A multi-machine grid-connected inverter impedance modeling method and related device

Abstract

The application discloses a kind of multi-machine grid-connected inverter impedance modeling method and related equipment, belong to renewable energy power generation field, the method includes the following steps: based on frequency coupling effect grid-connected inverter impedance modeling, obtain final admittance matrix;According to the final admittance matrix, impedance model is established to each inverter in collection line, according to the impedance model, establish equivalent collection line model, calculate the equivalent high-frequency impedance of each link in the equivalent collection line model, according to the equivalent high-frequency impedance of each link, obtain multi-machine grid-connected inverter impedance model.The application can solve the problem that the prior art modeling is not accurate, thereby leading to the problem that stability analysis is not accurate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of renewable energy power generation, and particularly relates to a multi-machine grid-connected inverter impedance modeling method and related equipment. BACKGROUND

[0002] With the continuous development of wind power and photovoltaic power generation and high-voltage AC / DC transmission technology, the weak synchronous grid system dominated by a high proportion of power electronic devices such as wind turbines, photovoltaic stations, high-voltage DC, and reactive power compensation is the main feature of the new energy grid-connected system in China. The complex control of a large number of devices and the characteristics of the weak synchronous grid are intertwined, making the dynamic characteristics of the new energy grid-connected system extremely complex and the stability problem prominent. The impedance analysis method has the advantages of clear physical meaning, intuitive, and measurability, and is currently widely used in stability analysis of new energy grid-connected systems. However, most of the current stability analysis of system models are 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 inaccurate stability analysis. SUMMARY

[0003] The purpose of the present application is to provide a multi-machine grid-connected inverter impedance modeling method and related equipment, which can consider the frequency coupling effect caused by the DC side voltage control loop of the inverter and the multi-machine grid-connected collector line model during stability analysis, solve the problem of inaccurate modeling in the prior art, and thus lead to inaccurate stability analysis.

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0005] In a first aspect, a multi-machine grid-connected inverter impedance modeling method includes the following steps:

[0006] Based on the frequency coupling effect, the grid-connected inverter impedance modeling is performed to obtain a final admittance matrix;

[0007] According to the final admittance matrix, an impedance model is established for each inverter in the collector line, 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 a multi-machine grid-connected inverter impedance model is obtained according to the equivalent high-frequency impedance of each link.

[0008] In some embodiments, the step of performing grid-connected inverter impedance modeling based on the frequency coupling effect specifically includes:

[0009] Based on the frequency coupling relationship, a port characteristic expression of the grid-connected inverter is obtained;

[0010] 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.

[0011] The final admittance matrix is obtained by combining the port characteristic expression and the influence relationship.

[0012] In some embodiments, the port characteristic expression is the following formula (7):

[0013] (7)

[0014] wherein, is a disturbance frequency, is a response current, is a coupling current, is a disturbance voltage, is a fundamental frequency, is an influence coefficient of a positive sequence voltage on a positive sequence current response, is an influence coefficient of a positive sequence voltage on a negative sequence current response, is an influence coefficient of a negative sequence voltage on a positive sequence current response, is an influence coefficient of a negative sequence voltage on a negative sequence current response.

[0015] In some embodiments, the influence relationship of the frequency coupling effect on the grid-connected inverter includes: an influence relationship of a disturbance voltage and a response current on a DC bus voltage, an influence relationship of the DC bus voltage and an inverter output voltage, an influence relationship of the disturbance voltage and the response current, and an influence relationship of the disturbance voltage and an inverter port voltage.

[0016] The influence relationship of the disturbance voltage and the response current on the DC bus voltage is the following formula (18):

[0017] (18)

[0018] wherein, is an equivalent DC current source of a new energy power generation device, denotes a DC side capacitor, is a DC side voltage control reference value, is a conjugate of a fundamental frequency current, is a fundamental frequency current, , is a disturbance frequency, is a grid voltage fundamental frequency amplitude, is a filter inductance, and are influence relationship matrix coefficients of different corresponding response currents on a DC voltage, respectively, and are influence relationship matrix coefficients of different disturbance voltages on the DC voltage, respectively.

[0019] The influence relationship of the DC bus voltage and the inverter output voltage is the following formula (19):

[0020] (19)

[0021] wherein, is a fundamental frequency component of the modulation signal, is a conjugate of the fundamental frequency component of the modulation signal, is a transfer function of the DC voltage loop controller, is a transfer function of the d-axis control parameter, and represent different DC bus voltage to inverter output voltage influence relationship coefficients, respectively, is a modulation coefficient;

[0022] The influence relationship of the disturbance voltage and the response current is formula (20) as follows:

[0023] (20)

[0024] wherein, is a current loop d-axis regulator transfer function, is a current loop q-axis regulator transfer function, and represent different disturbance voltage to response current influence relationship matrix coefficients, respectively, is a modulation coefficient, is a decoupling coefficient;

[0025] The influence relationship of the disturbance voltage and the inverter port voltage is formula (21) as follows:

[0026] (21)

[0027] wherein, and represent different disturbance voltage to inverter port voltage influence relationship matrix coefficients, respectively, is a phase-locked loop transfer function.

[0028] In some embodiments, the final admittance matrix is formula (22) as follows:

[0029] (22)

[0030] wherein, and represent different DC bus voltage to inverter output voltage influence relationship coefficients, respectively.

[0031] ​​​​In some embodiments, the equivalent high-frequency impedance of each link is as follows (25):

[0032] (25)

[0033] wherein, represents the ground capacitance of the link x the equivalent impedance of the upper inverter, is the equivalent ground capacitance between the machine groups, x is the equivalent impedance between the machine groups, represents the equivalent collector line and machine admittance of the link x represents the ground capacitance of the link represents the impedance of the link x cable line, represents the ground capacitance of the link x cable line, represents the impedance of the link x cable line, is the total impedance of the entire link x .

[0034] In a second aspect, a multi-machine grid-connected inverter impedance modeling system comprises:

[0035] a single grid-connected inverter impedance modeling module for modeling the grid-connected inverter impedance based on the frequency coupling effect to obtain a final admittance matrix;

[0036] a multi-machine grid-connected inverter impedance modeling module for establishing an impedance model for each inverter in the collector line according to the final admittance matrix, establishing an equivalent collector line model according to the impedance model, calculating the equivalent high-frequency impedance of each link in the equivalent collector line model, and obtaining a multi-machine grid-connected inverter impedance model according to the equivalent high-frequency impedance of each link.

[0037] 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 executes the computer program to implement the steps of the multi-machine grid-connected inverter impedance modeling method.

[0038] In a fourth aspect, a computer readable storage medium stores a computer program, wherein the computer program is executable in a processor to implement the steps of the multi-machine grid-connected inverter impedance modeling method.

[0039] In a fifth aspect, a computer program product comprises a computer program, wherein the computer program is executable in a processor to implement the steps of the multi-machine grid-connected inverter impedance modeling method.

[0040] Compared with the prior art, the present application has the following beneficial effects:

[0041] The present application provides a multi-machine grid-connected inverter impedance modeling method, which models the grid-connected inverter impedance based on the frequency coupling effect to obtain a final admittance matrix; then, an impedance model of each inverter in the power collection line is established according to the final admittance matrix, an equivalent power collection line model is established according to the impedance model, the equivalent high-frequency impedance of each link in the equivalent power collection 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 application can accurately model the inverter impedance considering the voltage and current closed loop, and the overall model considers the line model of multi-machine grid connection, which is more conducive to accurate stability analysis. The present application establishes a grid-connected inverter impedance model considering the frequency coupling effect, expands the impedance to two dimensions, and is more accurate when analyzing low-frequency stability.

[0042] Further, the present application obtains a 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 a final admittance matrix. Selecting typical control structures such as voltage and current double closed loop, phase-locked loop in synchronous coordinate system, etc., and typical multi-machine model topological structure makes the established multi-machine grid-connected inverter impedance model more universal. The established multi-machine grid-connected inverter impedance model performs equivalent modeling of the power collection line between units in 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 DRAWINGS

[0043] Figure 1 A topological graph of a three-phase grid-connected inverter in the embodiment of the present application;

[0044] Figure 2 A frequency coupling characteristic relationship graph of a three-phase grid-connected inverter in the embodiment of the present application;

[0045] Figure 3 A schematic diagram of an equivalent model of a power collection line in the embodiment of the present application;

[0046] Figure 4 A whole framework schematic diagram of a multi-machine grid-connected inverter impedance modeling method provided by the embodiment of the present application;

[0047] Figure 5 A flowchart schematic diagram of a multi-machine grid-connected inverter impedance modeling method provided by the embodiment of the present application;

[0048] Figure 6This is a structural diagram of an impedance modeling system for a multi-machine grid-connected inverter provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0049] 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 with reference to the accompanying drawings. The content described is intended to explain rather than limit the present invention.

[0050] It should be noted that the terms "including" and "having" and any variations thereof in the description 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.

[0051] like Figure 4 and Figure 5 As shown, this embodiment provides a multi-machine grid-connected inverter impedance modeling method. Based on the modeling using harmonic linearization, the inverter impedance of the voltage and current closed loop can be accurately modeled. The overall model considers the line model of the multi-machine grid, which is more conducive to accurate stability analysis. The method includes the following steps:

[0052] S1, grid-connected inverter impedance modeling considering frequency coupling effect;

[0053] S1.1, Analysis of the generation mechanism of frequency coupling effect of grid-connected inverter. Figure 1 The topology of the three-phase grid-connected inverter under study is shown in the figure. When studying the output impedance, the frequency of the injected current 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 set to , further FFT analysis shows that the same frequency The disturbance current component and frequency are Further research and analysis can derive 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 by PCC is Coupling current , the coupling current The voltage disturbance of the same frequency is generated by the grid impedance , voltage disturbance The coupling frequency is The coupling current forms a cycle.

[0054] Considering that the average model of the grid-connected inverter system can generally be expressed as:

[0055] (1)

[0056] (2)

[0057] 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, 、 、 Represent the three-phase output port voltages of the inverter respectively.

[0058] 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):

[0059] (3)

[0060] (4)

[0061] in, is the initial phase of the positive sequence disturbance voltage, is the initial phase of the 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, is the initial phase of the negative sequence disturbance response current.

[0062] Write (3) (4) in the frequency domain, the expressions are:

[0063] (5)

[0064] (6)

[0065] in, , , , , , .

[0066] 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:

[0067] (7)

[0068] S1.2, Modeling of the DC voltage loop of the grid-connected inverter. Based on the average model of the grid-connected inverter established by equations (1) and (2), substituting (1) into (2) can obtain the expression (8) of the DC bus voltage disturbance component in the frequency domain.

[0069] (8)

[0070] In the formula is the DC side voltage control reference value, is the fundamental frequency current 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 by equation (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. Therefore, the disturbance of the DC side capacitor voltage will also cause a response disturbance component of the output, which can be written as:

[0071] (9)

[0072] 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.

[0073] S1.3, modeling of the phase-locked loop, current loop, and modulation part. Based on 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-locked loop output phase angle disturbance is written as:

[0074] (10)

[0075] in , through convolution operation, we can get The expression is:

[0076] (11)

[0077] Before deriving the current loop model, according to formula (11), the coordinate transformation is obtained d Axis and qThe shaft current will be affected by the disturbance component of the phase-locked loop output angle, and accordingly the expression of the shaft current can be derived d The shaft and q The shaft current frequency domain expression:

[0078] (12)

[0079] (13)

[0080] Where, is the initial phase of the fundamental frequency current.

[0081] According to the control structure of the current loop, the expression of the shaft and d The shaft and q The expression of the disturbance component of the shaft modulation signal needs to be noted that when considering the frequency coupling, considering the asymmetry of the outer loop control structure, the unbalanced current loop control parameters are considered in modeling, that is:

[0082] (14)

[0083] (15)

[0084] Where, is the transfer function of the d-axis regulator of the current loop, is the transfer function of the d-axis control parameter, is the transfer function of the q-axis control parameter.

[0085] Further consider the modulation process, take a phase as an example, considering the time domain expression of the inverter output voltage and the modulation signal (16):

[0086] (16)

[0087] Where, is the time domain component of the a-phase output port voltage of the inverter, is the time domain component of the DC bus voltage, is the time domain component of the a-phase modulation signal of the inverter.

[0088] The frequency domain component of the a-phase output port voltage of the inverter 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:

[0089] (17)

[0090] Where represents the fundamental frequency component of the modulation signal, .

[0091] Based on the above analysis, in order to simplify the final expression, the following groups of expressions are introduced to represent different effects of frequency coupling respectively.

[0092] The influence relationship of the disturbance voltage and the response current on the DC bus voltage can be written as the following matrix expression according to equation (8):

[0093] (18)

[0094] The influence relationship of the DC bus voltage and the inverter output voltage can be written as:

[0095] (19)

[0096] The influence relationship of the disturbance voltage and the response current (affected through the current controller) can be written as:

[0097] (20)

[0098] The influence relationship of the disturbance voltage and the inverter port voltage (affected through the phase-locked loop) can be written as:

[0099] (21)

[0100] After the integration of the three links, the expression form of the admittance matrix is:

[0101] (22)

[0102] S2, considering the collector line model, the impedance modeling of the multi-machine grid-connected inverter is performed;

[0103] 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 equation (22). Since the line model involves high-frequency stability analysis, the impedance model of the inverter can be simplified.

[0104] When the line model is established, the collector line model is first considered. For the collector line between the units on each link, the equivalent is performed by adopting the equal power loss method in the present application, that is, the loss of the equivalent collector line before and after is kept unchanged as the principle, so that Figure 3 The collector line shown in FIG. 8 is taken as an example for the equivalent, and the calculation formula is as follows:

[0105] (23)

[0106] After the equivalent, there is:

[0107] (24)

[0108] 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 equalization, ignoring the voltage difference.

[0109] Comprehensive analysis, for the link x For , the equivalent high-frequency impedance of the link can be obtained after equalization:

[0110] (25)

[0111] In formula (25), Indicates a link x Upper inverter equivalent impedance, For Link x Equivalent capacitance to ground between upper units, For Link x Equivalent impedance between upper units, Indicates a link x The equivalent collector line and unit admittance, Indicates a link x The ground capacitance of the cable line, Indicates a link x The impedance of the cable line can be seen. Equation (25) is calculated twice because the collector line between the units is taken into account. The circuit is equivalent, and the entire link is finally obtained. x The total impedance Finally, the equivalent impedance model of the entire system can be obtained by calculating each link. After considering the high-frequency impedance characteristics of the line, the impedance model is more accurate in the high-frequency band and has full-band accuracy.

[0112] This embodiment provides a multi-machine grid-connected inverter impedance modeling method. By establishing a grid-connected inverter impedance model that considers frequency coupling effects, the impedance is expanded to two dimensions, enabling more accurate analysis of low-frequency stability. Typical control structures (such as a voltage-current dual closed-loop and a synchronous coordinate system phase-locked loop) and typical multi-machine model topologies are selected to make the conclusions more universal. Furthermore, by exploring the equivalent modeling of inter-unit collector lines in multi-machine modeling, the model can also ensure the accuracy of high-frequency stability analysis, making the conclusions more practical.

[0113] like Figure 6 As shown, this embodiment also provides a multi-machine grid-connected inverter impedance modeling system, including:

[0114] 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;

[0115] The multi-machine grid-connected inverter impedance modeling module is configured to model the impedance of each inverter in the collector line according to the final admittance matrix, model the equivalent collector line 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.

[0116] The division of the modules in the embodiments of the present application is illustrative, and is merely a logical functional division. In actual implementation, another division manner can be used. In addition, each functional module in each embodiment of the present application can be integrated in one processor, or can be physically separated, or two or more modules can be integrated in one module. The integrated module can be implemented in the form of hardware or in the form of a software functional module.

[0117] The embodiment also provides a computer device including a processor and a memory. The memory is configured to store a computer program (the computer program includes a calculation component and an iteration component, and is capable of model calculation and model updating). The computer program includes program instructions. The processor is configured to execute the program instructions stored in the computer storage medium. The processor can be a central processing unit (CPU), and can also be another general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or another programmable logic device, a discrete gate or transistor logic device, a discrete hardware component, and the like. The processor is a computing core and a control core of the terminal, and is suitable for implementing one or more instructions. Specifically, the processor is suitable for loading and executing one or more instructions in the computer storage medium to implement a corresponding method flow or a corresponding function. The processor in the embodiment of the present application can be used for the operation of the multi-machine grid-connected inverter impedance modeling method.

[0118] The embodiment further provides a storage medium, specifically a computer readable storage medium (Memory), which is a memory device in a computer device and is used to store programs and data. It can be understood that the computer readable storage medium herein can include an internal storage medium in the computer device, and of course can include an extended storage medium supported by the computer device. The computer readable storage medium provides a storage space, which stores an 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 the instructions can be one or more computer programs (including program codes). It should be noted that the computer readable storage medium herein can be a high-speed RAM memory or a non-volatile memory such as at least one disk memory. The one or more instructions stored in the computer readable storage medium can be loaded and executed by the processor to implement the corresponding steps of the multi-machine grid-connected inverter impedance modeling method in the above embodiment.

[0119] The embodiment further provides a computer program product, which includes a computer program. When the computer program is executed by the processor, the corresponding steps of the multi-machine grid-connected inverter impedance modeling method in the above embodiment are implemented.

[0120] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage, etc.) containing computer-usable program code.

[0121] The present application is described with reference to flowcharts and / or block diagrams of the method, device (system), and computer program product according to the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of the flows and / or blocks in the flowcharts and / or block diagrams 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 produce a device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 Figure 1 The functions specified in one or more flows and / or blocks.

[0122] ​​​​​​These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the flow Figure 1 one or more flows and / or blocks Figure 1 one or more blocks or multiple blocks.

[0123] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the flow Figure 1 one or more flows and / or blocks Figure 1 one or more blocks or multiple blocks.

[0124] Finally, it should be noted that the above-mentioned embodiments are merely used to illustrate the technical solutions of the present application, rather than limiting the same. Even though the present application has been described in detail with reference to the above-mentioned embodiments, those skilled in the art should understand that the specific embodiments of the present application can be modified or replaced equivalently, and any modification or replacement without departing from the spirit and scope of the present application should be covered within the protection scope of the claims of the present application.

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 model is performed to obtain the final admittance matrix; Establishing an impedance model for each inverter in the collector line according to the final admittance matrix, establishing an equivalent collector line model according to the impedance model, calculating the equivalent high-frequency impedance of each link in the equivalent collector line model, and obtaining an impedance model of a multi-machine grid-connected inverter according to the equivalent high-frequency impedance of each link; The step of modeling the grid-connected inverter impedance based on the frequency coupling effect specifically includes: Obtain the port characteristic expression of the grid-connected inverter based on the frequency coupling relationship; Model the DC voltage loop, phase-locked loop, current loop, and modulation process of the grid-connected inverter, and analyze the impact of frequency coupling on the grid-connected inverter. Combining the port characteristic expression and the influence relationship, a final admittance matrix is ​​obtained; The equivalent high-frequency impedance of each link is expressed as follows (25): （25） in, Indicates a link x Upper inverter equivalent impedance, For Link x Equivalent capacitance to ground between upper units, For Link x Equivalent impedance between upper units, Indicates a link x The equivalent collector line and unit admittance, Indicates a link x The ground capacitance of the cable line, Indicates a link x The impedance of the cable line, For the entire link x The total impedance.

2. The impedance modeling method for a multi-machine grid-connected inverter according to claim 1, characterized in that: The port characteristic expression is as follows (7): （7） in, is the disturbance frequency, To respond 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.

3. The impedance modeling method for a multi-machine grid-connected inverter according to claim 2, 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 between the DC bus voltage and the inverter output voltage, the influence relationship between the disturbance voltage and the response current, and the influence relationship between the disturbance voltage and the inverter port voltage; The influence of the disturbance voltage and the response current on the DC bus voltage is expressed in the following equation (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 are the influence matrix coefficients of different corresponding response currents on DC voltage, and 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 expressed 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 expressed as follows (20): （20） in, is the transfer function of the current loop d-axis regulator, is the transfer function of the current loop q-axis regulator, 、 、 and Respectively 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 expressed as follows (21): （21） in, 、 、 and They represent the relationship matrix coefficients of the influence of different disturbance voltages on the inverter port voltage, is the phase-locked loop transfer function.

4. The impedance modeling method for a multi-machine grid-connected inverter according to claim 3, 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.

5. A multi-machine grid-connected inverter impedance modeling system, characterized in that: A multi-machine grid-connected inverter impedance modeling method according to any one of claims 1 to 4, comprising: 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.

6. 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 when the processor executes the computer program, the steps of the impedance modeling method for a multi-machine grid-connected inverter according to any one of claims 1 to 4 are implemented.

7. 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 according to any one of claims 1 to 4 are implemented.

8. A computer program product, comprising a computer program, characterized in that: When the computer program is executed by a processor, the steps of the impedance modeling method for a multi-machine grid-connected inverter according to any one of claims 1 to 4 are implemented.

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