A method and device for identifying instability sources in a multi-grid-connected inverter system

Abstract

The present invention discloses a method and device for identifying an instability source for a multi-grid-connected inverter system. The method comprises: obtaining first information of the system; the first information comprises line impedance parameters, a grid topology, and a topology and control parameters of each inverter; constructing a full system model of the system according to the first information; obtaining a current mode matrix according to the full system model; performing eigenvalue decomposition on the current mode matrix to obtain a current mode gain matrix; obtaining a current mode with a maximum amplitude in the current mode gain matrix to obtain a key current mode; performing participation factor analysis on the key current mode to obtain an inverter with the largest participation factor, i.e., obtaining the instability source inverter.

Description

Technical Field

[0001] The present invention relates to the field of multi-machine grid-connected inverters, and in particular to a method and device for identifying instability sources of a multi-grid-connected inverter system. Background Art

[0002] With the rapid adoption of renewable energy, multi-grid-connected inverter systems have become a critical component of modern power grids. As key power electronics, grid-connected inverters are the foundation for the integration of photovoltaic arrays, wind turbines, and microgrids. These systems, characterized by the parallel or networked operation of multiple inverters, offer greater flexibility and efficiency but also present complex stability challenges. Interactions between inverters, combined with grid impedance and diverse control strategies, can lead to instabilities such as harmonic oscillations, resonances, and low-frequency disturbances, threatening power quality and system reliability.

[0003] When a multi-inverter system experiences instability, identifying the source of instability and improving the system's grid-connected stability remains an unresolved issue. Traditional stability analysis techniques, such as impedance-based methods and eigenvalue analysis, often struggle to accurately identify the specific inverter or component causing instability in large systems. This complexity stems from the distributed nature of the control loop, nonlinear dynamics, and constantly changing operating conditions. Impedance-based methods leverage the frequency-domain characteristics of the inverter and the grid to assess stability. For example, the Nyquist criterion applied to the impedance ratio provides a modular approach capable of modeling the interaction between a single inverter and the grid. However, its accuracy relies heavily on accurate impedance measurement, and obtaining accurate impedance data in real time is challenging in complex systems with time-varying parameters. Furthermore, impedance-based methods can struggle to distinguish multiple potential instability sources in tightly connected systems, limiting diagnostic capabilities. Eigenvalue analysis based on the state-space matrix is ​​a traditional method that assesses system stability by analyzing the eigenvalues ​​of a linearized system model. While effective in small-scale systems, this approach becomes computationally intensive and impractical for large multi-inverter networks due to the high dimensionality of the state-space matrix. Furthermore, eigenvalue analysis often fails to provide clear insights into the specific sources of instability because it focuses on the behavior of the system as a whole rather than local effects.

[0004] Therefore, a new technical solution is proposed to solve the technical problem of how to locate the unstable source inverter in an unstable multi-grid-connected inverter system. Summary of the Invention

[0005] The present invention provides an instability source identification method and device for a multi-grid-connected inverter system, which are used to solve the technical problem of how to locate the instability source inverter in the instability multi-grid-connected inverter system.

[0006] To achieve the above objectives, the present invention provides a method for identifying instability sources for a multi-grid-connected inverter system, wherein the system includes a preset number of current-controlled inverters with the same structure, and the method includes:

[0007] Acquire first information of the system; the first information includes line impedance parameters, grid topology, and topology and control parameters of each inverter; construct a full system model of the system based on the first information; and obtain a current modal matrix based on the full system model;

[0008] The current modal gain matrix is ​​obtained by performing eigenvalue decomposition on the current modal matrix; the current mode with the largest amplitude in the current modal gain matrix is ​​obtained to obtain the key current mode; and the inverter with the largest participation factor is obtained by performing participation factor analysis on the key current mode, that is, the instability source inverter.

[0009] Preferably, constructing a full system model of the system according to the first information includes:

[0010] A current transfer model of the multi-grid-connected inverter system is constructed according to the first information; the current transfer model is transformed by considering the influence of the current control link inside the inverter to obtain a full system model.

[0011] Preferably, a current transfer model of the system is constructed based on the first information; the current transfer model is transformed by considering the influence of the current control link inside the inverter to obtain a full system model including:

[0012] The voltage-current relationship matrix of each node in the power grid is constructed according to the line impedance parameters and the power grid topology, and the first matrix is ​​obtained:

[0013] ;

[0014] in, I represents the current matrix of each node in the power grid, I 1 to I n Indicates the current of each node in the power grid; Y 11 to Y nn represents the line admittance of the power grid structure; V 1 to V n Indicates the voltage of each node in the power grid;

[0015] Extract the inverter node elements according to the first matrix, construct the current-voltage relationship matrix about the inverter output port, and obtain the second matrix:

[0016] ;

[0017] According to the second matrix combined with the circuit current-voltage relationship of the inverter Norton equivalent model, the output current model of the multi-grid-connected inverter system is obtained:

[0018] ;

[0019] ;

[0020] According to the output current model, the current transfer model of the multi-grid-connected inverter system is obtained:

[0021] ;

[0022] The current transfer model is converted according to the topology and control parameters of each inverter to obtain the full system model:

[0023] ;

[0024] in, represents the output admittance diagonal matrix of the inverter group, where the diagonal elements are the output admittance matrices of the 1st to nth grid-connected inverters; The impedance matrix representing the inverter node current-voltage relationship; Represents the admittance matrix of current and voltage relationships at each node in the power grid architecture; represents the unit diagonal matrix; represents the current transfer matrix; represents the inverter equivalent current source matrix; represents the inverter output port current matrix; represents the inverter internal control current transfer matrix, represents the inverter current reference value matrix; to Indicates the voltage of each inverter access node; to Indicates the output current of each inverter.

[0025] Preferably, the current mode matrix includes:

[0026] ;

[0027] ;

[0028] ;

[0029] in, Represents the current mode matrix, which includes grid architecture information, internal control parameters of each inverter, and output impedance information of each inverter.

[0030] Preferably, performing eigenvalue decomposition on the current mode matrix to obtain a current mode gain matrix; obtaining the current mode with the maximum amplitude in the current mode gain matrix, and obtaining the key current mode includes:

[0031] Perform eigenvalue decomposition on the current mode matrix to obtain the current mode gain matrix:

[0032] ;

[0033] ;

[0034] in, represents the eigenvector matrix; represents the inverse eigenvector matrix; represents the current mode gain matrix; to represents the current mode gain;

[0035] Get the current mode with the largest amplitude in the current mode gain matrix, that is, from the current mode gain to The current mode with the maximum amplitude is obtained from the equation , and the key current mode is obtained.

[0036] Preferably, performing participation factor analysis based on key current modes to obtain an inverter with the largest participation factor, that is, obtaining an instability source inverter, includes:

[0037] The system frequency point where the maximum amplitude appears in the key current mode Conducting factor analysis:

[0038] Through the system frequency point at Matrix and The inner product of the eigenvectors corresponding to the key current modes in the matrix is ​​performed to obtain the participation factor of each inverter with respect to the maximum amplitude of the key current mode. The inverter with the largest participation factor is the instability source inverter.

[0039] The present invention also provides an instability source identification device for a multi-grid-connected inverter system, which is used in the method of the present invention. The device includes a first module, a second module, a third module and a fourth module;

[0040] The first module is used to obtain first information of the system; the first information includes line impedance parameters, grid topology, and topology and control parameters of each inverter;

[0041] The second module is used to construct a full system model of the system based on the first information;

[0042] The third module is used to obtain the current mode matrix according to the full system model; perform eigenvalue decomposition on the current mode matrix to obtain the current mode gain matrix;

[0043] The fourth module is used to obtain the current mode with the largest amplitude in the current mode gain matrix to obtain the key current mode; based on the key current mode, a participation factor analysis is performed to obtain the inverter with the largest participation factor, that is, the instability source inverter.

[0044] The present invention also provides a computer medium, characterized in that it includes a processor, a memory, and a computer program for implementing the method of the present invention.

[0045] The present invention has the following beneficial effects:

[0046] The instability source identification method for a multi-grid-connected inverter system of the present invention constructs a full-system model of the multi-grid-connected inverter system based on line impedance parameters, grid voltage parameters, grid topology, the topology of each inverter, and the control parameters of each inverter. Compared with traditional modeling methods, the full-system model is more comprehensive and the modeling is more refined, making the subsequent calculations of the method more accurate. When harmonic oscillation occurs in the multi-grid-connected inverter system, the current mode matrix is ​​obtained according to the full-system model of the present invention, and the subsequent calculation of the system instability source is performed based on the current mode matrix, which can provide guidance for further improving the stability of the system. The method of the present invention can be compiled by a computer and is fast, efficient, and easy to operate.

[0047] The instability source identification device for a multi-grid-connected inverter system of the present invention is used in the method of the present invention and has the same beneficial effects as the method of the present invention.

[0048] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0050] Figure 1 It is a schematic diagram of a method flow of a preferred embodiment of the present invention.

[0051] Figure 2 It is a structural diagram of a current closed-loop controlled grid-following inverter according to a preferred embodiment of the present invention.

[0052] Figure 3 It is a structural diagram of a three-current closed-loop control type grid-following inverter interconnection system according to a preferred embodiment of the present invention.

[0053] Figure 4 1 is a schematic diagram of the results of current modal gain analysis performed based on the full system model of the present invention in a preferred embodiment of the present invention.

[0054] Figure 5 2 is a schematic diagram of the analysis results of the key current mode gain participation factor of the preferred embodiment of the present invention.

[0055] Figure 6 1 is an experimental waveform diagram of the output current of the inverter 1 when harmonic oscillation occurs in the system of the preferred embodiment of the present invention.

[0056] Figure 7 1 is an experimental waveform diagram of the output current of the inverter 2 when harmonic oscillation occurs in the system of the preferred embodiment of the present invention.

[0057] Figure 8 1 is an experimental waveform diagram of the output current of the inverter 3 when harmonic oscillation occurs in the system of the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0058] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0059] See also Figure 1 In a preferred embodiment of the present invention, a method for identifying an instability source for a multi-grid-connected inverter system is provided. The system includes a preset number of current-controlled inverters with the same structure. The method includes:

[0060] S1. Acquire first information of the system; the first information includes line impedance parameters, grid topology, and topology and control parameters of each inverter.

[0061] S2. Construct a full system model of the system according to the first information; and obtain a current modal matrix according to the full system model.

[0062] In a preferred embodiment of the present invention, constructing a full system model of the system based on the first information includes:

[0063] A current transfer model of a multi-grid-connected inverter system is constructed based on the first information; the current transfer model is transformed by considering the influence of the current control link inside the inverter to obtain a full system model. Specifically, the following steps are included:

[0064] The voltage-current relationship matrix of each node in the power grid is constructed according to the line impedance parameters and the power grid topology, and the first matrix is ​​obtained:

[0065] ;

[0066] in, Irepresents the current matrix of each node in the power grid, I 1 to I n Indicates the current of each node in the power grid; Y 11 to Y nn represents the line admittance of the power grid structure; V 1 to V n Indicates the voltage of each node in the power grid;

[0067] Extract the inverter node elements according to the first matrix, construct the current-voltage relationship matrix about the inverter output port, and obtain the second matrix:

[0068] ;

[0069] According to the second matrix combined with the circuit current-voltage relationship of the inverter Norton equivalent model, the output current model of the multi-grid-connected inverter system is obtained:

[0070] ;

[0071] ;

[0072] According to the output current model, the current transfer model of the multi-grid-connected inverter system is obtained:

[0073] ;

[0074] The current transfer model is converted according to the topology and control parameters of each inverter to obtain the full system model:

[0075] ;

[0076] in, represents the output admittance diagonal matrix of the inverter group, where the diagonal elements are the output admittance matrices of the 1st to nth grid-connected inverters; The impedance matrix representing the inverter node current-voltage relationship; Represents the admittance matrix of current and voltage relationships at each node in the power grid architecture; represents the unit diagonal matrix; represents the current transfer matrix; represents the inverter equivalent current source matrix; represents the inverter output port current matrix; represents the inverter internal control current transfer matrix, represents the inverter current reference value matrix; to Indicates the voltage of each inverter access node; to Indicates the output current of each inverter.

[0077] In a preferred embodiment of the present invention, the current mode matrix includes:

[0078] ;

[0079] ;

[0080] ;

[0081] in, Represents the current mode matrix, which includes grid architecture information, internal control parameters of each inverter, and output impedance information of each inverter.

[0082] S3. Perform eigenvalue decomposition on the current modal matrix to obtain a current modal gain matrix; obtain the current mode with the maximum amplitude in the current modal gain matrix to obtain the key current mode. S3 specifically includes:

[0083] Perform eigenvalue decomposition on the current mode matrix to obtain the current mode gain matrix:

[0084] ;

[0085] ;

[0086] in, represents the eigenvector matrix; represents the inverse eigenvector matrix; represents the current mode gain matrix; to represents the current mode gain;

[0087] Get the current mode with the largest amplitude in the current mode gain matrix, that is, from the current mode gain to The current mode with the maximum amplitude is obtained from the equation , and the key current mode is obtained.

[0088] S4. Perform participation factor analysis based on the key current modes to obtain the inverter with the largest participation factor, that is, the instability source inverter. S4 specifically includes:

[0089] The system frequency point where the maximum amplitude appears in the key current mode Conducting factor analysis:

[0090] Through the system frequency point at Matrix and The inner product of the eigenvectors corresponding to the key current modes in the matrix is ​​performed to obtain the participation factor of each inverter with respect to the maximum amplitude of the key current mode. The inverter with the largest participation factor is the instability source inverter.

[0091] The instability source identification method for a multi-grid-connected inverter system of the present invention constructs a full-system model of the multi-grid-connected inverter system based on line impedance parameters, grid voltage parameters, grid topology, the topology of each inverter, and the control parameters of each inverter. Compared with traditional modeling methods, the full-system model is more comprehensive and the modeling is more refined, making the subsequent calculations of the method more accurate. When harmonic oscillation occurs in the multi-grid-connected inverter system, the current mode matrix is ​​obtained according to the full-system model of the present invention, and the subsequent calculation of the system instability source is performed based on the current mode matrix, which can provide guidance for further improving the stability of the system. The method of the present invention can be compiled by a computer and is fast, efficient, and easy to operate.

[0092] In a preferred embodiment of the present invention, there is also provided an instability source identification device for a multi-grid-connected inverter system, which is used in the method of the present invention, and the device includes a first module, a second module, a third module and a fourth module;

[0093] The first module is used to obtain first information of the system; the first information includes line impedance parameters, grid topology, and topology and control parameters of each inverter;

[0094] The second module is used to construct a full system model of the system based on the first information;

[0095] The third module is used to obtain the current mode matrix according to the full system model; perform eigenvalue decomposition on the current mode matrix to obtain the current mode gain matrix;

[0096] The fourth module is used to obtain the current mode with the largest amplitude in the current mode gain matrix to obtain the key current mode; based on the key current mode, a participation factor analysis is performed to obtain the inverter with the largest participation factor, that is, the instability source inverter.

[0097] The instability source identification device for a multi-grid-connected inverter system of the present invention is used in the method of the present invention and has the same beneficial effects as the method of the present invention.

[0098] In a preferred embodiment of the present invention, a computer medium is further provided, comprising a processor, a memory, and a computer program for implementing the method of the present invention.

[0099] Verification part:

[0100] In a preferred embodiment of the present invention, a set of three current closed-loop control type grid-following inverter interconnection systems is built in MATLAB / Simulink. The simulation parameters are shown in Table 1:

[0101] Table 1 Simulation parameters

[0102] ;

[0103] The structure of the current closed-loop control type grid-following inverter is shown in Figure 2 .exist Figure 2 middle, is the DC side voltage, is the modulation gain, is the inverter side filter inductor, is the grid-side filter inductor, is the filter damping resistance, is the filter capacitance, is the grid connection point voltage, For the phase-locked loop, for The obtained phase angle, is the inverter output current, is the grid-side output current, is the inverter dq axis reference value, is the inverter current controller, Modulate the voltage signal for the inverter, is the grid impedance, is the grid voltage, is the inverter output port voltage, are the d-axis and q-axis currents output by the grid side; abc / dq represents dq transformation; and dq / abc represents inverse dq transformation.

[0104] The structure of the interconnected system of three current closed-loop controlled grid-following inverters is shown in Figure 3 At this time, the number of inverters in parallel n is 3, and the grid structure adopts a three-parallel structure. Inverter 1, inverter 2, and inverter 3 are connected in parallel at nodes 3, 13, and 14 respectively.

[0105] Assume that the system has harmonic oscillation when the grid impedance is 2.8mH. To verify the effectiveness of the method of the present invention, the current modal gain analysis is performed based on the full system model of the present invention. The analysis results are shown in Figure 4 λ1 to λ6 are the current modal gains. The results show that the current modal gain λ1 has a maximum amplitude point, so the current modal gain λ1 is the key current modal gain of the system. The frequency corresponding to the maximum amplitude point is x Hz, which lays the foundation for the subsequent calculation of the participation factors of each inverter.

[0106] The analysis results of the key current mode gain participation factors of each inverter based on the full system model are shown in Figure 5The results show that inverter 1 is the main participant in the harmonic oscillation of the system, and its participation factor reaches a maximum of 0.3745; inverter 2 and inverter 3 are secondary participants in the harmonic oscillation of the system, and their participation factors reach a maximum of 0.1052 and 0.1030 respectively.

[0107] Figures 6 to 8 The experimental waveforms of the output currents of inverter 1, inverter 2, and inverter 3 are shown when the grid impedance is 2.8mH and the multi-inverter system generates harmonic oscillation. i 2a 、 i 2b and i 2c The results show that when harmonic oscillation occurs in the system, the current waveforms of Inverter 2 and Inverter 3 can still maintain a certain stable output. However, the current waveform of Inverter 1 exhibits obvious harmonic oscillation and loses stability. This means that Inverter 1 is the primary contributor to the harmonic oscillation instability in the system. This is consistent with the theoretical analysis above and verifies the effectiveness and correctness of the present invention.

[0108] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for identifying instability sources in a multi-grid-connected inverter system, characterized in that: The system includes a preset number of current-controlled inverters with identical structures, and the method includes: Acquiring first information of the system; the first information including line impedance parameters, grid topology, and topology and control parameters of each inverter; constructing a full system model of the system based on the first information; and obtaining a current modal matrix based on the full system model; Performing eigenvalue decomposition on the current modal matrix to obtain a current modal gain matrix; obtaining the current mode with the largest amplitude in the current modal gain matrix to obtain a key current mode; performing participation factor analysis on the key current mode to obtain an inverter with the largest participation factor, that is, obtaining an instability source inverter; The constructing of the full system model of the system according to the first information includes: Constructing a current transfer model of the multi-grid-connected inverter system based on the first information; transforming the current transfer model by considering the influence of the current control link inside the inverter to obtain a full system model, specifically including: A voltage-current relationship matrix of each node in the power grid is constructed according to the line impedance parameters and the power grid topology to obtain a first matrix: ； in, I represents the current matrix of each node in the power grid, I 1 to I n Indicates the current of each node in the power grid; Y 11 to Y nn represents the line admittance of the power grid structure; V 1 to V n Indicates the voltage of each node in the power grid; The inverter node elements are extracted according to the first matrix, and the current-voltage relationship matrix of the inverter output port is constructed to obtain the second matrix: ； The output current model of the multi-grid-connected inverter system is obtained according to the second matrix combined with the circuit current-voltage relationship of the inverter Norton equivalent model: ； ； The current transfer model of the multi-grid-connected inverter system is obtained according to the output current model: ； The current transfer model is converted according to the topology and control parameters of each inverter to obtain a full system model: ； in, represents the output admittance diagonal matrix of the inverter group, where the diagonal elements are the output admittance matrices of the 1st to nth grid-connected inverters; The impedance matrix representing the inverter node current-voltage relationship; Represents the admittance matrix of current and voltage relationships at each node in the power grid architecture; represents the unit diagonal matrix; represents the current transfer matrix; represents the inverter equivalent current source matrix; represents the inverter output port current matrix; represents the inverter internal control current transfer matrix, represents the inverter current reference value matrix; to Indicates the voltage of each inverter access node; to Indicates the output current of each inverter.

2. The instability source identification method for a multi-grid-connected inverter system according to claim 1, characterized in that: The current mode matrix includes: ； ； ； in, Represents the current mode matrix, which includes grid architecture information, internal control parameters of each inverter, and output impedance information of each inverter.

3. The instability source identification method for a multi-grid-connected inverter system according to claim 2, characterized in that: Performing eigenvalue decomposition on the current mode matrix to obtain a current mode gain matrix; Obtaining the current mode with the maximum amplitude in the current mode gain matrix, and obtaining the key current mode includes: Perform eigenvalue decomposition on the current mode matrix to obtain the current mode gain matrix: ； ； in, represents the eigenvector matrix; represents the inverse eigenvector matrix; represents the current mode gain matrix; to represents the current mode gain; Obtain the current mode with the maximum amplitude in the current mode gain matrix, that is, from the current mode gain to The current mode with the maximum amplitude is obtained to obtain the key current mode.

4. The instability source identification method for a multi-grid-connected inverter system according to claim 3, characterized in that: The inverter with the largest participation factor is obtained by performing participation factor analysis based on the key current mode, that is, the inverter with the largest participation factor is obtained, which includes: The system frequency point where the maximum amplitude appears in the key current mode Conduct participation factor analysis: Through the system frequency point at Matrix and The inner product of the eigenvectors corresponding to the key current modes in the matrix is ​​performed to obtain the participation factor of each inverter with respect to the maximum amplitude of the key current mode, wherein the inverter with the largest participation factor is the instability source inverter.

5. An instability source identification device for a multi-grid-connected inverter system, used in the method according to any one of claims 1 to 4, characterized in that: The device includes a first module, a second module, a third module and a fourth module; The first module is used to obtain first information of the system; the first information includes line impedance parameters, grid topology, and topology and control parameters of each inverter; The second module is used to construct a full system model of the system according to the first information; The third module is used to obtain a current mode matrix according to the full system model; perform eigenvalue decomposition on the current mode matrix to obtain a current mode gain matrix; The fourth module is used to obtain the current mode with the largest amplitude in the current mode gain matrix to obtain the key current mode; perform participation factor analysis based on the key current mode to obtain the inverter with the largest participation factor, that is, to obtain the instability source inverter.

6. A computer medium, characterized in that The method comprises a processor, a memory and a computer program for implementing the method according to any one of claims 1 to 4.

Images