Sequence immittance modeling and stability analysis method for heterogeneous new energy grid-connected power system

Abstract

The invention discloses a sequence immittance modeling and stability analysis method for a heterogeneous new energy grid-connected power system, and belongs to the technical field of power system control, and the method comprises the steps: carrying out the two-port equivalence of each converter in the heterogeneous new energy grid-connected power system, and adding voltage disturbance to an AC port and a DC port; further modeling respective control rings and nonlinear circuits of various converters under current response of voltage disturbance to obtain an initial transfer function of a sequence immittance model corresponding to each frequency coupling component, fully considering the interaction between the following / constructing network type converters, revealing the frequency coupling rule of the converters, and improving the reliability of the converter. The accuracy of the sequence immittance model is improved; and correcting the initial transfer function of the sequence immittance model corresponding to each frequency coupling component by using the corrected sequence immittance circuit equation to obtain the corrected transfer function of the sequence immittance model of each frequency coupling component, and accurately carrying out linear modeling on the sequence immittance of the heterogeneous new energy grid-connected power system.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system control, and more specifically, relates to a sequence impedance modeling and stability analysis method for a heterogeneous renewable energy grid-connected power system. Background Art

[0002] With the rapid development of new energy power generation technology, the proportion of new energy power electronic power sources in my country's power installed capacity continues to rise. Therefore, the grid-connected performance requirements of new energy stations are also gradually increasing. At present, most of the new energy controls connected to the power grid adopt grid-following control, which relies on traditional synchronous generators to provide a stable voltage source. It is difficult to adapt to the future grid scenario with a high proportion of new energy connected to the grid. Heterogeneous new energy grid-connected power systems are connected to grid-following converters and grid-connecting converters.

[0003] For heterogeneous renewable energy grid-connected power systems, traditional small signal modeling methods are difficult to directly perform linear modeling; if a synchronous rotating coordinate is fictitious for small signal linear modeling, the physical meaning of the model will become blurred. At present, there are great difficulties in the stability analysis of heterogeneous renewable energy systems. The existing methods are mainly based on the aggregation of renewable energy single machines, lacking the detailed process inside renewable energy and the modeling of heterogeneous multi-machine renewable energy grid-connected systems under the influence of system parameters. It is difficult to reveal the internal stability by analyzing the stability of multi-machine grid-connected systems with aggregation models. At present, the methods of multi-machine aggregation are divided into two aspects: dq impedance aggregation and sequence impedance aggregation. In dq axis impedance aggregation, it is necessary to obtain the steady-state operating point phase angle under all dq modeling phase angles to obtain the phase angle conversion matrix, which is very difficult for actual system applications. In addition, the aggregation based on sequence impedance has not yet considered the stability between the units inside the system, but only focuses on the stability of the grid connection point, which poses a challenge to the stability analysis of heterogeneous renewable energy grid-connected systems. In addition, there are also methods of using direct matrix calculation in large systems, but it is difficult to obtain the network matrix of the entire system to directly judge the stability in today's large systems. Therefore, this idea needs to be further simplified and cannot be directly applied.

[0004] In summary, the adaptability of converters to the stability of strong and weak grids is of universal and critical significance for the reliable operation and absorption of large-scale renewable energy access. It is urgent to further explore the modeling and analysis methods of multi-station stability when multiple converters are connected to the grid. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a sequence impedance modeling and stability analysis method for a heterogeneous renewable energy grid-connected power system, which aims to solve the technical problem that traditional modeling methods are difficult to directly perform linear modeling of a heterogeneous renewable energy grid-connected power system with low computational complexity and high accuracy.

[0006] To achieve the above object, according to one aspect of the present invention, a sequence immittance modeling method for a heterogeneous renewable energy grid-connected power system is provided, comprising:

[0007] S1: Perform two-port equivalence on the grid-following converter and the grid-forming converter in the heterogeneous renewable energy grid-connected power system to obtain a two-port network corresponding to the grid-following converter and the grid-forming converter respectively; the two-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; add voltage disturbances to the AC port and the DC port to obtain a current response to the voltage disturbance;

[0008] S2: performing sequence immittance modeling on the control loops of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance to obtain a sequence immittance model of the grid-following control loop and a sequence immittance model of the grid-forming control loop;

[0009] S3: performing frequency AC / DC coupling analysis on the nonlinear circuits of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance to obtain multiple frequency coupling components; modeling the initial transfer function of the sequence immittance model corresponding to each frequency coupling component;

[0010] S4: combining the circuit equation of the nonlinear circuit with the sequence immittance model of the grid-following control loop and the control equation of the sequence immittance model of the grid-forming control loop, removing the zero-sequence component in the circuit equation, and obtaining a corrected sequence immittance circuit equation;

[0011] S5: using the modified sequence immittance circuit equation to modify the initial transfer function of the sequence immittance model corresponding to each frequency coupling component, to obtain the modified transfer function of the sequence immittance model corresponding to each frequency coupling component.

[0012] In one embodiment, the synchronous control model in the control loop of the grid-following converter and the grid-forming converter is:

[0013]

[0014] in, is the phase angle in the frequency domain, J is the inertia coefficient of the virtual synchronous control loop, D p is the damping coefficient of the virtual synchronous control loop, is the voltage disturbance applied to the AC port, is the current disturbance after the voltage disturbance added to the AC port, ω0 is the initial rotation angular velocity, ω1 is the fundamental frequency, U1 * 、I1 * are the conjugates of the initial phasors of voltage and current, respectively.

[0015] In one embodiment,

[0016] Using the formula Modeling the initial transfer function of the sequence immittance model corresponding to each frequency coupling component;

[0017] Among them, x(t) is the time domain value of the x variable, y(t) is the time domain value of the y variable, is the steady-state value of the x variable at the steady-state operating point, is the superimposed small signal value under small perturbation of x variable, is the steady-state value of the y variable at the steady-state operating point, is the superimposed small signal value under small disturbance of y variable, is the small signal value after the harmonic linearization of Z(t), is the superimposed small signal value under the small disturbance of the y variable, Y l is the steady-state value of the y variable at the steady-state operating point, where l is used to represent the number of components of the y variable itself, X k is the steady-state value of the variable at the steady-state operating point, is the superimposed small signal value under small perturbation of the variable, where k is used to represent the number of components of the x variable itself; ω p is the disturbance frequency, ω1 is the fundamental frequency, is the kth harmonic component of the x variable, is the kth harmonic component of Y.

[0018] In one embodiment, when a positive sequence voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is:

[0019]

[0020] Among them, Y pp (s) is the positive sequence response self-admittance under positive sequence voltage disturbance, Y pd (s) is the AC-DC coupled admittance of the DC response under positive sequence voltage disturbance, Y pn (s) is the negative sequence response AC transfer admittance under positive sequence voltage disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0021] In one embodiment, when a negative sequence voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is:

[0022]

[0023] Among them, Y nn (s) is the positive sequence response self-admittance under negative sequence voltage disturbance, Y nd (s) is the AC-DC coupled admittance of the DC response under negative sequence voltage disturbance, Y np (s) is the negative sequence response AC transfer admittance under negative sequence voltage disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0024] In one embodiment, when a DC voltage disturbance is added to the DC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is:

[0025]

[0026] Among them, Y dd (s) is the DC response self-admittance under DC disturbance, Y dp (s) is the AC-DC coupled admittance of the AC positive sequence response under DC disturbance, Y pn (s) is the AC transfer admittance of the AC negative sequence response under DC disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0027] In one embodiment, the modified transfer function of the grid-following converter is expressed as:

[0028]

[0029] in, is the response current of the AC port, is the voltage disturbance of the AC port, L is the AC inductance, K d is the feedback coefficient of the inner current loop, V dc Represents the DC voltage value, H c (s-jω1) represents the transfer function of the inner current loop, is the fundamental frequency parameter of the modulation signal, The parameter representing the fundamental frequency of the current, represents the conjugate complex number of the fundamental voltage complex number, ω0 represents the base frequency value, G θ (s-jω1) is the closed-loop transfer function of the phase-locked loop, H va (s-jω1) is the transfer function of the AC voltage outer loop, Hc (s-jω1) is the transfer function of the inner current loop, represents the fundamental complex number of admittance, s represents the Laplace factor, and j represents the 90-degree rotation component in the complex frequency domain.

[0030] In one embodiment, the modified transfer function of the grid-connected converter is expressed as:

[0031]

[0032] Where, L is the AC inductance, K d is the feedback coefficient of the inner current loop, V dc Represents the DC voltage value, H c (s-jω1) represents the transfer function of the inner current loop, is the fundamental frequency parameter of the modulation signal, The parameter representing the fundamental frequency of the current, represents the conjugate complex number of the fundamental current complex number, represents the conjugate complex number of the fundamental voltage complex number, ω0 represents the base frequency value, is the response current of the AC port, H c (s-jω1) is the transfer function of the inner current loop, is the voltage disturbance of the AC port, and M(s-jω1) represents the transfer function of the virtual synchronous control loop.

[0033] According to another aspect of the present invention, a sequence impedance modeling device for a heterogeneous renewable energy grid-connected power system is provided, comprising:

[0034] A disturbance module is used to perform two-port equivalence on a grid-following converter and a grid-forming converter in a heterogeneous renewable energy grid-connected power system to obtain a two-port network corresponding to the grid-following converter and the grid-forming converter respectively; the two-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; a voltage disturbance is added to the AC port and the DC port to obtain a current response to the voltage disturbance;

[0035] A first modeling module is used to perform sequence immittance modeling on the control loops of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance, so as to obtain a sequence immittance model of the grid-following control loop and a sequence immittance model of the grid-forming control loop;

[0036] The second modeling module is used to perform frequency AC / DC coupling analysis on the nonlinear circuits of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance to obtain multiple frequency coupling components; and to model the initial transfer function of the sequence immittance model corresponding to each frequency coupling component;

[0037] A first correction module is used to combine the circuit equation of the nonlinear circuit with the control equations of the sequence immittance model of the grid-following control loop and the sequence immittance model of the grid-forming control loop, remove the zero-sequence component in the circuit equation, and obtain a corrected sequence immittance circuit equation;

[0038] The second correction module is used to correct the initial transfer function of the sequence immittance model corresponding to each frequency coupling component by using the corrected sequence immittance circuit equation to obtain the corrected transfer function of the sequence immittance model corresponding to each frequency coupling component.

[0039] According to another aspect of the present invention, a stability analysis method for a heterogeneous renewable energy grid-connected power system is provided, comprising:

[0040] The modified transfer function of the sequence immittance model of each frequency coupling component is constructed by using the sequence immittance modeling method of the heterogeneous renewable energy grid-connected power system.

[0041] Using the modified transfer function, the impedance modeling is performed on the grid side to which the grid-following converter and the grid-forming converter are connected, so as to obtain the original grid network without the converter connected;

[0042] A stability analysis is performed on the original power grid network, the grid-type converter and the grid-forming converter respectively. If they are all stable, the grid-forming converter is connected to the original power grid network to determine whether the power system is stable. If it is unstable, it is regarded as the power system instability caused by the grid-forming converter. If it is stable, the grid-forming converter is connected to the network after the grid-forming converter is connected to the original power grid network to determine whether the power system is stable. If it is unstable, it is regarded as the power system instability caused by the grid-forming converter.

[0043] According to another aspect of the present invention, a stability analysis device for a heterogeneous renewable energy grid-connected power system is provided, comprising:

[0044] A disturbance module is used to perform two-port equivalence on a grid-following converter and a grid-forming converter in a heterogeneous renewable energy grid-connected power system to obtain a two-port network corresponding to the grid-following converter and the grid-forming converter respectively; the two-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; a voltage disturbance is added to the AC port and the DC port to obtain a current response to the voltage disturbance;

[0045] A first modeling module is used to perform sequence immittance modeling on the control loops of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance, so as to obtain a sequence immittance model of the grid-following control loop and a sequence immittance model of the grid-forming control loop;

[0046] The second modeling module is used to perform frequency AC / DC coupling analysis on the nonlinear circuits of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance to obtain multiple frequency coupling components; and to model the initial transfer function of the sequence immittance model corresponding to each frequency coupling component;

[0047] A first correction module is used to combine the circuit equation of the nonlinear circuit with the control equations of the sequence immittance model of the grid-following control loop and the sequence immittance model of the grid-forming control loop, remove the zero-sequence component in the circuit equation, and obtain a corrected sequence immittance circuit equation;

[0048] A second correction module is used to correct the initial transfer function of the sequence immittance model corresponding to each frequency coupling component by using the corrected sequence immittance circuit equation to obtain a corrected transfer function of the sequence immittance model corresponding to each frequency coupling component;

[0049] A judgment module is used to use the modified transfer function to perform impedance modeling on the grid side to which the grid-following converter and the grid-forming converter are connected, so as to obtain an original grid network without the converter connected; respectively perform stability analysis on the original grid network, the grid-following converter and the grid-forming converter; if all are stable, connect the grid-forming converter to the original grid network to determine whether the power system is stable; if not, it is regarded as the instability of the power system caused by the grid-forming converter; if stable, connect the grid-following converter to the network after the grid-forming converter is connected to the original grid network to determine whether the power system is stable; if not, it is regarded as the instability of the power system caused by the grid-following converter.

[0050] According to another aspect of the present invention, there is provided an electronic device including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the sequence impedance modeling method or the stability analysis method for the heterogeneous new energy grid-connected power system are implemented.

[0051] According to another aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored, and when the processor executes the computer program, the steps of the sequence impedance modeling method or stability analysis method of the above-mentioned heterogeneous new energy grid-connected power system are implemented.

[0052] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0053] (1) The present invention provides a sequence impedance modeling method for a heterogeneous renewable energy grid-connected power system, which performs two-port equivalence on various converters in the heterogeneous renewable energy grid-connected power system and adds voltage disturbances to the AC port and the DC port; further, the control loops and nonlinear circuits of various converters under the current response of the voltage disturbance are modeled to obtain the initial transfer function of the sequence impedance model corresponding to each frequency coupling component, fully consider the interaction between the grid-connected / connected converters, reveal the frequency coupling law of the converters, and improve the accuracy of the sequence impedance model; further, the initial transfer function of the sequence impedance model corresponding to each frequency coupling component is corrected by using the corrected sequence impedance circuit equation to obtain the corrected transfer function of the sequence impedance model of each frequency coupling component, so as to accurately perform linear modeling on the sequence impedance of the heterogeneous renewable energy grid-connected power system.

[0054] (2) In this scheme, the virtual synchronous control model in the control loop of the grid-following converter and the grid-forming converter is: It considers the two main power sources of heterogeneous renewable energy grid-connected systems, grid-following converters and grid-forming converters. It also considers the effect of frequency domain phase angle under the frequency coupling of grid-following control and grid-forming control. Compared with the existing renewable energy grid-connected analysis, it can be used to fully consider the stability of heterogeneous stations composed of grid-following converters and grid-forming converters.

[0055] (3) This scheme uses The initial transfer function of the sequence impedance model corresponding to each frequency coupling component is modeled; it takes into account the feedback coupling of the converter DC system and the effect of frequency coupling. Compared with the existing sequence impedance modeling, this method defines the influence of a total of 9 functions. Compared with the traditional two functions and four transfer functions, it can more comprehensively explain the transfer function influence mechanism of the sequence impedance of the grid-type control, and explain the role of impedance modeling.

[0056] (4) In this scheme, when the positive sequence voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is: It takes into account the coupling feedback effect on the grid side and the feedback loop effect on the DC side. Compared with the existing sequence impedance modeling, it can more comprehensively reflect the interactive influence relationship between the converter control and the circuit, and improve the frequency domain modeling accuracy of the positive-sequence impedance in the low-frequency band.

[0057] (5) In this scheme, when a negative sequence voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is: It takes into account the coupling feedback effect on the grid side and the feedback loop effect on the DC side. Compared with the existing sequence impedance modeling, it can more comprehensively reflect the interactive influence relationship between the converter control and the circuit, and improve the frequency domain modeling accuracy of negative sequence impedance in the low frequency band.

[0058] (6) In this scheme, when a DC voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is: It takes into account the AC / DC coupling characteristics of the converter and can improve the modeling accuracy of DC impedance compared with the existing sequence impedance modeling.

[0059] (7) The modified transfer function of the grid-connected converter described in this scheme is expressed as: The zero-sequence variables of the circuit are removed, and the accuracy is higher.

[0060] (8) This scheme provides a sequence impedance modeling device for a heterogeneous renewable energy grid-connected power system. The device performs two-port equivalence on various converters in the heterogeneous renewable energy grid-connected power system and adds voltage disturbances to the AC port and the DC port. The device further models the control loops and nonlinear circuits of various converters under the current response of the voltage disturbance to obtain the initial transfer function of the sequence impedance model corresponding to each frequency coupling component. The device fully considers the interaction between the grid-connected / connected converters, reveals the frequency coupling law of the converters, and improves the accuracy of the sequence impedance model. Furthermore, the device uses the corrected sequence impedance circuit equation to correct the initial transfer function of the sequence impedance model corresponding to each frequency coupling component to obtain the corrected transfer function of the sequence impedance model of each frequency coupling component, and accurately performs linear modeling on the sequence impedance of the heterogeneous renewable energy grid-connected power system.

[0061] (10) This solution provides a stability analysis method for a heterogeneous renewable energy grid-connected power system, which utilizes the sequence impedance modeling method for the heterogeneous renewable energy grid-connected power system to obtain a sequence impedance model that is accurate and has low computational complexity, thereby providing an effective analysis method for the stability analysis of renewable energy connected to the power grid. Furthermore, the stability analysis of the original power grid network, the grid-connected converter, and the grid-forming converter that are not connected are performed separately, and the grid-forming converter and the grid-forming converter are gradually connected to determine the cause of the instability of the power system. The judgment process has low computational complexity and high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is a flow chart of a sequence impedance modeling method for a heterogeneous renewable energy grid-connected power system provided in Example 1 of the present invention;

[0063] Figure 2aIt is a schematic diagram of the hierarchical analysis process of the heterogeneous renewable energy grid-connected power system provided by Embodiment 1 of the present invention when performing sequence impedance modeling;

[0064] Figure 2b It is an equivalent circuit diagram of the heterogeneous new energy grid-connected power system provided by Embodiment 1 of the present invention when performing sequence impedance modeling;

[0065] Figure 3 It is a system modeling block diagram of a heterogeneous renewable energy grid-connected power system provided by Embodiment 1 of the present invention when performing sequence impedance modeling;

[0066] Figure 4 Schematic diagram of a stability analysis method for a heterogeneous renewable energy grid-connected power system provided in Embodiment 3 of the present invention;

[0067] Figure 5a This is a graph showing the comparison and modeling results of the grid-following converter, grid-forming converter and grid-side equivalent immittance characteristics provided by Example 3 of the present invention;

[0068] Figure 5b is a Nyquist curve diagram of the grid-connected converter provided in Embodiment 3 of the present invention when SCR=1.75 is connected to the grid;

[0069] Figure 5c This is the Nyquist curve of the grid-connected converter provided in Example 3 of the present invention under multiple machine grid connection at different short-circuit ratios. DETAILED DESCRIPTION

[0070] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0071] Example 1

[0072] like Figure 1As shown, this embodiment provides a method for modeling sequence impedance of a heterogeneous renewable energy grid-connected power system, including: S1-S5. S1: Perform two-port equivalent on the grid-type converter and the grid-forming converter in the heterogeneous renewable energy grid-connected power system to obtain a two-port network corresponding to the grid-type converter and the grid-forming converter respectively; the two-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; and a voltage disturbance is added to the AC port and the DC port. S2: Perform sequence impedance modeling on the control loops of the grid-type converter and the grid-forming converter respectively under the current response of the voltage disturbance to obtain a sequence impedance model of the grid-type control loop and a sequence impedance model of the grid-forming control loop. S3: Perform frequency AC / DC coupling analysis on the nonlinear circuits of the grid-type converter and the grid-forming converter respectively under the current response of the voltage disturbance to obtain multiple frequency coupling components; and model the initial transfer function of the sequence impedance model corresponding to each frequency coupling component. S4: Combine the circuit equation of the nonlinear circuit and the control equation of the sequence impedance model of the grid-type control loop and the sequence impedance model of the grid-type control loop, remove the zero-sequence component in the circuit equation, and obtain the corrected sequence impedance circuit equation. S5: Use the corrected sequence impedance circuit equation to correct the initial transfer function of the sequence impedance model corresponding to each frequency coupling component, and obtain the corrected transfer function of the sequence impedance model corresponding to each frequency coupling component.

[0073] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0074] Among them, in step S1, the simplified process of the dual port is:

[0075]

[0076] s p The reference component representing the sequence is multiplied by the reference component matrix on the basis of phase a. The matrix defines the relationship between the sequences. By multiplying the reference component matrix, the complete components of the other three phases can be obtained.

[0077] Specifically, Figure 2a It is a schematic diagram of the hierarchical analysis process of the heterogeneous renewable energy grid-connected power system provided by Embodiment 1 of the present invention when performing sequence impedance modeling; Figure 2b It is an equivalent circuit diagram of the heterogeneous new energy grid-connected power system provided by Embodiment 1 of the present invention when performing sequence impedance modeling; Figure 3 This is a system modeling block diagram of the heterogeneous new energy grid-connected power system provided in Example 1 of the present invention when performing sequence impedance modeling. The sequence impedance modeling of the control loops of the grid-following converter and the grid-connecting converter under the current response of the voltage disturbance includes the current control loop, the voltage control loop, the PLL, and the virtual synchronization loop.

[0078] The modeling process of the current control loop in step S2 is calculated as:

[0079]

[0080] Z c (s) represents the equivalent impedance of the grid type, H c (s) is the gain of the loop, K d represents the feedback gain of the current loop, and L represents the grid-connected inductance of the converter.

[0081] The modeling process of the voltage control loop in step S2 is calculated as:

[0082]

[0083] Z v (s) represents the equivalent impedance of the grid type, H va (s) is the gain of the voltage loop, V dc represents the DC bus voltage gain, and L represents the grid-connected inductance of the converter.

[0084] The modeling process of the PLL phase-locked loop in step S2 is calculated as:

[0085]

[0086] The phase angle in the frequency domain is expressed as H θ (s) is the open-loop gain of the PLL phase-locked PI, T θ (s) is the forward gain of the PLL phase-locked loop, G θ (s) is the closed-loop gain of the PLL phase-locked loop.

[0087] As an optional implementation, the virtual synchronization control in the control loops of the grid-following converter and the grid-forming converter is modeled as follows:

[0088]

[0089] in, is the phase angle in the frequency domain, J is the inertia coefficient of the virtual synchronous control loop, D pis the damping coefficient of the virtual synchronous control loop, is the voltage disturbance applied to the AC port, is the current disturbance after the voltage disturbance added to the AC port, ω0 is the initial rotation angular velocity, ω1 is the fundamental frequency, U1 * 、I1 * are the conjugates of the initial phasors of voltage and current, respectively.

[0090] As a preferred implementation, it should be noted that the frequency coupling of the grid-type and grid-forming converters comes from the nonlinearity of the converter control, but the frequency coupling effect comes from the transmission of the main circuit AC and DC system: dq conversion and PLL, dq conversion will couple out ω p -2ω1 and ω p The +2ω1 component, the PLL control action on the q-axis causes control asymmetry, the DC voltage acts on the d-axis, and the frequency coupling also comes from the modulation action in the main circuit.

[0091] Using the formula Modeling the initial transfer function of the sequence immittance model corresponding to each frequency coupling component;

[0092] Among them, x(t) is the time domain value of the x variable, y(t) is the time domain value of the y variable, is the steady-state value of the x variable at the steady-state operating point, is the superimposed small signal value under small perturbation of x variable, is the steady-state value of the y variable at the steady-state operating point, is the superimposed small signal value under small disturbance of y variable, is the small signal value after the harmonic linearization of Z(t), is the superimposed small signal value under the small disturbance of the y variable, Y l is the steady-state value of the y variable at the steady-state operating point, where l is used to represent the number of components of the y variable itself, X k is the steady-state value of the variable at the steady-state operating point, is the superimposed small signal value under small perturbation of the variable, where k is used to represent the number of components of the x variable itself; ω p is the disturbance frequency, ω1 is the fundamental frequency, is the kth harmonic component of the x variable, is the kth harmonic component of Y.

[0093] As an optional implementation, when a positive sequence voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is:

[0094]

[0095] Among them, Y pp(s) is the positive sequence response self-admittance under positive sequence voltage disturbance, Y pd (s) is the AC-DC coupled admittance of the DC response under positive sequence voltage disturbance, Y pn (s) is the negative sequence response AC transfer admittance under positive sequence voltage disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0096] As an optional implementation, when a negative sequence voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is:

[0097]

[0098] Among them, Y nn (s) is the positive sequence response self-admittance under negative sequence voltage disturbance, Y nd (s) is the AC-DC coupled admittance of the DC response under negative sequence voltage disturbance, Y np (s) is the negative sequence response AC transfer admittance under negative sequence voltage disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0099] As an optional implementation, when a DC voltage disturbance is added to the DC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is:

[0100]

[0101] Among them, Y dd (s) is the DC response self-admittance under DC disturbance, Y dp (s) is the AC-DC coupled admittance of the AC positive sequence response under DC disturbance, Y pn (s) is the AC transfer admittance of the AC negative sequence response under DC disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

[0102] As an optional implementation, the modified transfer function of the grid-following converter is expressed as:

[0103]

[0104] in, is the response current of the AC port, is the voltage disturbance of the AC port, L is the AC inductance, K d is the feedback coefficient of the inner current loop, V dc Represents the DC voltage value, H c (s-jω1) represents the transfer function of the inner current loop, is the fundamental frequency parameter of the modulation signal, The parameter representing the fundamental frequency of the current, represents the conjugate complex number of the fundamental voltage complex number, ω0 represents the base frequency value, G θ (s-jω1) is the closed-loop transfer function of the phase-locked loop, H va (s-jω1) is the transfer function of the AC voltage outer loop, H c (s-jω1) is the transfer function of the inner loop of the AC current, represents the fundamental complex number of admittance, s represents the Laplace factor, and j represents the 90-degree rotation component in the complex frequency domain.

[0105] As an optional implementation, the modified transfer function of the grid-connected converter is expressed as:

[0106]

[0107] Where, L is the AC inductance, K d is the feedback coefficient of the inner current loop, V dc Represents the DC voltage value, H c (s-jω1) represents the transfer function of the inner current loop, is the fundamental frequency parameter of the modulation signal, The parameter representing the fundamental frequency of the current, represents the conjugate complex number of the fundamental current complex number, represents the conjugate complex number of the fundamental voltage complex number, ω0 represents the base frequency value, is the response current of the AC port, H c (s-jω1) is the transfer function of the inner loop of the AC current, is the voltage disturbance of the AC port, and M(s-jω1) represents the transfer function of the virtual synchronous control loop.

[0108] Example 2

[0109] This embodiment provides a sequence immittance modeling device for a heterogeneous renewable energy grid-connected power system, including: a disturbance module, a first modeling module, a second modeling module, a first correction module, and a second correction module.

[0110] The disturbance module is used to perform two-port equivalence on the grid-following converter and the grid-forming converter in the heterogeneous renewable energy grid-connected power system, and obtain the two-port networks corresponding to the grid-following converter and the grid-forming converter respectively; the two-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; and voltage disturbances are added to the AC port and the DC port.

[0111] The first modeling module is used to perform sequence impedance modeling on the control loops of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance, so as to obtain the sequence impedance model of the grid-following control loop and the sequence impedance model of the grid-forming control loop.

[0112] The second modeling module is used to perform frequency AC / DC coupling analysis on the nonlinear circuits of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance to obtain multiple frequency coupling components; and to model the initial transfer function of the sequence immittance model corresponding to each frequency coupling component.

[0113] The first correction module is used to combine the circuit equation of the nonlinear circuit with the control equation of the sequence impedance model of the network-following control loop and the sequence impedance model of the network-forming control loop, remove the zero-sequence component in the circuit equation, and obtain the corrected sequence impedance circuit equation.

[0114] The second correction module is used to correct the initial transfer function of the sequence immittance model corresponding to each frequency coupling component by using the corrected sequence immittance circuit equation to obtain the corrected transfer function of the sequence immittance model corresponding to each frequency coupling component.

[0115] The division of each module in the above-mentioned sequence impedance modeling device for heterogeneous renewable energy grid-connected power system is only for illustration. In other embodiments, the sequence impedance modeling device for heterogeneous renewable energy grid-connected power system can be divided into different modules as needed to complete all or part of the functions of the above-mentioned sequence impedance modeling device for heterogeneous renewable energy grid-connected power system.

[0116] For the specific definition of the sequence impedance modeling device for heterogeneous renewable energy grid-connected power systems, please refer to the definition of the sequence impedance modeling method for heterogeneous renewable energy grid-connected power systems mentioned above, which will not be repeated here. Each module in the above-mentioned sequence impedance modeling device for heterogeneous renewable energy grid-connected power systems can be implemented in whole or in part by software, hardware and a combination thereof. The above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory in the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above modules.

[0117] Example 3

[0118] like Figure 4As shown, this embodiment provides a stability analysis method for a heterogeneous renewable energy grid-connected power system, including: using the sequence impedance modeling method for the heterogeneous renewable energy grid-connected power system provided in Example 1 to construct a modified transfer function of the sequence impedance model of each frequency coupling component; using the modified transfer function to respectively perform impedance modeling on the grid-side system to which the grid-following converter and the grid-forming converter are connected, specifically divided into two methods: if the line connecting the grid side and the source side is long, the impedance analysis of the grid-side system to which each converter is to be connected can be replaced by the impedance of the line; if the line connecting the grid side and the source side is short, it is necessary to partition the grid-side system to be connected, and obtain the impedance of the grid-side system. The equivalent calculated reactance of the converter access port is finally obtained, and the original power grid network without the converter is obtained. The goal of this step is to obtain the grid-side reactance of the heterogeneous new energy grid-connected system to be analyzed, so as to facilitate the subsequent stability analysis; the original power grid network, grid-following converter, and grid-forming converter are separately analyzed for stability. If they are all stable, the grid-forming converter is connected to the original power grid network to determine whether the power system is stable. If it is unstable, it is regarded as the instability of the power system caused by the grid-forming converter; if it is stable, the grid-following converter is connected to the network after the grid-forming converter is connected to the original power grid network to determine whether the power system is stable. If it is unstable, it is regarded as the instability of the power system caused by the grid-forming converter.

[0119] in, Figure 5a This is a graph showing the comparison and modeling results of the grid-following converter, grid-forming converter and grid-side equivalent immittance characteristics provided by Example 3 of the present invention; Figure 5b is a Nyquist curve diagram of the grid-connected converter provided in Embodiment 3 of the present invention when SCR=1.75 is connected to the grid; Figure 5c This is the Nyquist curve of the grid-connected converter under different short-circuit ratios provided by Example 3 of the present invention. The process of stability analysis of the power system is as follows:

[0120] The network voltage-current relationship matrix is ​​classified. When listing the node equations, three types of nodes need to be distinguished. The nodes connected to the converter are numbered as {x1, x2, ..., xn}, and they are collectively represented as x. Assume that the power grid contains m voltage sources at nodes {s1, s2, ..., sm}, and they are represented as s. The voltage source nodes can be further divided into grid-forming converter nodes and generator nodes, which are respectively denoted as s GFM With s Ge The remaining nodes of the power grid are recorded as y. The modified hierarchical sequential network voltage and current equation is formed:

[0121]

[0122] Among them, Y(s) represents the node admittance matrix of each classification node. Vs(s) represents the disturbance voltage of the voltage source node. Vx(s) and Vy(s) represent the voltage response of the non-voltage source node. ix(s) and iy(s) represent the current response of the non-voltage source node. Yxx(s) represents the self-admittance matrix of the x node, and Yyy(s) represents the self-admittance matrix of the and node. Yxy(s) and Yyx(s) represent the mutual admittance matrix between the x and y nodes.

[0123] Furthermore, the network voltage-current relationship matrix is ​​classified, and the three types of nodes need to be distinguished when listing the node equations. Ya(s) is replaced by the converter admittance matrix Yap(s) or Yan(s). The definitions of other admittance matrices involved can be inferred from the standard node voltage equations. Among them, in the hierarchical stability analysis, Ya(s) represents the converter admittance matrix in different hierarchical stability judgment stages. Among them, in the first level of stability judgment, Ya(s) = 0, in the second level of stability judgment, Ya(s) represents the admittance matrix of the access port of the grid-forming converter, and in the third level of stability judgment, Ya(s) represents the admittance matrix of the access port of the grid-following converter.

[0124] Among them, the network voltage-current relationship matrix is ​​used to obtain the hierarchical voltage-current equation expression under the proposed hierarchical sequential stability analysis process:

[0125]

[0126]

[0127] Among them, Y(s) represents the node admittance matrix of each classification node. Vs(s) represents the disturbance voltage of the voltage source node. Vx(s) and Vy(s) represent the voltage response of the non-voltage source node. ix(s) and iy(s) represent the current response of the non-voltage source node. Yxx(s) represents the self-admittance matrix of the x node, and Yyy(s) represents the self-admittance matrix of the and node. Yxy(s) and Yyx(s) represent the mutual admittance matrix between the x and y nodes. Z(s) represents the node impedance matrix of each classification node. Ya(s) represents the admittance matrix of the converter access port node. Ixsum and Iysum represent the sum of the current responses of the x and y nodes.

[0128] Furthermore, the Nyquist stability criterion can be used to analyze the system stability. The core purpose is to use a simplified Nyquist stability criterion so that the stability condition is not to circle or pass through the origin in the complex plane, provided that: 1) the inverter is stable when operating under an ideal voltage source; 2) the grid is stable before the inverter is connected. Therefore, there is no need to check the open-loop RHP poles. This method utilizes the known stability of each part of the system before interconnection, and the loop equation for Nyquist stability can be calculated from the loop equation as follows:

[0129]

[0130] l(s)=det[I+Z xx (s)Y a (s)];

[0131] Here, I is the identity matrix, which indicates the possibility of studying the stability of the system by using a low-dimensional model. The stability of the closed loop depends only on det[I+Zg(s)Ya(s)]. When the first set of grid-connected / constructed converters are connected, the external stability of the grid also guarantees the internal stability of the grid afterwards. This satisfies the condition to re-analyze the above process when the next set of converters are connected. Repeating this, there is no need to model the internal stability separately at any stage. The number of converters and the positions where they are connected to the grid can be completely different. The grid impedance matrix Zg(s) needs to be rebuilt. This allows hierarchical analysis under multi-converter access.

[0132] This embodiment can accurately characterize the stability of the inverter multi-machine grid-connected system and greatly reduce the complexity of stability analysis, realize the hierarchical decoupling of the inverter analysis object, discover the frequency domain instability problems existing in the multi-machine grid-connected system, and improve the stability and adaptability of the inverter multi-machine grid-connected system.

[0133] Example 4

[0134] This embodiment provides a stability analysis device for a heterogeneous renewable energy grid-connected power system, including: a disturbance module, a first modeling module, a second modeling module, a first correction module, a second correction module and a judgment module.

[0135] The disturbance module is used to perform two-port equivalence on the grid-following converter and the grid-forming converter in the heterogeneous renewable energy grid-connected power system, and obtain the two-port networks corresponding to the grid-following converter and the grid-forming converter respectively; the two-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; and voltage disturbances are added to the AC port and the DC port.

[0136] The first modeling module is used to perform sequence impedance modeling on the control loops of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance, so as to obtain the sequence impedance model of the grid-following control loop and the sequence impedance model of the grid-forming control loop.

[0137] The second modeling module is used to perform frequency AC / DC coupling analysis on the nonlinear circuits of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance to obtain multiple frequency coupling components; and to model the initial transfer function of the sequence immittance model corresponding to each frequency coupling component.

[0138] The first correction module is used to combine the circuit equation of the nonlinear circuit with the control equation of the sequence impedance model of the network-following control loop and the sequence impedance model of the network-forming control loop, remove the zero-sequence component in the circuit equation, and obtain the corrected sequence impedance circuit equation.

[0139] The second correction module is used to correct the initial transfer function of the sequence immittance model corresponding to each frequency coupling component by using the corrected sequence immittance circuit equation to obtain the corrected transfer function of the sequence immittance model corresponding to each frequency coupling component.

[0140] The judgment module is used to use the modified transfer function to model the impedance of the grid side to which the grid-following converter and the grid-forming converter are connected, and obtain the original grid network without the converter connected; the original grid network, the grid-following converter, and the grid-forming converter are separately analyzed for stability. If all are stable, the grid-forming converter is connected to the original grid network to determine whether the power system is stable. If it is unstable, it is regarded as the instability of the power system caused by the grid-forming converter; if it is stable, the grid-following converter is connected to the network after the grid-forming converter is connected to the original grid network to determine whether the power system is stable. If it is unstable, it is regarded as the instability of the power system caused by the grid-following converter.

[0141] Example 5

[0142] This embodiment provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, it implements the steps of the sequence impedance modeling method for a heterogeneous new energy grid-connected power system provided in Embodiment 1 or the stability analysis method for a new energy grid-connected power system provided in Embodiment 3.

[0143] Example 6

[0144] This embodiment provides a computer-readable storage medium on which a computer program is stored. When a processor executes the computer program, the steps of the sequence impedance modeling method for a heterogeneous new energy grid-connected power system provided in Example 1 or the stability analysis method for a new energy grid-connected power system provided in Example 3 are implemented.

[0145] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A sequence impedance modeling method for a heterogeneous renewable energy grid-connected power system, characterized in that: include: S1: Perform two-port equivalence on the grid-following converter and the grid-forming converter in the heterogeneous renewable energy grid-connected power system to obtain a two-port network corresponding to the grid-following converter and the grid-forming converter respectively; the two-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; add voltage disturbances to the AC port and the DC port to obtain a current response to the voltage disturbance; S2: performing sequence immittance modeling on the control loops of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance to obtain a sequence immittance model of the grid-following control loop and a sequence immittance model of the grid-forming control loop; S3: performing frequency AC / DC coupling analysis on the nonlinear circuits of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance to obtain multiple frequency coupling components; modeling the initial transfer function of the sequence immittance model corresponding to each frequency coupling component; S4: combining the circuit equation of the nonlinear circuit with the sequence immittance model of the grid-following control loop and the control equation of the sequence immittance model of the grid-forming control loop, removing the zero-sequence component in the circuit equation, and obtaining a corrected sequence immittance circuit equation; S5: using the modified sequence immittance circuit equation to modify the initial transfer function of the sequence immittance model corresponding to each frequency coupling component, to obtain the modified transfer function of the sequence immittance model corresponding to each frequency coupling component.

2. The sequence impedance modeling method for heterogeneous renewable energy grid-connected power systems according to claim 1, characterized in that: The synchronous control modeling in the control loops of the grid-following converter and the grid-building converter are respectively: in, is the phase angle in the frequency domain, J is the inertia coefficient of the virtual synchronous control loop, D p is the damping coefficient of the virtual synchronous control loop, is the voltage disturbance applied to the AC port, is the current disturbance after the voltage disturbance added to the AC port, ω0 is the initial rotation angular velocity, ω1 is the fundamental frequency, U1 * 、I1 * are the conjugates of the initial phasors of voltage and current, respectively.

3. The sequence immittance modeling method for heterogeneous renewable energy grid-connected power systems according to claim 1, characterized in that: Using the formula Modeling the initial transfer function of the sequence immittance model corresponding to each frequency coupling component; Among them, x(t) is the time domain value of the x variable, y(t) is the time domain value of the y variable, is the steady-state value of the x variable at the steady-state operating point, is the superimposed small signal value under small perturbation of x variable, is the steady-state value of the y variable at the steady-state operating point, is the superimposed small signal value under small disturbance of y variable, is the small signal value after the harmonic linearization of Z(t), is the superimposed small signal value under the small disturbance of the y variable, Y l is the steady-state value of the y variable at the steady-state operating point, where l is used to represent the number of components of the y variable itself, X k is the steady-state value of the variable at the steady-state operating point, is the superimposed small signal value under small perturbation of the variable, where k is used to represent the number of components of the x variable itself; ω p is the disturbance frequency, ω1 is the fundamental frequency, X k is the kth harmonic component of the x variable, Y k is the kth harmonic component of Y.

4. The method for sequence immittance modeling of a heterogeneous renewable energy grid-connected power system according to claim 3, characterized in that: When a positive sequence voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is: Among them, Y pp (s) is the positive sequence response self-admittance under positive sequence voltage disturbance, Y pd (s) is the AC-DC coupled admittance of the DC response under positive sequence voltage disturbance, Y pn (s) is the negative sequence response AC transfer admittance under positive sequence voltage disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

5. The sequence impedance modeling method for heterogeneous renewable energy grid-connected power system according to claim 3, characterized in that: When a negative sequence voltage disturbance is added to the AC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is: Among them, Y nn (s) is the positive sequence response self-admittance under negative sequence voltage disturbance, Y nd (s) is the AC-DC coupled admittance of the DC response under negative sequence voltage disturbance, Y np (s) is the negative sequence response AC transfer admittance under negative sequence voltage disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

6. The sequence impedance modeling method for heterogeneous renewable energy grid-connected power system according to claim 3, characterized in that: When a DC voltage disturbance is added to the DC port, the initial transfer function of the sequence immittance model corresponding to each frequency coupling component is: Among them, Y dd (s) is the DC response self-admittance under DC disturbance, Y dp (s) is the AC-DC coupled admittance of the AC positive sequence response under DC disturbance, Y pn (s) is the AC transfer admittance of the AC negative sequence response under DC disturbance; is the response current of the AC port, is the voltage disturbance at the AC port, is the DC current response of the DC port, is the coupling current of the AC port.

7. The sequence immittance modeling method for heterogeneous renewable energy grid-connected power systems according to claim 1, characterized in that: The modified transfer function of the grid-following converter is expressed as: in, is the response current of the AC port, is the voltage disturbance of the AC port, L is the AC inductance, K d is the feedback coefficient of the inner current loop, V dc Represents the DC voltage value, H c (s-jω1) represents the transfer function of the inner current loop, M 1 is the base frequency parameter of the modulation signal, I 1 represents the parameter of the fundamental frequency of the current, represents the conjugate complex number of the fundamental voltage complex number, ω0 represents the base frequency value, G θ (s-jω1) is the closed-loop transfer function of the phase-locked loop, H va (s-jω1) is the transfer function of the AC voltage outer loop, H c (s-jω1) is the transfer function of the inner loop of the AC current, Y 1 represents the fundamental complex number of the admittance, s represents the Laplace factor, and j represents the 90-degree rotation component in the complex frequency domain.

8. The sequence immittance modeling method for heterogeneous renewable energy grid-connected power systems according to claim 7, characterized in that: The modified transfer function of the grid-type converter is expressed as: Where, L is the AC inductance, K d is the feedback coefficient of the inner current loop, V dc Represents the DC voltage value, H c (s-jω1) represents the transfer function of the current inner loop, M1 is the fundamental frequency parameter of the modulation signal, I1 represents the current-fundamental frequency parameter, represents the conjugate complex number of the fundamental current complex number, represents the conjugate complex number of the fundamental voltage complex number, ω0 represents the base frequency value, is the response current of the AC port, H c (s-jω1) is the transfer function of the inner loop of the AC current, is the voltage disturbance of the AC port, and M(s-jω1) represents the transfer function of the virtual synchronous control loop.

9. A sequence impedance modeling device for a heterogeneous renewable energy grid-connected power system, characterized in that: include: A disturbance module is used to perform two-port equivalence on a grid-following converter and a grid-forming converter in a heterogeneous renewable energy grid-connected power system to obtain a two-port network corresponding to the grid-following converter and the grid-forming converter respectively; the two-port network includes: a control loop, a nonlinear circuit, an AC port and a DC port; a voltage disturbance is added to the AC port and the DC port to obtain a current response to the voltage disturbance; A first modeling module is used to perform sequence immittance modeling on the control loops of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance, so as to obtain a sequence immittance model of the grid-following control loop and a sequence immittance model of the grid-forming control loop; The second modeling module is used to perform frequency AC / DC coupling analysis on the nonlinear circuits of the grid-following converter and the grid-forming converter under the current response of the voltage disturbance to obtain multiple frequency coupling components; and to model the initial transfer function of the sequence immittance model corresponding to each frequency coupling component; A first correction module is used to combine the circuit equation of the nonlinear circuit with the control equations of the sequence immittance model of the following-grid control loop and the sequence immittance model of the building-grid control loop, remove the zero-sequence component in the circuit equation, and obtain a corrected sequence immittance circuit equation; The second correction module is used to correct the initial transfer function of the sequence immittance model corresponding to each frequency coupling component by using the corrected sequence immittance circuit equation to obtain the corrected transfer function of the sequence immittance model corresponding to each frequency coupling component.

10. A stability analysis method for a heterogeneous renewable energy grid-connected power system, characterized in that: include: Constructing a modified transfer function of the sequence immittance model of each frequency coupling component by using the sequence immittance modeling method of the heterogeneous renewable energy grid-connected power system as described in any one of claims 1 to 8; Using the modified transfer function, the impedance modeling is performed on the grid side to which the grid-following converter and the grid-forming converter are connected, so as to obtain the original grid network without the converter connected; Perform stability analysis on the original power grid, the grid-following converter, and the grid-forming converter respectively. If all are stable, connect the grid-forming converter to the original power grid to determine whether the power system is stable. If not, it is considered that the power system is unstable due to the grid-forming converter. If it is stable, the grid-following converter is connected to the network after the grid-forming converter is connected to the original power grid network to determine whether the power system is stable. If it is unstable, it is regarded as the power system instability caused by the grid-following converter.

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