Parameter Design Method and Computer Medium for a Multi-Machine Grid-Connected Inverter Interconnection System

Abstract

The present invention discloses a parameter design method and a computer medium for a multi-machine grid-connected inverter interconnection system. The method includes: S1. Obtain the d-axis current inner-loop control function and the voltage outer-loop control function according to the structure of a single inverter; S2. Configure the parameters of one inverter according to the first method. The first method includes obtaining the current inner-loop and voltage outer-loop control parameters according to the current inner-loop control function and the voltage outer-loop control function under the constraints of a preset bandwidth and phase margin; S3. Configure the parameters of an unconfigured inverter according to the first method in combination with the bandwidth difference constraint and impedance adaptability constraint between inverters; draw the Nyquist curve; S4. Determine whether the Nyquist curve encloses the point (-1, j0). If not, it is determined that the parameter configuration of this inverter is completed; if so, it is determined that this inverter is an unconfigured inverter; after the determination ends, enter S3; S5. When the parameters of all inverters are configured, the parameter design of the system is completed.

Description

Technical Field

[0001] The present invention relates to the field of multi-machine grid-connected inverters, and in particular, to a parameter design method and a computer medium for a multi-machine grid-connected inverter interconnection system. Background Art

[0002] With the continuous increase in the penetration rate of renewable energy in the power grid, distributed power supply systems with grid-connected inverters as the interface, relying on advantages such as high efficiency, fast response, and flexible control, are gradually increasing their application scope. However, due to the uncertainty and volatility of intermittent energy sources, the interaction between multiple inverters and between the multi-inverter system and the power grid is becoming increasingly complex, directly threatening the safe and stable operation of the power grid.

[0003] In a weak power grid, all inverters are coupled through the grid impedance, resulting in mutual influence between inverters and thus affecting the stability of the entire parallel system. At the same time, with the wide connection of inverters, a series of harmonic oscillation and stability problems appear in the distributed system. Considering factors such as inverter grid connection efficiency, new energy grid connection capacity, and renewable energy utilization cost, distributed grid-connected inverters are usually connected in parallel in a series non-isolated structure. This connection method will cause the inverters to be coupled to form a complex high-order electrical network, thereby leading to the interaction of harmonic oscillations between inverters. Such harmonic oscillation phenomena will cause the problem of grid connection instability of the inverters. At the same time, due to factors such as long transmission distance and small short-circuit ratio in the medium and low voltage distribution system of the power grid, the grid impedance is large, which makes the intermittent uncertainty of new energy power generation easily cause voltage fluctuations at the common connection point of the inverters, seriously affecting the normal operation of the inverters in the system, and even causing harmonic oscillations in the entire system when multiple grid-connected inverters are interconnected and operating. In existing research, some scholars have combined the active damping method with dead zone control on the basis of establishing the Norton circuit of the parallel inverter system to solve the harmonic oscillation problem between multiple inverters. However, the effect of dead zone control depends to a large extent on the accuracy of system modeling. But for the sake of simplifying the discussion, the parameters of each inverter are usually set the same, making this method have certain limitations.

[0004] Therefore, there is an urgent need for a new technical solution to solve the technical problem of how to improve the operation stability of a multi-machine grid-connected inverter interconnection system through the parameter design of the inverter. Summary of the Invention

[0005] The present invention provides a parameter design method and a computer medium for a multi-machine grid-connected inverter interconnection system to solve the technical problem of how to improve the operation stability of a multi-machine grid-connected inverter interconnection system through the bandwidth design of the inverter.

[0006] To achieve the above object, the present invention provides a parameter design method for a multi-machine grid-connected inverter interconnection system. The system includes a preset number of grid-following inverters with the same structure and a DC bus voltage control type. The method includes:

[0007] S1. Obtain the current inner-loop control function and voltage outer-loop control function of the d-axis of the inverter according to the structure of a single inverter.

[0008] S2. Configure the parameters of any one inverter according to the first method; the first method includes obtaining the current inner-loop and voltage outer-loop control parameters according to the current inner-loop control function and voltage outer-loop control function under the constraints of a preset bandwidth and phase margin.

[0009] S3. Configure the parameters of any unconfigured inverter according to the first method in combination with the constraints of a preset bandwidth difference between inverters and impedance adaptability constraints; draw the generalized Nyquist curve according to the minimum loop gain matrix of the system at this time.

[0010] S4. Determine whether the generalized Nyquist curve encloses the point (-1, j0). If not, it is determined that the parameter configuration of this inverter is completed; if so, it is determined that this inverter is an unconfigured inverter and the parameters are cleared; after the determination is completed, enter S3.

[0011] S5. When the parameters of all inverters are configured, the parameter design of the multi-machine grid-connected inverter interconnection system is completed.

[0012] Preferably, the current inner-loop control function and voltage outer-loop control function of the d-axis of the inverter include:

[0013] The current inner-loop control function includes the closed-loop transfer function of the current inner-loop :

[0014] ;

[0015] ;

[0016] where represents the open-loop transfer function of the current inner-loop; represents the transfer function of the d-axis current controller; the current inner-loop control parameters include [[ID=4,0]]and ; [[ID=.,43]] represents the proportional coefficient of the transfer function of the d-axis current controller; represents the integral coefficient of the transfer function of the d-axis current controller; represents the Laplace operator; represents the delay transfer function considering the controller delay; represents the transfer function of the main circuit LCL filter;

[0017] The voltage outer-loop control function includes the closed-loop transfer function of the voltage outer-loop :

[0018] ;

[0019] ;

[0020] Among them, represents the open-loop transfer function of the voltage outer-loop; represents the transfer function of the d-axis voltage controller; the voltage outer-loop control parameters include and , represents the proportional coefficient of the transfer function of the d-axis voltage controller; represents the integral coefficient of the transfer function of the d-axis voltage controller; represents the steady-state value of the d-axis of the PCC voltage at the grid connection point; represents the steady-state value of the DC-side output current.

[0021] Preferably, the preset bandwidth and phase margin constraints include:

[0022] The bandwidth constraints include:

[0023] ;

[0024] Among them, represents the cut-off frequency of the open-loop transfer function of the current inner-loop ; represents the voltage outer-loop bandwidth; represents the current inner-loop bandwidth; represents the equivalent switching frequency;

[0025] The phase margin constraints include:

[0026] When configuring the parameters of the inverter, there is a preset positive value for the phase margin of the current inner-loop and the voltage outer-loop.

[0027] Preferably, obtaining the current inner-loop and voltage outer-loop control parameters according to the current inner-loop control function and the voltage outer-loop control function includes:

[0028] A1. Set a set of preset control parameters for the current inner-loop control function and the voltage outer-loop control function. The preset control parameters include , , and preset value combinations;

[0029] A2. Draw the Bode analysis curves of the current inner-loop control function and the voltage outer-loop control function, respectively obtaining the first curve and the second curve; obtain the angular frequencies at -3 dB corresponding to the amplitudes of the first curve and the second curve, respectively obtaining the actual values of the current inner-loop bandwidth and the voltage outer-loop bandwidth;

[0030] A3. Determine whether the actual values of the current inner-loop bandwidth and the voltage outer-loop bandwidth meet the preset bandwidth and phase margin constraints; if they meet, it means that the preset control parameters meet the requirements and are retained as the current inner-loop and voltage outer-loop control parameters; if they do not meet, it means that the preset control parameters do not meet the requirements, and the values of the preset control parameters are adjusted and then enter A2.

[0031] Preferably, the preset inverter - to - inverter bandwidth difference constraint and impedance adaptability constraint include:

[0032] The inverter - to - inverter bandwidth difference constraint includes:

[0033] ;

[0034] Wherein, represents the voltage outer - loop bandwidth of the nth inverter; represents the current inner - loop bandwidth of the nth inverter; the inverter - to - inverter bandwidth difference constraint means that the voltage outer - loop bandwidth and the current inner - loop bandwidth of each inverter in the system need to have a preset difference;

[0035] The impedance adaptability constraint includes: configuring the parameters of the unconfigured inverters under the preset grid impedance.

[0036] Preferably, drawing the generalized Nyquist curve according to the minimum loop gain matrix of the system at this time includes:

[0037] Assume that the total number of inverters in the system, which is the sum of the configured inverters and the unconfigured inverters, is ;

[0038] Select any one of the configured inverters in the system to obtain the equivalent output admittance matrix ; obtain the equivalent output admittance matrices of the remaining all inverters in the system ;

[0039] Obtain the grid impedance equivalent admittance matrix of the system according to the preset grid impedance ;

[0040] According to 、the equivalent output admittance matrices of the remaining all inverters and obtain the minimum loop gain matrix , including:

[0041] ;

[0042] According to the minimum loop gain matrix the generalized Nyquist curve can be plotted.

[0043] The present invention also provides a computer-readable storage medium, on which computer program instructions are stored, and the computer program instructions can be executed by a processor to implement the method of the present invention.

[0044] The present invention has the following beneficial effects:

[0045] The parameter design method of the multi-machine grid-connected inverter interconnection system of the present invention first obtains the current inner-loop control function and voltage outer-loop control function of the d-axis of the inverter according to the structure of a single inverter, providing a basis for the subsequent configuration of the inverter. The current inner-loop control parameters and voltage outer-loop control parameters are obtained through the current inner-loop control function and voltage outer-loop control function, and the initial inverter is configured according to the control parameters, providing a basis for the subsequent configuration of other inverters; at the same time, the preset bandwidth and phase margin constraints are considered when configuring the initial inverter, so that the configured inverter can operate normally. On the basis of the configuration of the initial inverter, further considering the preset bandwidth difference and impedance adaptability constraints between inverters, the unconfigured inverters are configured one by one and verified as a whole, and the effective configuration of all inverter parameters in the system is completed step by step, so that the method of the present invention improves the operation stability of the multi-machine grid-connected inverter interconnection system through the parameter design of the inverter. The method of the present invention improves the operation stability of the multi-machine grid-connected inverter interconnection system by configuring the original inverter parameters in the system, without adding an auxiliary control loop, thereby avoiding the problem of increased cost, and at the same time reducing the cumbersome design process of additionally changing the inverter control structure, and simplifying the system stability improvement process.

[0046] In addition to the purposes, features and advantages described above, the present invention has other purposes, features and advantages. The following will refer to the drawings to further elaborate on the present invention in detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0048] Figure 1 is the structure and control schematic diagram of the DC bus voltage controlled grid-following inverter of the preferred embodiment of the present invention.

[0049] Figure 2 is the schematic diagram of the multi-machine grid-connected inverter interconnection system of the preferred embodiment of the present invention.

[0050] Figure 3 It is a schematic diagram of a method flow of a preferred embodiment of the present invention.

[0051] Figure 4 It is a schematic diagram of the generalized Nyquist curve of the system when the grid impedance is 7.5mH according to the preferred embodiment of the present invention.

[0052] Figure 5 It is a schematic diagram of the generalized Nyquist curve of the system when the grid impedance is 8.5mH according to a preferred embodiment of the present invention.

[0053] Figure 6 1 is a schematic diagram of the output waveform of the system when the grid impedance is 7.5 mH according to a preferred embodiment of the present invention.

[0054] Figure 7 1 is a schematic diagram of the output waveform of the system when the grid impedance is 8.5mH according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0055] 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.

[0056] See also Figure 1 The DC bus voltage controlled grid-following inverter of the present invention comprises: a DC bus capacitor , three-phase inverter, inductor and ,capacitance and series damping resistor ;in 、 and Construct an LCL filter.

[0057] See also Figure 1 In the DC bus voltage controlled grid-following inverter of the present invention, from left to right, the DC power supply Through the DC bus capacitor Maintain the stability of the DC side voltage of the inverter, and then transmit it to the AC circuit through the three-phase inverter to form a three-phase AC voltage The harmonics generated by the inverter are filtered out through the LCL filter circuit to obtain high-quality grid-connected current, and finally connected to the grid through the public grid connection point.

[0058] See also Figure 1 The control principle of the DC bus voltage controlled grid-following inverter of the present invention includes: in order to maintain the DC bus capacitance Voltage stability, extract its voltage Used to control the circuit as feedback real signal for control, and After taking the difference, it passes through a voltage controller to obtain the d-axis current reference value , and takes the difference with the true value of the d-axis extracted current and passes through the current controller to obtain the d-axis voltage modulation signal of the inverter ; the q-axis current reference value takes the difference with the true value of the q-axis extracted current and passes through the current controller to obtain the q-axis voltage modulation signal of the inverter ; finally, based on the voltage modulation signal, the three-phase inverter is controlled by the PWM modulation method to realize the operation of the inverter.

[0059] In Figure 1 , and respectively represent the DC-side capacitor voltage and the output current; represents the output current on the inverter side; represents the grid-side current; represents the voltage at the point of common coupling; represents the grid impedance; represents the grid equivalent voltage source; represents the output phase angle of the phase-locked loop PLL; represents the voltage reference value signal; and respectively represent the d-axis and q-axis reference value signals of the current ; is the modulation gain; and represent the voltage modulation signal; represents the DC power supply current; represents the voltage at the output port of the inverter; and represent the actual values of the inverter output current; PCC represents the point of common coupling of the inverter; abc / dq represents the dq transformation; dq / abc represents the inverse dq transformation.

[0060] In the multi-machine grid-connected inverter interconnection system of the present invention, the inverters are connected in parallel, and the structural schematic diagram of the system is shown in Figure 2 .

[0061] See Figure 3 , in the preferred embodiment of the present invention, a parameter design method for a multi-machine grid-connected inverter interconnection system is provided. The system includes a preset number of grid-following inverters with the same structure of DC bus voltage control. The method includes:

[0062] S1. Obtain the current inner-loop control function and voltage outer-loop control function of the d-axis of the inverter according to the structure of a single inverter.

[0063] In the preferred embodiment S1 of the present invention, the current inner loop control function and voltage outer loop control function of the inverter include:

[0064] The current inner loop control function includes the closed-loop transfer function of the current inner loop :

[0065] ;

[0066] ;

[0067] Among them, represents the open-loop transfer function of the current inner loop; represents the transfer function of the d-axis current controller; the current inner loop control parameters include and , represents the proportional coefficient of the transfer function of the d-axis current controller; represents the integral coefficient of the transfer function of the d-axis current controller; represents the Laplace operator; represents the delay transfer function considering the controller delay; represents the transfer function of the main circuit LCL filter;

[0068] The voltage outer loop control function includes the closed-loop transfer function of the voltage outer loop :

[0069] ;

[0070] ;

[0071] Among them, represents the open-loop transfer function of the voltage outer loop; represents the transfer function of the d-axis voltage controller; the voltage outer loop control parameters include and , represents the proportional coefficient of the transfer function of the d-axis voltage controller; represents the integral coefficient of the transfer function of the d-axis voltage controller; represents the steady-state value of the d-axis of the point of common coupling (PCC) voltage; represents the steady-state value of the DC side output current.

[0072] S2. Configure the parameters of any inverter according to the first method; the first method includes obtaining the current inner loop and voltage outer loop control parameters according to the current inner loop control function and voltage outer loop control function under the constraints of a preset bandwidth and phase margin.

[0073] In S2 of the preferred embodiment of the present invention, the constraints of the preset bandwidth and phase margin include:

[0074] The bandwidth constraints include:

[0075] ;

[0076] Among them, represents the cut-off frequency of the open-loop transfer function of the inner current loop ; represents the bandwidth of the outer voltage loop; represents the bandwidth of the inner current loop; represents the equivalent switching frequency;

[0077] The phase margin constraints include:

[0078] When configuring the parameters of the inverter, there are preset positive values for the phase margins of the inner current loop and the outer voltage loop.

[0079] In S2 of the preferred embodiment of the present invention, obtaining the control parameters of the inner current loop and the outer voltage loop according to the inner current loop control function and the outer voltage loop control function includes:

[0080] A1. Set a set of preset control parameters for the inner current loop control function and the outer voltage loop control function. The preset control parameters include , , and preset value combinations;

[0081] A2. Plot the bode analysis curves of the inner current loop control function and the outer voltage loop control function to obtain the first curve and the second curve respectively; obtain the angular frequencies at -3dB corresponding to the amplitudes of the first curve and the second curve to obtain the actual values of the bandwidths of the inner current loop and the outer voltage loop respectively;

[0082] A3. Determine whether the actual values of the bandwidths of the inner current loop and the outer voltage loop meet the preset bandwidth and phase margin constraints; if they meet, it means that the preset control parameters meet the requirements and are retained as the control parameters of the inner current loop and the outer voltage loop; if they do not meet, it means that the preset control parameters do not meet the requirements, and the values of the preset control parameters are adjusted and then enter A2.

[0083] S3. Configure the parameters of any unconfigured inverter according to the first method in combination with the preset bandwidth difference constraint and impedance adaptability constraint between inverters; draw the generalized Nyquist curve according to the minimum loop gain matrix of the system at this time.

[0084] In S3 of the preferred embodiment of the present invention, the preset bandwidth difference constraint and impedance adaptability constraint between inverters include:

[0085] The bandwidth difference constraint between inverters includes:

[0086] ;

[0087] Among them, represents the voltage outer loop bandwidth of the nth inverter; represents the current inner loop bandwidth of the nth inverter; the bandwidth difference constraint between inverters means that the voltage outer loop bandwidth and the current inner loop bandwidth of each inverter in the system need to be constrained to have a preset difference;

[0088] The impedance adaptability constraint includes: configuring parameters for the unconfigured inverters under the preset grid impedance.

[0089] In S3 of the preferred embodiment of the present invention, drawing the generalized Nyquist curve according to the minimum loop gain matrix of the system at this time includes:

[0090] Assume that the sum of the configured inverters and the unconfigured inverters in the system, that is, the total number of inverters, is ;

[0091] Select any one from the inverters with configured parameters in the system to obtain the equivalent output admittance matrix ; Obtain the equivalent output admittance matrices of all the remaining inverters in the system ;

[0092] Obtain the grid impedance equivalent admittance matrix of the system according to the preset grid impedance ;

[0093] According to , all the remaining inverters' equivalent output admittance matrices and to obtain the minimum loop gain matrix , including:

[0094] ;

[0095] According to the minimum loop gain matrix , the generalized Nyquist curve can be drawn.

[0096] S4. Judge whether the generalized Nyquist curve encloses the point (-1, j0). If not, it is determined that the parameter configuration of this inverter is completed; if so, it is determined that this inverter is an unconfigured inverter and the parameters are cleared; after the determination, enter S3.

[0097] S5. When the parameters of all inverters are configured, the parameter design of the multi-machine grid-connected inverter interconnection system is completed.

[0098] The parameter design method of the multi-inverter parallel-connected inverter interconnection system of the present invention first obtains the current inner-loop control function and voltage outer-loop control function of the d-axis of the inverter according to the structure of a single inverter, providing a basis for the subsequent configuration of the inverter. The current inner-loop and voltage outer-loop control parameters are obtained through the current inner-loop control function and voltage outer-loop control function, and the initial inverter is configured according to the control parameters, providing a basis for the subsequent configuration of other inverters; at the same time, the preset bandwidth and phase margin constraints are considered when configuring the initial inverter, so that the configured inverter can operate normally. On the basis of the configuration of the initial inverter, further considering the preset bandwidth difference and impedance adaptability constraints between inverters, the unconfigured inverters are configured one by one and verified as a whole, and the effective configuration of all inverter parameters in the system is completed step by step, so that the method of the present invention improves the operation stability of the multi-inverter parallel-connected inverter interconnection system through the parameter design of the inverter. The method of the present invention improves the operation stability of the multi-inverter parallel-connected inverter interconnection system by configuring the original inverter parameters in the system, without adding an auxiliary control loop, thus avoiding the problem of increased cost, and at the same time reducing the cumbersome design process of additionally changing the inverter control structure and simplifying the system stability improvement process.

[0099] In a preferred embodiment of the present invention, there is also provided a computer-readable storage medium on which computer program instructions are stored, and the computer program instructions can be executed by a processor to implement the method of the present invention.

[0100] Verification part:

[0101] In a preferred embodiment of the present invention, a set of two DC bus voltage-controlled grid-following inverter interconnection systems is built in MATLAB / Simulink, and the simulation parameters are shown in Table 1:

[0102] Table 1 Simulation parameters

[0103] ;

[0104] To verify the effectiveness of the method of the present invention, Figures 4 to 5 the generalized Nyquist analysis results of the final parameter setting using the method of the present invention are given. Figures 6 to 7 The operation simulation results of the multi-inverter system under different grid impedances are given.

[0105] In Figures 4 to 5 the blue curve represents the generalized Nyquist curve with an eigenvalue of 1; the purple curve represents the generalized Nyquist curve with an eigenvalue of 2; the red curve represents the unit circle used to find the (-1, j0) point.

[0106] Figure 4Shows the plotting results of the generalized Nyquist criterion of the multi-inverter system when the grid impedance is set to 7.5 mH. At this time, the generalized Nyquist curve does not enclose the point (-1, j0), and the system output wave remains stable.

[0107] Figure 5 Shows the plotting results of the generalized Nyquist criterion of the multi-inverter system when the grid impedance is set to 8.5 mH. At this time, the generalized Nyquist curve encloses the point (-1, j0), and the system output wave becomes unstable. In this simulation, 7.5 mH is set as the impedance adaptation target of this multi-inverter system. The method of the present invention can effectively set the parameters of each inverter in the system, and realize the effective determination of the generalized Nyquist criterion for the target-adapted grid impedance of 7.5 mH.

[0108] See Figure 6 , when the system parameters are designed by the method of the present invention, the system output waveform remains stable when the grid impedance reaches 7.5 m; see Figure 7 When the grid impedance increases to 8.5 mH, the system loses stability, successfully verifying the effectiveness of the parameter design of the present invention. Figures 6 to 7 in , and respectively represent the a, b, and c phase currents of the inverters configured this time.

[0109] The above analysis results verify the correctness and effectiveness of the method of the present invention, can effectively optimize the control bandwidth of each inverter in the multi-inverter system, and provide direct theoretical guidance for the safe and stable operation of the power grid.

[0110] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A parameter design method for a multi-machine grid-connected inverter interconnection system, the system comprising a preset number of grid-following inverters with the same structure and DC bus voltage control, characterized in that, The method includes: S1. Obtain the current inner-loop control function and voltage outer-loop control function of the d-axis of the inverter according to the structure of a single inverter; S2. Configure the parameters of any inverter according to the first method; the first method includes obtaining the current inner-loop and voltage outer-loop control parameters according to the current inner-loop control function and voltage outer-loop control function under the constraints of a preset bandwidth and phase margin, including: A1. Set a set of preset control parameters for the current inner-loop control function and the voltage outer-loop control function, where the preset control parameters include the current inner-loop control parameters k pi and k ii as well as the voltage outer-loop control parameters k pv and k iv for the preset value combinations; A2. Plot the bode analysis curves of the current inner-loop control function and voltage outer-loop control function to obtain a first curve and a second curve respectively; obtain the angular frequencies at -3dB corresponding to the amplitudes of the first curve and the second curve to obtain the actual values of the current inner-loop bandwidth and voltage outer-loop bandwidth respectively; A3. Determine whether the actual values of the current inner-loop bandwidth and voltage outer-loop bandwidth meet the preset bandwidth and phase margin constraints; if they meet, it means that the preset control parameters meet the requirements and are retained as the current inner-loop and voltage outer-loop control parameters; if they do not meet, it means that the preset control parameters do not meet the requirements, and the values of the preset control parameters are adjusted and then enter A2; S3. Configure the parameters of any unconfigured inverter according to the first method in combination with the preset bandwidth difference constraint and impedance adaptability constraint between inverters; draw a generalized Nyquist curve according to the minimum loop gain matrix of the system at this time; S4. Determine whether the generalized Nyquist curve encloses the point (-1, j0); if not, it is determined that the parameter configuration of this inverter is completed; if so, it is determined that this inverter is an unconfigured inverter and the parameters are cleared; after the determination, enter S3; S5. When the parameters of all inverters are configured, the parameter design of the multi-machine grid-connected inverter interconnection system is completed.

2. The parameter design method of the multi-machine grid-connected inverter interconnection system according to claim 1, characterized in that The current inner-loop control function and voltage outer-loop control function of the d-axis of the inverter include: The current inner loop control function includes the closed-loop transfer function of the current inner loop : ； ； Among them, represents the open-loop transfer function of the inner current loop; represents the transfer function of the d-axis current controller; the control parameters of the inner current loop include and , represents the proportional coefficient of the transfer function of the d-axis current controller; represents the integral coefficient of the transfer function of the d-axis current controller; represents the Laplace operator; represents the delay transfer function considering the controller delay; represents the transfer function of the main circuit LCL filter; The voltage outer-loop control function includes the closed-loop transfer function of the voltage outer loop : ； ； Among them, represents the open-loop transfer function of the voltage outer loop; represents the transfer function of the d-axis voltage controller; the voltage outer loop control parameters include and , represents the proportional coefficient of the transfer function of the d-axis voltage controller; represents the integral coefficient of the transfer function of the d-axis voltage controller; represents the steady-state value of the d-axis of the point of common coupling (PCC) voltage; represents the steady-state value of the DC side output current.

3. The parameter design method of the multi-machine grid-connected inverter interconnection system according to claim 2, characterized in that The preset bandwidth and phase margin constraints include: The bandwidth constraint includes: ； Among them, represents the cut-off frequency of the open-loop transfer function of the inner current loop ; represents the bandwidth of the outer voltage loop; represents the bandwidth of the inner current loop; represents the equivalent switching frequency; The phase margin constraint includes: When configuring the parameters of the inverter, there is a preset positive value for the phase margin of the current inner-loop and voltage outer-loop.

4. The parameter design method of the multi-machine grid-connected inverter interconnection system according to claim 3, wherein The preset bandwidth difference constraint and impedance adaptability constraint between inverters include: The bandwidth difference constraint between inverters includes: ； Among them, represents the voltage outer-loop bandwidth of the nth inverter; represents the current inner-loop bandwidth of the nth inverter; the bandwidth difference constraint between inverters means that the voltage outer-loop bandwidth and the current inner-loop bandwidth of each inverter in the system need to be constrained to have a preset difference; The impedance adaptability constraint includes: configuring the parameters of the unconfigured inverter under the preset grid impedance.

5. The parameter design method of the multi-machine grid-connected inverter interconnection system according to claim 4, characterized in that Drawing a generalized Nyquist curve according to the minimum loop gain matrix of the system at this time includes: Suppose the sum of the inverters with parameter configuration and those without configuration in the system, i.e., the total number of inverters, is ; Select any one of the inverters with parameter configuration completed within the system to obtain the equivalent output admittance matrix ; Obtain all the remaining equivalent output admittance matrices of the inverters ; Obtain the equivalent admittance matrix of the power grid impedance of the system according to the preset power grid impedance ; According to , all the remaining equivalent output admittance matrices of the inverters and obtain the minimum loop gain matrix , including: ； According to the minimum loop gain matrix the generalized Nyquist curve can be plotted.

6. A computer-readable storage medium, on which computer program instructions are stored, and the computer program instructions can be executed by a processor to implement the method according to any one of claims 1 to 5.

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