s)Y g (s)=0.

[0128] The grid - connected inverter can be a grid - following inverter, and the closed - loop characteristic equation can satisfy 1 + Y o (s)Z g (s)=0.

[0129] The impedance of the AC power grid satisfies:

[0130] Z g (s)=sL g

[0131] Among them, L g represents the line inductance of the AC power grid, and satisfies The SCR represents the short - circuit ratio of the grid - connection point, ω n represents the rated frequency of the grid - connected system, P dN represents the rated power of the grid - connected inverter, U N represents the rated line voltage of the grid - connection point.

[0132] The grid - connected inverter is a grid - forming inverter, and the real - part equation and the imaginary - part equation satisfy:

[0133]

[0134] Among them, Z o (jb) represents the output impedance of the grid - connected inverter under the critical stable condition of the AC power grid,

[0135] Y g (jb, CSCR) represents the line admittance of the AC power grid under the critical stable condition of the AC power grid, j represents the imaginary unit, b represents the amplitude of the imaginary root of the closed - loop characteristic equation, and CSCR represents the critical short - circuit ratio of the grid - connection point.

[0136] The grid - connected inverter is a grid - following inverter, and the real - part equation and the imaginary - part equation satisfy:

[0137]

[0138] Among them, Y o (jb) represents the output admittance of the grid - connected inverter under the critical stable condition of the AC power grid,

[0139] Z g (jb, CSCR) represents the line impedance of the AC power grid under the critical stable condition of the AC power grid.

[0140] In another possible implementation, the evaluation module 203 is specifically used for:

[0141] When the grid - connected inverter is a grid - forming inverter, when the short - circuit ratio of the grid - connection point is less than the critical short - circuit ratio, the voltage support strength of the grid - connected system meets the stable condition of the grid - connected system; conversely, the voltage support strength of the grid - connected system does not meet the stable condition of the grid - connected system.

[0142] When the grid - connected inverter is a grid - following inverter, when the short - circuit ratio of the grid - connection point is greater than the critical short - circuit ratio, the voltage support strength of the grid - connected system meets the stable condition of the grid - connected system; conversely, the voltage support strength of the grid - connected system does not meet the stable condition of the grid - connected system.

[0143] Embodiment 3:

[0144] Based on the same inventive concept, an embodiment of the present application further provides a computer device, which includes a processor and a memory. The memory is used to store a computer program, and the computer program includes program instructions. The processor is used to execute the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or may also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, and is suitable for implementing one or more instructions. Specifically, it is suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of the evaluation method provided in the above embodiment.

[0145] Embodiment 4:

[0146] Based on the same inventive concept, an embodiment of the present application further provides a computer-readable storage medium, specifically a computer-readable storage medium (Memory). The computer-readable storage medium is a memory device in the computer device and is used to store programs and data. It can be understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and, of course, the extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space, and the operating system of the terminal is stored in this storage space. And, one or more instructions suitable for being loaded and executed by the processor are also stored in this storage space. These instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The one or more instructions stored in the computer-readable storage medium can be loaded and executed by the processor to implement the steps of the evaluation method provided in the above embodiment.

[0147] Those skilled in the art should understand that the embodiments of the application can be provided as a method, a system, or a computer program product. Therefore, the application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) that contain computer-usable program code.

[0148] The application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the application. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0149] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0150] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0151] The above are only embodiments of the application and are not used to limit the application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the application are included in the scope of the claims of the pending application for the invention.

Claims

1. A method for evaluating the voltage support strength of a grid-connected system, characterized in that, Including: Determine the closed-loop characteristic equation of the grid-connected system according to the current transfer function of the grid connection point of the grid-connected inverter; Calculate the critical short-circuit ratio of the grid connection point according to the closed-loop characteristic equation of the grid-connected system; Evaluate the voltage support strength of the grid-connected system according to the critical short-circuit ratio of the grid connection point.

2. The evaluation method according to claim 1, wherein The calculating the critical short-circuit ratio according to the closed-loop characteristic equation of the grid-connected system includes: Determine the real part equation and the imaginary part equation of the closed-loop characteristic equation according to the closed-loop characteristic equation of the grid-connected system; Use the root locus method to find the critical short-circuit ratio according to the real part equation and the imaginary part equation.

3. The evaluation method according to claim 1, wherein The grid-connected inverter is a grid-forming inverter, and the current transfer function satisfies: The grid-connected inverter is a grid-following inverter, and the current transfer function satisfies: Among them, I o (s) represents the output current of the grid connection point; V GFM (s) represents the output voltage of the grid-connected inverter; V g (s) represents the voltage of the AC grid; Y g (s) represents the line admittance of the AC grid, satisfying Y g (s) = Z g (s) -1 ; Z g (s) represents the line impedance of the AC grid; I GFL (s) represents the output current of the grid-connected inverter; Y o (s) represents the output admittance of the grid-connected inverter, satisfying Y o (s) = Z o (s) -1 ; Z o (s) represents the output impedance of the grid-connected inverter; s represents the Laplace operator.

4. The evaluation method according to claim 3, wherein The grid-connected inverter is a grid-forming inverter, and the closed-loop characteristic equation satisfies 1 + Z o (s)Y g (s) = 0; The grid-connected inverter is a grid-following inverter, and the closed-loop characteristic equation satisfies 1 + Y o (s)Z g (s) = 0.

5. The evaluation method according to claim 3 or 4, characterized in that The impedance of the AC power grid satisfies: Z g (s) = sL g Among them, L g represents the line inductance of the AC power grid, satisfying SCR represents the short-circuit ratio of the grid connection point, ω n represents the rated frequency of the grid-connected system, P dN represents the rated power of the grid-connected inverter, U N represents the rated line voltage of the grid connection point.

6. The evaluation method according to claim 1, wherein The grid-connected inverter is a grid-forming inverter, and the real part equation and the imaginary part equation satisfy: Among them, Z o (jb) represents the output impedance of the grid-connected inverter under the critical stable condition of the AC power grid, Y g (jb, CSCR) represents the line admittance of the AC power grid under the critical stable condition of the AC power grid, j represents the imaginary unit, b represents the amplitude of the imaginary root of the closed-loop characteristic equation, and CSCR represents the critical short-circuit ratio of the grid connection point; The grid-connected inverter is a grid-following inverter, and the real part equation and the imaginary part equation satisfy: Among them, Y o (jb) represents the output admittance of the grid-connected inverter under the critical stable condition of the AC power grid, and Z g (jb, CSCR) represents the line impedance of the AC power grid under the critical stable condition of the AC power grid.

7. The evaluation method according to claim 1, wherein The evaluating the voltage support strength of the grid-connected system according to the critical short-circuit ratio of the grid connection point includes: When the grid-connected inverter is a grid-forming inverter, if the short-circuit ratio of the grid connection point is less than the critical short-circuit ratio, the voltage support strength of the grid-connected system meets the stability condition of the grid-connected system; otherwise, the voltage support strength of the grid-connected system does not meet the stability condition of the grid-connected system; When the grid-connected inverter is a grid-following inverter, if the short-circuit ratio of the grid connection point is greater than the critical short-circuit ratio, the voltage support strength of the grid-connected system meets the stability condition of the grid-connected system; otherwise, the voltage support strength of the grid-connected system does not meet the stability condition of the grid-connected system.

8. An evaluation device for the voltage support strength of a grid-connected system, characterized in that, Including: A determination module for determining the closed-loop characteristic equation of the grid-connected system according to the current transfer function of the grid connection point of the grid-connected inverter; A calculation module for calculating the critical short-circuit ratio of the grid connection point according to the closed-loop characteristic equation of the grid-connected system; An evaluation module for evaluating the voltage support strength of the grid-connected system according to the critical short-circuit ratio of the grid connection point.

9. The evaluation device according to claim 8, characterized in that The calculation module is specifically used for: Determine the real part equation and the imaginary part equation of the closed-loop characteristic equation according to the closed-loop characteristic equation of the grid-connected system; Use the root locus method to find the critical short-circuit ratio according to the real part equation and the imaginary part equation.

10. The evaluation device according to claim 8, characterized in that, The grid-connected inverter is a grid-forming inverter, and the current transfer function satisfies: The grid-connected inverter is a grid-following inverter, and the current transfer function satisfies: Wherein, I o (s) represents the output current of the grid connection point; V GFM (s) represents the output voltage of the grid-connected inverter; V g (s) represents the voltage of the AC power grid; Y g (s) represents the line admittance of the AC power grid, satisfying Y g (s)=Z g (s) -1 ; Z g (s) represents the line impedance of the AC power grid; I GFL (s) represents the output current of the grid-connected inverter; Y o (s) represents the output admittance of the grid-connected inverter, satisfying Y o (s)=Z o (s) -1 ; Z o (s) represents the output impedance of the grid-connected inverter; s represents the Laplace operator.

11. The evaluation device according to claim 10, wherein The grid-connected inverter is a grid-forming inverter, and the closed-loop characteristic equation satisfies 1 + Z o (s)Y g (s) = 0; The grid-connected inverter is a grid-following inverter, and the closed-loop characteristic equation satisfies 1 + Y o (s)Z g (s) = 0.

12. The evaluation device according to claim 10 or 11, characterized in that, The impedance of the AC power grid satisfies: Z g (s) = sL g Among them, L g represents the line inductance of the AC power grid, satisfying SCR represents the short-circuit ratio of the grid connection point, ω n represents the rated frequency of the grid-connected system, P dN represents the rated power of the grid-connected inverter, U N represents the rated line voltage of the grid connection point.

13. The evaluation device according to claim 8, wherein The grid-connected inverter is a grid-forming inverter, and the real part equation and the imaginary part equation satisfy: Among them, Z o (jb) represents the output impedance of the grid-connected inverter under the critical stable condition of the AC grid, Y g (jb, CSCR) represents the line admittance of the AC grid under the critical stable condition of the AC grid, j represents the imaginary unit, b represents the amplitude of the imaginary root of the closed-loop characteristic equation, and CSCR represents the critical short-circuit ratio of the grid connection point; The grid-connected inverter is a grid-following inverter, and the real part equation and the imaginary part equation satisfy: Among them, Y o (jb) represents the output admittance of the grid-connected inverter under the critical stability condition of the AC grid, and Z g (jb, CSCR) represents the line impedance of the AC grid under the critical stability condition of the AC grid.

14. The evaluation device according to claim 8, characterized in that, The evaluation module is specifically used for: The grid-connected inverter is a grid-forming inverter. When the short-circuit ratio at the point of common coupling is less than the critical short-circuit ratio, the voltage support strength of the grid-connected system meets the stability conditions of the grid-connected system; otherwise, the voltage support strength of the grid-connected system does not meet the stability conditions of the grid-connected system. The grid-connected inverter is a grid-following inverter. When the short-circuit ratio at the point of common coupling is greater than the critical short-circuit ratio, the voltage support strength of the grid-connected system meets the stability conditions of the grid-connected system; otherwise, the voltage support strength of the grid-connected system does not meet the stability conditions of the grid-connected system.

15. A computer device, characterized in that, Comprising: One or more processors; The processor is configured to store one or more programs; When the one or more programs are executed by the one or more processors, the evaluation method according to any one of claims 1 to 7 is implemented.

16. A computer-readable storage medium, characterized in that, A computer program is stored thereon, and when the computer program is executed, the evaluation method according to any one of claims 1 to 7 is implemented.

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