A method, system, device, medium and product for calculating stability margin of a multi-machine grid-connected system

Abstract

The application discloses a kind of stable margin calculation method, system, equipment, medium and product of multi-machine grid-connected system, involve stable margin calculation field, this method includes: establishing the closed-loop model of multi-machine grid-connected system of multiple phase-locked loop converter access power system;The closed-loop model of multi-machine grid-connected system includes external small signal model and internal small signal model;The isomorphic multi-machine grid-connected system of the closed-loop model of multi-machine grid-connected system is constructed;The isomorphic multi-machine grid-connected system is decoupled into multiple single-converter grid-connected subsystems;Based on generalized short-circuit ratio, the stable margin of each single-converter grid-connected subsystem is calculated, and the stable margin of multi-machine grid-connected system is determined, the stable margin of multi-machine grid-connected system can be accurately calculated by the application.

Description

Technical Field

[0001] This application relates to the field of stability margin calculation, and in particular to a method, system, device, medium and product for calculating the stability margin of a multi-machine grid-connected system. Background Technology

[0002] With the continuous advancement of dual-carbon goals, vigorously developing clean energy represented by wind power and photovoltaics has become an inevitable choice for global energy transformation. According to the International Renewable Energy Agency (IRENA), by 2050, global renewable energy consumption will account for 66% of total consumption, and renewable energy power generation will account for 86% of total electricity generation. New energy sources, represented by wind and solar power, are connected to the power system through converters. Meanwhile, frequency converter-driven loads and the rapidly developing electric vehicles also largely use power electronic devices as interfaces for grid connection. Against this backdrop, China's power system will gradually evolve into a dual-high-proportion power system of new energy and power electronic devices.

[0003] Power electronic equipment differs significantly from traditional generators in physical characteristics, control structures, and operating properties. These differences profoundly alter the dynamic behavior of power systems and greatly affect system stability, posing a significant threat to the safe and economical operation of power systems. For example, in July 2015, a severe synchronous oscillation accident involving a wind power cluster occurred in a certain region, causing a sharp drop in the temporary power output of power plant units and ultra-high voltage direct current (UHVDC) transmission. This oscillation stability problem caused by power electronic equipment severely restricts the grid's ability to absorb new energy sources. However, the mechanisms of some oscillation events have not yet been fully elucidated, and the impact of oscillations on system safety and stability cannot be accurately quantified. Oscillation accidents still occur frequently.

[0004] Unlike the shaft torsional vibration of synchronous machines and the electrical resonance formed by inductors and capacitors in the power grid in traditional power systems, the oscillations in renewable energy grid-connected systems originate from coupled oscillations generated by the interaction between power electronic devices or between them and the AC grid, representing a new type of oscillation. Because the stability mechanisms of traditional power systems and power electronic devices are inconsistent, traditional analytical methods based on synchronous machines are difficult to apply. Therefore, analyzing the dynamic coupling relationships in renewable energy power systems, studying the grid-connected stability of large-scale power electronic devices, and revealing the stability mechanism of converters are fundamental to ensuring the safe and stable operation of modern power systems.

[0005] However, due to the high degree of nonlinearity in the stability margin of oscillations caused by power electronic equipment, dynamic modeling of the power system and modeling of the internal control methods of the converter are often involved, making quantitative solutions difficult. Therefore, the mechanism of oscillation is often revealed through single-unit grid-connected models, and relatively mature methods such as small-signal analysis and impedance analysis have been developed for quantifying the stability margin of single-unit grid-connected models. However, actual power systems are often not single-unit systems, but multi-infeed systems with multiple renewable energy power plants connected to them. The approach and methods of single-unit grid connection are difficult to apply to multi-infeed systems. Summary of the Invention

[0006] The purpose of this application is to provide a method, system, device, medium, and product for calculating the stability margin of a multi-machine grid-connected system, which can accurately calculate the stability margin of the multi-machine grid-connected system.

[0007] To achieve the above objectives, this application provides the following solution: Firstly, this application provides a method for calculating the stability margin of a multi-machine grid-connected system, including: A closed-loop model of a multi-machine grid-connected system with multiple phase-locked loop converters connected to the power system is established; the closed-loop model of the multi-machine grid-connected system includes an external small-signal model and an internal small-signal model. Construct a closed-loop model of the aforementioned multi-machine grid-connected system; The homogeneous multi-machine grid-connected system is decoupled into multiple single-converter grid-connected subsystems; Based on the generalized short-circuit ratio, the stability margin of each single-converter grid-connected subsystem is calculated, and the stability margin of the multi-machine grid-connected system is determined.

[0008] Secondly, this application provides a stability margin calculation system for a multi-machine grid-connected system, comprising: The multi-machine grid-connected system closed-loop model establishment module is used to establish a closed-loop model of a multi-machine grid-connected system with multiple phase-locked loop converters connected to the power system; the multi-machine grid-connected system closed-loop model includes an external small-signal model and an internal small-signal model. A homogeneous multi-machine grid-connected system construction module is used to construct the homogeneous multi-machine grid-connected system of the closed-loop model of the multi-machine grid-connected system. The decoupling module is used to decouple the homogeneous multi-machine grid-connected system into multiple single-converter grid-connected subsystems; The stability margin calculation module is used to calculate the stability margin of each single-converter grid-connected subsystem based on the generalized short-circuit ratio, and to determine the stability margin of the multi-machine grid-connected system.

[0009] Thirdly, this application provides a computer device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the above-described method for calculating the stability margin of a multi-machine grid-connected system.

[0010] Fourthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described method for calculating the stability margin of a multi-machine grid-connected system.

[0011] Fifthly, this application provides a computer program product, including a computer program that, when executed by a processor, implements the above-described method for calculating the stability margin of a multi-machine grid-connected system.

[0012] According to the specific embodiments provided in this application, this application has the following technical effects: This application establishes a closed-loop model of a multi-machine grid-connected system with multiple phase-locked loop converters connected to the power system. This closed-loop model includes an external small-signal model and an internal small-signal model, thereby analyzing the coupling relationship between the internal and external converters in the multi-machine grid-connected system. Since the closed-loop model of the multi-machine grid-connected system cannot be directly decoupled, this application constructs a homogeneous multi-machine grid-connected system based on the closed-loop model of the multi-machine grid-connected system, decoupling the homogeneous multi-machine grid-connected system into multiple single-converter grid-connected subsystems, thereby achieving decoupling of the closed-loop model of the multi-machine grid-connected system. Finally, based on the generalized short-circuit ratio, the stability margin of each single-converter grid-connected subsystem is calculated to accurately calculate the oscillation margin of the multi-machine grid-connected system. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments 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.

[0014] Figure 1 A flowchart illustrating a method for calculating the stability margin of a multi-machine grid-connected system according to an embodiment of this application; Figure 2 A schematic diagram of a new energy power system with multiple converters connected to the grid, provided as an embodiment of this application; Figure 3 This is a schematic diagram illustrating the relationship between local and global coordinates of a converter, provided in an embodiment of this application. Figure 4 This is a schematic diagram of a closed-loop model of a multi-machine grid-connected system provided in an embodiment of this application; Figure 5 This is a schematic diagram illustrating the relationship between short-circuit ratio and stability margin according to an embodiment of this application. Detailed Implementation

[0015] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0016] To make the objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] like Figure 1 As shown in the figure, this application provides a method for calculating the stability margin of a multi-machine grid-connected system, including: S1: Establish a closed-loop model of a multi-machine grid-connected system with multiple phase-locked loop converters connected to the power system; the closed-loop model of the multi-machine grid-connected system includes an external small-signal model and an internal small-signal model.

[0018] S2: Construct the isomorphic multi-machine grid-connected system of the closed-loop model of the multi-machine grid-connected system.

[0019] S3: Decouple the homogeneous multi-machine grid-connected system into multiple single-converter grid-connected subsystems.

[0020] S4: Based on the generalized short-circuit ratio, calculate the stability margin of each single-converter grid-connected subsystem and determine the stability margin of the multi-machine grid-connected system.

[0021] In an exemplary embodiment, S1 specifically includes: S11: For any line with an adjacent passive node in a new energy power system with multiple converters connected to the grid, determine the dynamic equations according to the impedance method.

[0022] S12: With the current injection disturbance of the passive node being 0, the admittance matrix after node compression is determined by eliminating the internal nodes according to Kron's order reduction.

[0023] S13: Determine the dynamic behavior of the converter injecting into the AC grid based on the admittance matrix and the dynamic equation; the dynamic behavior of the converter injecting into the AC grid is an external small-signal model.

[0024] S14: Based on the relationship between the local coordinate system and the global rotating coordinate system of each converter in a multi-machine grid-connected system, determine the dynamic equation of any converter in the global rotating coordinate system.

[0025] S15: Based on the dynamic equations of any converter in the global rotating coordinate system, extend the internal small-signal model of the entire multi-machine grid-connected system.

[0026] In practical applications, (1) the external small signal model is established as follows.

[0027] Consider as Figure 2 The illustrated new energy power system consists of n converters coupled through an AC network and connected to an infinite AC power grid. Nodes 1 to n are converter nodes, and nodes n+1 to n+m are internal passive nodes (nodes not connected to the converters). The AC power grid is represented by the (n+m+1)th node, which can be considered an infinite bus. Establishment... Figure 2 The closed-loop dynamic model establishes the dynamic relationship between the small disturbances of the voltage at each node and the power flow of the entire system, as shown in Equation (1). This provides a basis for the establishment of multi-machine grid-connected systems and the calculation of small disturbance stability margins in multi-machine grid-connected systems.

[0028] (1) This represents the change in node current inflow. Let A be the node voltage change and A be the node admittance matrix.

[0029] This application uses the impedance method to calculate the model.

[0030] For any line ij with adjacent passive nodes, its dynamic equation can be expressed as equation (2) according to impedance analysis.

[0031] (2) in, The current flowing from node i to node j is ( (Indicates the amount of disturbance). It is the voltage of node i (global). (in coordinate system) It is the susceptance between node i and node j. This refers to the R / L ratio of the circuit. Under the same voltage level, the R / L values ​​do not differ significantly, so it can be assumed that all circuits... They are all equal. F(s) is the dynamic characteristic of the converter.

[0032] Since this application addresses the small-disturbance stability problem, the voltage of the infinite bus can be considered constant. When forming the admittance matrix of the power grid, it can be treated as a grounding node, denoted as... Let be the admittance matrix of the system, whose elements satisfy (3): (3) Since the current injection disturbance of the passive node is 0, the internal node can be eliminated by Kron reduction without affecting the small disturbance stability of the system, thus obtaining the admittance matrix after node compression as (4): (4) in, , , , All are submatrices of Q, satisfying Q= .

[0033] Then, by combining (2) and (4), we can obtain the dynamic behavior of the converter injected into the AC grid, i.e., the external small-signal model: (5) in, It is the current injected into the AC power grid by n converters. It is the voltage vector of the converter. Represents the Kronecker product of matrices; Let i be the direct-axis current value injected into the AC grid for the i-th converter. The quadrature-axis current value injected into the AC grid for the i-th converter. Let i be the direct-axis voltage value of the i-th converter. Let be the quadrature-axis voltage value of the i-th converter.

[0034] (2) Establishment of internal small signal model.

[0035] Considering that the converter adopts constant active power-reactive power control, and the outer loop transfer functions of both the active and reactive power loops are the same, based on current research, there is a definite calculation method for the admittance model of the i-th converter, denoted as . .

[0036] The relationship between the local coordinate system and the global rotating coordinate system of each converter in a multi-machine grid-connected system is as follows: Figure 3 As shown, the indigenous Let be the local coordinate system of the i-th converter, with a rotational angular frequency of . The angle between it and the global coordinate system is When equal to the steady-state equilibrium point, the first The angle between the bus voltages of the converter.

[0037] according to Figure 3 The relationship in the system, the first The dynamic equation of the converter in the global coordinate system can be expressed as (6): (6) in, , It is the capacity factor of the i-th converter, which is the ratio of the rated capacity to the per-unit capacity of the converter.

[0038] As can be seen from equation (6), the dynamic model of the i-th converter is only related to the state variables of the i-th device. Therefore, equation (6) of the small signal of a single converter can be extended to the internal small signal model (7) of the entire system: (7) in, This represents a diagonal block matrix consisting of the converter admittance matrices. The capacity coefficient of the i-th converter; Here is the complex frequency domain expression for the admittance of the i-th converter; Let be the complex frequency domain d-axis expression for the admittance of the i-th converter; Let be the complex frequency domain q-axis expression for the admittance of the i-th converter.

[0039] Based on (5) and (7), a closed-loop model of a multi-machine grid-connected system can be obtained, such as... Figure 4 As shown, the open-loop transfer function of this system can be expressed as: The generalized Nyquist criterion can be used to determine the stability of the system using L(s), but it cannot quantitatively characterize the system's stability margin or describe the impact of each converter on the system's stability.

[0040] Based on S1, quantitative small-disturbance stability calculations are performed for the isomorphic converter equipment in the system.

[0041] In an exemplary embodiment, S2 specifically includes: This application targets a homogeneous multi-machine grid-connected system, which satisfies the assumption that: in steady state, the power on the interconnects between converter devices is much less than its transmission limit, i.e., the steady-state phase angle of the converter bus satisfies... The converters in the system are "similar", meaning that the controller parameters, output power, power factor, and per-unit values ​​of the main circuit parameters based on the device's own capacity are all the same.

[0042] Under the isomorphism assumption, the expressions for the admittance matrices of each converter are identical in local coordinates, and since the power on the tie line is much smaller than the transmission limit, therefore... If this holds true, then equation (7) can be rewritten as: (8) In the formula, The characteristic equation of the new energy power system can then be expressed as: (9) This expression is equivalent to: (10) In the formula, It is an identity matrix. Note that... It is a weighted Laplacian matrix composed of the capacity ratio matrix and the network admittance matrix. It is a positive definite matrix, and there exists an invertible matrix W such that... Diagonalization: (11) in, For matrix n eigenvalues.

[0043] In an exemplary embodiment, S3 specifically includes: substituting (11) into (10) yields: (12) in, for...; This is the admittance matrix of the converter.

[0044] The above equation shows that a homogeneous multi-machine grid-connected system can be decoupled into n independent single-converter grid-connected subsystems, each of which is connected to a converter with a short-circuit ratio of... It consists of a single-machine infinite system.

[0045] In an exemplary embodiment, S4 specifically includes: From S3, we can see that a multi-machine grid-connected system can be transformed into the analysis of several single-converter grid-connected subsystems. For each decoupled single-converter grid-connected subsystem, there is already considerable research available, enabling the deriving of the open-loop transfer function for the stability of the single-machine system. The derivation will not be elaborated here, but is denoted as... .

[0046] The steps for determining the stability margin are: (1) Calculate the equivalent short-circuit ratio of the single-unit system; (2) Calculate the sensitivity norm defined in this paper for the weakest single-unit system. The equivalent short-circuit ratio is easy to calculate, but it can only determine the relative stability of the system. The larger the equivalent short-circuit ratio, the stronger and more stable the system is, but it cannot accurately calculate the distance between the system and the critical stability state. Based on the rule that the smaller the short-circuit ratio of the AC power grid, the smaller the stability margin of the grid-connected system with the grid-type converter, this application defines the stability margin of the i-th single-converter grid-connected subsystem as expressed by the sensitivity. Norm representation, as in equation (13): (13) according to The meaning of norm, express Nyquist curve to Distance between points For the stability margin of the converter grid-connected subsystem, The larger the value, the smaller the system stability margin.

[0047] Simulation results have verified the short-circuit ratio in a single-machine system. The relationship with stability margin is as follows Figure 5 As shown, it can be seen that the stability margin of the system increases with... Monotonically increasing. Therefore, the small-disturbance stability of a multi-machine grid-connected system is determined by the weakest equivalent single-machine system in equation (13) (i.e., the short-circuit ratio is). (System). Defined as the generalized short-circuit ratio of a new energy power system, denoted as That is, the generalized short-circuit ratio is a matrix. The minimum eigenvalue. Although the generalized short-circuit ratio cannot quantitatively characterize the distance from the instability point, in the same system, nodes with smaller generalized short-circuit ratios are more prone to instability. Therefore, the calculation of the stability margin in a homogeneous multi-machine grid-connected system is to first find the weakest node based on the generalized short-circuit ratio, and then calculate the stability margin of that node according to equation (13). As a stability margin for multi-machine grid-connected systems.

[0048] This application provides a stability margin calculation system for a multi-machine grid-connected system, comprising: The multi-machine grid-connected system closed-loop model establishment module is used to establish a closed-loop model of a multi-machine grid-connected system with multiple phase-locked loop converters connected to the power system; the multi-machine grid-connected system closed-loop model includes an external small-signal model and an internal small-signal model.

[0049] The homogeneous multi-machine grid-connected system construction module is used to construct the homogeneous multi-machine grid-connected system closed-loop model of the multi-machine grid-connected system.

[0050] The decoupling module is used to decouple the homogeneous multi-machine grid-connected system into multiple single-converter grid-connected subsystems.

[0051] The stability margin calculation module is used to calculate the stability margin of each single-converter grid-connected subsystem based on the generalized short-circuit ratio, and to determine the stability margin of the multi-machine grid-connected system.

[0052] This application decomposes a homogeneous multi-machine grid-connected system into multiple independent single-converter grid-connected subsystems for analysis. The calculated stability margin can accurately represent the distance from the stability limit, and combined with the short-circuit ratio of multiple substations, it also takes into account the efficiency of the calculation.

[0053] In an exemplary embodiment, a computer device is provided, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments. The computer device can be a server or a terminal. The computer device includes a processor, memory, an input / output interface (I / O), and a communication interface. The processor, memory, and I / O interface are connected via a system bus, and the communication interface is connected to the system bus via the I / O interface. The processor of the computer device provides computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and computer program in the non-volatile storage medium. The database of the computer device stores data to be processed. The I / O interface of the computer device is used for exchanging information between the processor and external devices. The communication interface of the computer device is used for communicating with an external terminal via a network connection. When the computer program is executed by the processor, it implements the above-described methods.

[0054] In one exemplary embodiment, a computer device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments.

[0055] In one exemplary embodiment, a computer-readable storage medium is provided storing a computer program that, when executed by a processor, implements the steps in the above-described method embodiments.

[0056] In one exemplary embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above-described method embodiments.

[0057] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.

[0058] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by hardware related to computer program instructions. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM).

[0059] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0060] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for calculating the stability margin of a multi-machine grid-connected system, characterized in that, include: A closed-loop model of a multi-machine grid-connected system with multiple phase-locked loop converters connected to the power system is established; the closed-loop model of the multi-machine grid-connected system includes an external small-signal model and an internal small-signal model. Construct a closed-loop model of the aforementioned multi-machine grid-connected system; The homogeneous multi-machine grid-connected system is decoupled into multiple single-converter grid-connected subsystems; Based on the generalized short-circuit ratio, the stability margin of each single-converter grid-connected subsystem is calculated, and the stability margin of the multi-machine grid-connected system is determined.

2. The method for calculating the stability margin of a multi-machine grid-connected system according to claim 1, characterized in that, Establish a closed-loop model for a multi-machine grid-connected system with multiple phase-locked loop converters connected to the power system, specifically including: For any line connected to an adjacent passive node in a new energy power system with multiple converters connected to the grid, the dynamic equation is determined according to the impedance method. With the current injection disturbance of the passive node being zero, the admittance matrix of the node after compression is determined by eliminating the internal nodes according to the Kronal mass reduction method. The dynamic behavior of the converter injecting into the AC grid is determined based on the admittance matrix and the dynamic equation; the dynamic behavior of the converter injecting into the AC grid is an external small-signal model. Based on the relationship between the local coordinate system and the global rotating coordinate system of each converter in a multi-machine grid-connected system, determine the dynamic equation of any converter in the global rotating coordinate system. Based on the dynamic equations of any converter in the global rotating coordinate system, the internal small-signal model of the entire multi-machine grid-connected system is extended.

3. The method for calculating the stability margin of a multi-machine grid-connected system according to claim 2, characterized in that, The external small-signal model is: in, = , The amount of current injected into the AC grid for n converters. Let i be the direct-axis current value injected into the AC grid for the i-th converter. The quadrature-axis current value injected into the AC grid for the i-th converter, i=1,2,3...,n; = , This is the voltage vector of the converter. Let i be the direct-axis voltage value of the i-th converter. Let i be the quadrature-axis voltage value of the i-th converter; The admittance matrix after node compression; F ( s () represents the dynamic characteristics of the converter.

4. The method for calculating the stability margin of a multi-machine grid-connected system according to claim 3, characterized in that, The internal small-signal model is as follows: in, It is a diagonal block matrix composed of the converter admittance matrix; The capacity coefficient of the i-th converter; Here is the complex frequency domain expression for the admittance of the i-th converter; Let be the complex frequency domain d-axis expression for the admittance of the i-th converter; Let be the complex frequency domain q-axis expression for the admittance of the i-th converter.

5. The method for calculating the stability margin of a multi-machine grid-connected system according to claim 1, characterized in that, The homogeneous multi-machine grid-connected system is decoupled into multiple single-converter grid-connected subsystems, specifically including: use The homogeneous multi-machine grid-connected system is decoupled into multiple single-converter grid-connected subsystems; wherein... It is the identity matrix; It is a weighted Laplace matrix composed of the capacity ratio matrix and the network admittance matrix, and this weighted Laplace matrix is ​​a positive definite matrix; W is the short-circuit ratio; W is an invertible matrix. It is a 2D identity matrix; This is the converter admittance matrix; For diagonalization formula, , For matrix n eigenvalues.

6. The method for calculating the stability margin of a multi-machine grid-connected system according to claim 1, characterized in that, Stability margin of the i-th single-converter grid-connected subsystem for: in, This is the open-loop transfer function for a single-converter grid-connected subsystem.

7. A stability margin calculation system for a multi-machine grid-connected system, characterized in that, include: The multi-machine grid-connected system closed-loop model establishment module is used to establish a closed-loop model of a multi-machine grid-connected system with multiple phase-locked loop converters connected to the power system; the multi-machine grid-connected system closed-loop model includes an external small-signal model and an internal small-signal model. A homogeneous multi-machine grid-connected system construction module is used to construct the homogeneous multi-machine grid-connected system of the closed-loop model of the multi-machine grid-connected system. The decoupling module is used to decouple the homogeneous multi-machine grid-connected system into multiple single-converter grid-connected subsystems; The stability margin calculation module is used to calculate the stability margin of each single-converter grid-connected subsystem based on the generalized short-circuit ratio, and to determine the stability margin of the multi-machine grid-connected system.

8. A computer device, comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the processor executes the computer program to implement the stability margin calculation method for a multi-machine grid-connected system according to any one of claims 1-6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the stability margin calculation method for a multi-machine grid-connected system as described in any one of claims 1-6.

10. A computer program product, comprising a computer program, characterized in that, When executed by a processor, the computer program implements the stability margin calculation method for a multi-machine grid-connected system as described in any one of claims 1-6.

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