Multi-machine grid-connected inverter impedance modeling method and related equipment

Abstract

The invention discloses a multi-machine grid-connected inverter impedance modeling method and related equipment, and belongs to the field of renewable energy power generation, and the method comprises the following steps: carrying out grid-connected inverter impedance modeling based on a frequency coupling effect, and obtaining a final admittance matrix; and establishing an impedance model for each inverter in the current collection line according to the final admittance matrix, establishing an equivalent current collection line model according to the impedance model, calculating the equivalent high-frequency impedance of each link in the equivalent current collection line model, and obtaining a multi-machine grid-connected inverter impedance model according to the equivalent high-frequency impedance of each link. According to the method, the problem of inaccurate stability analysis caused by inaccurate modeling in the prior art can be solved.

Description

Technical Field

[0001] The invention belongs to the field of renewable energy power generation, and in particular relates to an impedance modeling method for a multi-machine grid-connected inverter and related equipment. Background Art

[0002] With the continuous development of wind power, photovoltaic power generation and high-voltage AC and DC transmission technology, the weakly synchronous power grid system dominated by high-proportion power electronic devices such as wind turbines, photovoltaic stations, high-voltage DC, and reactive power compensation is the main feature of my country's new energy grid-connected system. The complex control effects of a large number of devices are intertwined with the characteristics of weakly synchronous power grids, making the dynamic characteristics of new energy grid-connected systems extremely complex and the stability issues prominent. The impedance analysis method has the advantages of clear physical meaning, intuitiveness and measurability, and is currently widely used in the stability analysis of new energy grid-connected systems. However, most of the current stability analysis content models for system models are relatively simple, often ignoring the frequency coupling effect caused by the DC side voltage control loop of the inverter and the influence of the collector line on the model, which may lead to inaccurate modeling and inability to accurately perform stability analysis. Summary of the invention

[0003] The purpose of the present invention is to provide a multi-machine grid-connected inverter impedance modeling method and related equipment, which can take into account the frequency coupling effect caused by the inverter DC side voltage control loop and the multi-machine grid-connected collection line model during stability analysis, so as to solve the problem of inaccurate modeling in the prior art, thereby causing inaccurate stability analysis.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, a method for impedance modeling of a multi-machine grid-connected inverter comprises the following steps: Based on the frequency coupling effect, the grid-connected inverter impedance modeling is carried out to obtain the final admittance matrix; An impedance model is established for each inverter in the collector line according to the final admittance matrix, an equivalent collector line model is established according to the impedance model, the equivalent high-frequency impedance of each link in the equivalent collector line model is calculated, and the impedance model of the multi-machine grid-connected inverter is obtained according to the equivalent high-frequency impedance of each link.

[0005] In some implementations, the step of performing grid-connected inverter impedance modeling based on the frequency coupling effect specifically includes: Obtaining the port characteristic expression of the grid-connected inverter based on the frequency coupling relationship; The DC voltage loop, phase-locked loop, current loop and modulation process of the grid-connected inverter are modeled, and the influence of the frequency coupling effect on the grid-connected inverter is analyzed; The final admittance matrix is ​​obtained by combining the port characteristic expression and the influence relationship.

[0006] In some implementations, the port characteristic expression is as follows (7): (7) in, is the disturbance frequency, In response to the current, is the coupling current, is the disturbance voltage, is the fundamental frequency, is the influence coefficient of positive sequence voltage on positive sequence current response, is the influence coefficient of positive sequence voltage on negative sequence current response, is the influence coefficient of negative sequence voltage on positive sequence current response, is the influence coefficient of negative sequence voltage on negative sequence current response.

[0007] In some embodiments, the influence relationship of the frequency coupling effect on the grid-connected inverter includes: the influence relationship of the disturbance voltage and the response current on the DC bus voltage, the influence relationship of the DC bus voltage and the inverter output voltage, the influence relationship of the disturbance voltage and the response current, and the influence relationship of the disturbance voltage and the inverter port voltage; The influence relationship between the disturbance voltage and the response current on the DC bus voltage is expressed as follows (18): (18) in, It is the equivalent DC current source of the new energy power generation device. represents the DC side capacitance, is the DC side voltage control reference value, is the conjugate of the fundamental frequency current, is the fundamental frequency current, , is the disturbance frequency, is the grid voltage fundamental frequency amplitude, is the filter inductor, and They are the influence matrix coefficients of different corresponding response currents on DC voltage, and They are the influence matrix coefficients of different disturbance voltages on DC voltage; The influence relationship between the DC bus voltage and the inverter output voltage is as follows (19): (19) in, is the fundamental frequency component of the modulated signal, is the conjugate of the fundamental frequency component of the modulating signal, is the transfer function of the DC voltage loop controller, is the transfer function of the d-axis control parameters, and They represent the influence coefficients of different DC bus voltages on the inverter output voltage. is the modulation coefficient; The influence relationship between the disturbance voltage and the response current is as follows (20): (20) in, is the current loop d-axis regulator transfer function, is the current loop q-axis regulator transfer function, , , and They represent the influence matrix coefficients of different disturbance voltages on the response current, is the modulation coefficient, is the decoupling coefficient; The influence relationship between the disturbance voltage and the inverter port voltage is as follows (21): (twenty one)

[0008] in, , , and They represent the influence matrix coefficients of different disturbance voltages on the inverter port voltage. is the phase-locked loop transfer function.

[0009] In some embodiments, the final admittance matrix is ​​the following formula (22): (twenty two) in, and They respectively represent the influence coefficients of different DC bus voltages on the inverter output voltage.

[0010] In some implementations, the equivalent high-frequency impedance of each link is expressed as follows (25): (25) in, Indicates link x The equivalent impedance of the upper inverter is For Link x The equivalent capacitance to ground between the upper units, For Link x The equivalent impedance between the upper units, Indicates link x The equivalent collector line and unit admittance, Indicates link x The capacitance of the cable line to ground, Indicates link x The impedance of the cable line, For the entire link x The total impedance of

[0011] In a second aspect, a multi-machine grid-connected inverter impedance modeling system includes: Single grid-connected inverter impedance modeling module, used to model the grid-connected inverter impedance based on frequency coupling effect and obtain the final admittance matrix; The multi-machine grid-connected inverter impedance modeling module is used to establish an impedance model for each inverter in the collector line according to the final admittance matrix, establish an equivalent collector line model according to the impedance model, calculate the equivalent high-frequency impedance of each link in the equivalent collector line model, and obtain the multi-machine grid-connected inverter impedance model according to the equivalent high-frequency impedance of each link.

[0012] In a third aspect, a computer device comprises a memory, a processor, and a computer program stored in the memory and executable in the processor, wherein the processor implements the steps of the impedance modeling method for a multi-machine grid-connected inverter when executing the computer program.

[0013] In a fourth aspect, a computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the impedance modeling method of a multi-machine grid-connected inverter are implemented.

[0014] In a fifth aspect, a computer program product is provided, comprising a computer program, wherein the computer program implements the steps of the impedance modeling method for a multi-machine grid-connected inverter when the computer program is executed by a processor.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a multi-machine grid-connected inverter impedance modeling method, which performs grid-connected inverter impedance modeling based on the frequency coupling effect to obtain a final admittance matrix; then, an impedance model is established for each inverter in the collector line according to the final admittance matrix, an equivalent collector line model is established according to the impedance model, and the equivalent high-frequency impedance of each link in the equivalent collector line model is calculated, and the multi-machine grid-connected inverter impedance model is obtained according to the equivalent high-frequency impedance of each link. Based on the modeling using the harmonic linearization method, the present invention can accurately model the inverter impedance considering the voltage and current closed loop, and the overall model considers the line model of the multi-machine grid connection, which is more conducive to accurate stability analysis. The present invention establishes a grid-connected inverter impedance model considering the frequency coupling effect, expands the impedance into two dimensions, and is more accurate when analyzing the stability of the low-frequency band.

[0016] Furthermore, the present invention obtains the port characteristic expression of the grid-connected inverter based on the frequency coupling relationship; models the DC voltage loop, phase-locked loop, current loop and modulation process of the grid-connected inverter, and analyzes the influence relationship of the frequency coupling effect on the grid-connected inverter; combines the port characteristic expression and the influence relationship to obtain the final admittance matrix. Typical control structures such as voltage and current dual closed loops, synchronous coordinate system phase-locked loops, etc., as well as typical multi-machine model topology structures are selected to make the established multi-machine grid-connected inverter impedance model more universal. And the established multi-machine grid-connected inverter impedance model performs equivalent modeling of the inter-unit collector line in the multi-machine modeling on the single grid-connected inverter impedance model, so that the model can take into account the accuracy of high-frequency stability analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a topological diagram of a three-phase grid-connected inverter in an embodiment of the present invention; Figure 2 is a frequency coupling characteristic relationship diagram of a three-phase grid-connected inverter in an embodiment of the present invention; Figure 3 is a schematic diagram of an equivalent model of a current collection circuit in an embodiment of the present invention; Figure 4 A schematic diagram of the overall framework of a multi-machine grid-connected inverter impedance modeling method provided by an embodiment of the present invention; Figure 5 A schematic flow chart of a method for modeling impedance of a multi-machine grid-connected inverter provided by an embodiment of the present invention; Figure 6 A structural diagram of a multi-machine grid-connected inverter impedance modeling system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings, and the described content is intended to explain the present invention rather than to limit it.

[0019] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or are inherent to these processes, methods, systems, products or apparatus.

[0020] like Figure 4 and Figure 5As shown, this embodiment provides a multi-machine grid-connected inverter impedance modeling method. On the basis of modeling using harmonic linearization, the inverter impedance of the voltage and current closed loop can be considered for accurate modeling, and the overall model considers the line model of the multi-machine grid-connected, which is more conducive to accurate stability analysis, including the following steps: S1, grid-connected inverter impedance modeling considering frequency coupling effect; S1.1, Analysis of the mechanism of frequency coupling effect of grid-connected inverter. Figure 1 The topology diagram of the three-phase grid-connected inverter under study is shown in Figure 2. When studying the output impedance, the frequency injected at the common grid connection point (PCC) is The three-phase symmetrical disturbance voltage is measured and the current response at the PCC is measured. The fundamental frequency is Further FFT analysis shows that the same frequency The disturbance current component and frequency are Further research and analysis can reveal the frequency coupling relationship of the grid-connected inverter, such as Figure 2 The principle can be explained as follows: the injection frequency at the PCC point is The disturbance voltage go through The frequency of generation is The response current At the same time, the frequency coupling that may be caused by asymmetric control will cause the disturbance voltage to pass through The frequency generated in PCC is The coupling current , the coupling current The voltage disturbance of the same frequency is generated through the grid impedance , voltage disturbance The coupling frequency is The coupling current forms a cycle.

[0021] Considering that the average model of the grid-connected inverter system can generally be expressed as: (1) (2) in It represents the DC current source equivalent to the new energy power generation device. represents the DC side capacitance, represents the DC bus capacitor voltage, , , Respectively represent the three-phase output port voltage of the inverter.

[0022] Assuming that the PCC disturbance voltage is the positive sequence component, taking phase a as an example, according to the frequency coupling relationship, the time domain expressions of phase a voltage and current at the grid connection point can be written as (3)(4): (3) (4) in, is the initial phase of the positive sequence disturbance voltage, is the initial phase of negative sequence disturbance voltage, is the negative sequence disturbance frequency, is the initial phase of the fundamental frequency current, is the initial phase of the positive sequence disturbance response current, It is the initial phase of the negative sequence disturbance response current.

[0023] Write (3) (4) in the frequency domain, the expressions are: (5) (6) in, , , , , , .

[0024] According to this analysis, after considering the frequency coupling characteristics, the port characteristics of the grid-connected inverter and the elements of the two-dimensional admittance matrix , , and Therefore, the port characteristic expression of the grid-connected inverter can be written as: (7) S1.2, DC voltage loop modeling of grid-connected inverter. According to the average model of grid-connected inverter established by equations (1)-(2), substituting (1) into (2) can obtain the expression (8) of the DC bus voltage disturbance component in the frequency domain.

[0025] (8) In the formula is the DC side voltage control reference value, is the fundamental frequency current The conjugate of. Furthermore, since the instantaneous power on the AC and DC sides is equal, the disturbance components of the voltage and current on the AC and DC sides will affect each other, as shown in formula (8). In the inverter control loop considered in the present invention, the input of the voltage control loop is the DC side capacitor voltage and reference value, and the output is the d-axis current reference value, so the disturbance of the DC side capacitor voltage will also cause the output response disturbance component, which can be written as: (9) in is the transfer function of the DC voltage loop controller, The disturbance frequency is The response disturbance component of the d-axis current reference value.

[0026] S1.3, modeling of phase-locked loop, current loop and modulation part. According to the phase-locked loop structure in the traditional synchronous coordinate system, considering the influence of frequency coupling on the traditional phase-locked loop transfer function, the expression of the phase angle disturbance of the phase-locked loop output is written as: (10) in , through the convolution operation, we can get The expression is: (11) Before deriving the current loop model, according to equation (11), the coordinate transformation is obtained d Axis and q The shaft current will be affected by the phase-locked loop output angle disturbance component, based on which it can be deduced d Axis and q Frequency domain expression of shaft current: (12) (13) in, is the initial phase of the fundamental frequency current.

[0027] According to the control structure of the current loop, we can get d Axis and q The disturbance component expression of the axis modulation signal. It should be noted that when considering frequency coupling, the asymmetry of the outer loop control structure is taken into account, and the imbalance of the current loop control parameters is taken into account during modeling, that is: (14) (15) in, is the current loop d-axis regulator transfer function, is the transfer function of the d-axis control parameters, is the transfer function of the q-axis control parameter.

[0028] Further considering the modulation process, taking phase a as an example, considering the time domain expression of the inverter output voltage and the modulation signal (16): (16) in, is the time domain component of the inverter a-phase output port voltage, is the time domain component of the DC bus voltage, is the time domain component of the inverter a-phase modulation signal.

[0029] The frequency domain component of the inverter a-phase output port voltage is equal to the convolution of the frequency domain component of the DC bus voltage and the frequency domain component of the a-phase modulation signal, that is: (17) in represents the fundamental frequency component of the modulated signal, .

[0030] Based on the above analysis, in order to simplify the final expression, the following groups of expressions are introduced to represent the different effects of frequency coupling.

[0031] The influence of the disturbance voltage and the response current on the DC bus voltage can be expressed as the following matrix expression according to equation (8): (18) The relationship between the DC bus voltage and the inverter output voltage can be written as: (19) The relationship between the disturbance voltage and the response current (influenced by the current controller) can be written as: (20) The influence relationship between the disturbance voltage and the inverter port voltage (influenced by the phase-locked loop) can be written as: (twenty one) After three steps of integration, the final form of the admittance matrix is: (twenty two) S2, considering the collector line model to model the impedance of multi-machine grid-connected inverter; S2.1, according to the grid-connected inverter impedance model considering the frequency coupling effect obtained in S1, when considering the multi-machine modeling line, each individual inverter is regarded as the model of formula (22). Since the line model involves high-frequency stability analysis, it is possible to consider simplifying the impedance model of the inverter.

[0032] When establishing the line model, the collector line model is first considered. For the collector lines between the units on each link, the present invention intends to use the equal power loss method for equivalence, that is, the loss of the collector line before and after the equivalence is unchanged as a principle. Figure 3 The collector circuit shown is used as an example for equivalence, and the calculation formula is as follows: (twenty three) After equivalence, we have: (twenty four) In particular, if there is capacitance on the collector circuit, the equivalent capacitance can be regarded as the sum of the capacitances of the collector circuits before the equivalent capacitance, ignoring the voltage difference.

[0033] Comprehensive analysis, for link x For , the equivalent high-frequency impedance of the link can be obtained after equalization: (25) In formula (25), Indicates link x The equivalent impedance of the upper inverter is For Link x The equivalent capacitance to ground between the upper units, For Link x The equivalent impedance between the upper units, Indicates link x The equivalent collector line and unit admittance, Indicates link x The capacitance of the cable line to ground, Indicates link x The impedance of the cable line can be seen that equation (25) is calculated twice because the collector line between the units is considered. The circuit is equivalent to the whole link. x The total impedance Finally, the equivalent impedance model of the overall system can be obtained by calculating each link. After considering the high-frequency impedance characteristics of the line, the impedance model has higher accuracy in the high-frequency band and has full-frequency accuracy.

[0034] This embodiment provides a multi-machine grid-connected inverter impedance modeling method. By establishing a grid-connected inverter impedance model that considers the frequency coupling effect, the impedance is expanded to two dimensions, which is more accurate when analyzing the stability in the low-frequency band; typical control structures (voltage and current double closed loops, synchronous coordinate system phase-locked loops, etc.) and typical multi-machine model topology structures are selected to make the conclusions more universal. The equivalent modeling of the inter-unit collector line in the multi-machine modeling is discussed on the basis of the conventional model, so that the model can take into account the accuracy of the high-frequency stability analysis, making the conclusions more practical.

[0035] like Figure 6 As shown, this embodiment also provides a multi-machine grid-connected inverter impedance modeling system, including: Single grid-connected inverter impedance modeling module, used to model the grid-connected inverter impedance based on frequency coupling effect and obtain the final admittance matrix; The multi-machine grid-connected inverter impedance modeling module is used to establish an impedance model for each inverter in the collector line according to the final admittance matrix, establish an equivalent collector line model according to the impedance model, calculate the equivalent high-frequency impedance of each link in the equivalent collector line model, and obtain the multi-machine grid-connected inverter impedance model according to the equivalent high-frequency impedance of each link.

[0036] The division of modules in the embodiments of the present invention is schematic and is only a logical function division. There may be other division methods in actual implementation. In addition, each functional module in each embodiment of the present invention may be integrated into one processor, or may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated modules may be implemented in the form of hardware or in the form of software functional modules.

[0037] In this embodiment, a computer device is also provided, which includes a processor and a memory, wherein the memory is used to store a computer program (in this embodiment, the computer program includes a calculation component and an iteration component, and can perform model calculation and model update), the computer program includes program instructions, and 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 other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of a multi-machine grid-connected inverter impedance modeling method.

[0038] This embodiment also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It can be understood that the computer-readable storage medium here can include both built-in storage media in the computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and 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 processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of a multi-machine grid-connected inverter impedance modeling method in the above embodiment.

[0039] This embodiment further provides a computer program product, which includes a computer program. When the computer program is executed by a processor, the corresponding steps of the impedance modeling method of a multi-machine grid-connected inverter in the above embodiment are implemented.

[0040] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0041] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes 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 a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0042] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0043] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for impedance modeling of a multi-machine grid-connected inverter, characterized in that: The following steps are involved: Based on the frequency coupling effect, the grid-connected inverter impedance modeling is carried out to obtain the final admittance matrix; An impedance model is established for each inverter in the collector line according to the final admittance matrix, an equivalent collector line model is established according to the impedance model, the equivalent high-frequency impedance of each link in the equivalent collector line model is calculated, and the impedance model of the multi-machine grid-connected inverter is obtained according to the equivalent high-frequency impedance of each link.

2. The impedance modeling method of a multi-machine grid-connected inverter according to claim 1, characterized in that: The step of performing grid-connected inverter impedance modeling based on the frequency coupling effect specifically includes: Obtaining the port characteristic expression of the grid-connected inverter based on the frequency coupling relationship; The DC voltage loop, phase-locked loop, current loop and modulation process of the grid-connected inverter are modeled, and the influence of the frequency coupling effect on the grid-connected inverter is analyzed; The final admittance matrix is ​​obtained by combining the port characteristic expression and the influence relationship.

3. The impedance modeling method of a multi-machine grid-connected inverter according to claim 2, characterized in that: The port characteristic expression is as follows (7): （7） in, is the disturbance frequency, In response to the current, is the coupling current, is the disturbance voltage, is the fundamental frequency, is the influence coefficient of positive sequence voltage on positive sequence current response, is the influence coefficient of positive sequence voltage on negative sequence current response, is the influence coefficient of negative sequence voltage on positive sequence current response, is the influence coefficient of negative sequence voltage on negative sequence current response.

4. The impedance modeling method of a multi-machine grid-connected inverter according to claim 3, characterized in that: The influence relationship of the frequency coupling effect on the grid-connected inverter includes: the influence relationship of the disturbance voltage and the response current on the DC bus voltage, the influence relationship of the DC bus voltage and the inverter output voltage, the influence relationship of the disturbance voltage and the response current, and the influence relationship of the disturbance voltage and the inverter port voltage; The influence relationship between the disturbance voltage and the response current on the DC bus voltage is expressed as follows (18): （18） in, It is the equivalent DC current source of the new energy power generation device. represents the DC side capacitance, is the DC side voltage control reference value, is the conjugate of the fundamental frequency current, is the fundamental frequency current, , is the disturbance frequency, is the grid voltage fundamental frequency amplitude, is the filter inductor, and They are the influence matrix coefficients of different corresponding response currents on DC voltage, and They are the influence matrix coefficients of different disturbance voltages on DC voltage; The influence relationship between the DC bus voltage and the inverter output voltage is as follows (19): （19） in, is the fundamental frequency component of the modulated signal, is the conjugate of the fundamental frequency component of the modulating signal, is the transfer function of the DC voltage loop controller, is the transfer function of the d-axis control parameters, and They represent the influence coefficients of different DC bus voltages on the inverter output voltage. is the modulation coefficient; The influence relationship between the disturbance voltage and the response current is as follows (20): （20） in, is the current loop d-axis regulator transfer function, is the current loop q-axis regulator transfer function, , , and They represent the influence matrix coefficients of different disturbance voltages on the response current, is the modulation coefficient, is the decoupling coefficient; The influence relationship between the disturbance voltage and the inverter port voltage is as follows (21): （21） in, , , and They represent the influence matrix coefficients of different disturbance voltages on the inverter port voltage. is the phase-locked loop transfer function.

5. The impedance modeling method of a multi-machine grid-connected inverter according to claim 4, characterized in that: The final admittance matrix is ​​as follows (22): （22） in, and They respectively represent the influence coefficients of different DC bus voltages on the inverter output voltage.

6. The impedance modeling method of a multi-machine grid-connected inverter according to claim 1, characterized in that: The equivalent high-frequency impedance of each link is as follows (25): （25） in, Indicates link x The equivalent impedance of the upper inverter is For Link x The equivalent capacitance to ground between the upper units, For Link x The equivalent impedance between the upper units, Indicates link x The equivalent collector line and unit admittance, Indicates link x The capacitance of the cable line to ground, Indicates link x The impedance of the cable line, For the entire link x The total impedance of 7. A multi-machine grid-connected inverter impedance modeling system, characterized in that: include: Single grid-connected inverter impedance modeling module, used to model the grid-connected inverter impedance based on frequency coupling effect and obtain the final admittance matrix; The multi-machine grid-connected inverter impedance modeling module is used to establish an impedance model for each inverter in the collector line according to the final admittance matrix, establish an equivalent collector line model according to the impedance model, calculate the equivalent high-frequency impedance of each link in the equivalent collector line model, and obtain the multi-machine grid-connected inverter impedance model according to the equivalent high-frequency impedance of each link.

8. A computer device, characterized in that: The invention comprises a memory, a processor and a computer program stored in the memory and executable in the processor, wherein the processor implements the steps of a method for impedance modeling of a multi-machine grid-connected inverter as described in any one of claims 1 to 6 when executing the computer program.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the impedance modeling method for a multi-machine grid-connected inverter described in any one of claims 1 to 6 are implemented.

10. A computer program product, comprising a computer program, characterized in that: When the computer program is executed by a processor, the steps of a method for impedance modeling of a multi-machine grid-connected inverter as described in any one of claims 1 to 6 are implemented.

Images