Method and system for judging instability mode of grid-connected system based on injection current

Abstract

The invention discloses a grid-connected system instability mode discrimination method and system based on injection current, and belongs to the technical field of power system safety and stability analysis. The method comprises the following steps: constructing a transfer function analysis model of the grid-connected system of the power electronic equipment according to dynamic states and injection currents of a current loop and a phase-locked loop of a converter of the grid-connected system of the power electronic equipment; constructing a power limit model of the power electronic equipment grid-connected system according to the injection current of the power electronic equipment grid-connected system; according to the transfer function analysis model and the power limit model, determining an incidence relation model between stability limits; and judging the instability mode of the power electronic equipment grid-connected system based on the incidence relation model. According to the method, whether the system is unstable or not is judged by constructing the incidence relation model, the method is simple and convenient, and the calculated amount is small.

Description

Technical Field

[0001] The present invention relates to the technical field of power system safety network stability analysis, and more specifically, to a method and system for determining an instability mode of a grid-connected system based on injected current. Background Art

[0002] With the orderly advancement of my country's dual carbon goals and the transformation and upgrading of its energy structure, new energy such as wind power and photovoltaics and flexible direct current transmission systems with power electronic equipment such as voltage source converters (hereinafter referred to as "power electronic equipment") as the core have become key technologies driving the construction of new power systems.

[0003] The large-scale access of power electronic equipment to the power system has induced a series of instability phenomena represented by broadband oscillations. At present, the industry generally ensures the stability of the power electronic equipment access system by setting a minimum short-circuit ratio. In traditional power systems, the static stability of the system can be determined based on the maximum power transmission boundary, and under the condition of constant system power factor, it is only related to the system network structure, that is, the short-circuit ratio of the node. Therefore, the system stability analysis can be obtained by relying on the network node impedance analysis.

[0004] With the large-scale integration of power electronic equipment into the power system, under the control link, the stability of the system is no longer determined solely by the short-circuit ratio of the grid connection point. Stability analysis needs to be determined in combination with the equipment control parameters and control methods. However, the actual system has a variety of operating modes, and various new energy control methods and control parameters are difficult to obtain directly. There is an urgent need for a simplified grid connection capacity calculation index to evaluate the access capability of power electronic equipment. Summary of the invention

[0005] In view of the above problems, the present invention proposes a method for determining the instability mode of a grid-connected system based on injected current, comprising:

[0006] Constructing a transfer function analytical model of the power electronic equipment grid-connected system according to the converter current loop and phase-locked loop dynamics and injected current of the power electronic equipment grid-connected system;

[0007] Constructing a power limit model of the power electronic equipment grid-connected system according to the injected current of the power electronic equipment grid-connected system;

[0008] Determining a correlation model between stability limits according to the transfer function analytical model and the power limit model;

[0009] Based on the association relationship model, the instability mode of the power electronic equipment grid-connected system is judged.

[0010] Optionally, the transfer function analytical model is as follows:

[0011]

[0012] Among them, G0 is the transfer function analytical model, L g is the equivalent filter inductance of the power grid, s is the input frequency, R g is the equivalent resistance of the power grid, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, ξ is the damping ratio of the phase-locked loop control link, ω pll is the phase-locked loop bandwidth, is the grid connection point voltage that changes with the injected current, ω CL is the current loop bandwidth, E is the system equivalent potential, i sq0 For X g is the equivalent filter reactance of the power grid.

[0013] Optional, power limit model, as follows:

[0014]

[0015] Among them, P VSC Inject system power into the converter, is the grid connection point voltage that changes with the injected current, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, i sc is the current node short-circuit current, is the current limit determined by the maximum transmission power of the grid-connected system, E is the equivalent potential of the system, and X g is the equivalent filter reactance of the power grid.

[0016] Optional, stability limits, including:

[0017] The critical current limit is determined by the frequency domain small disturbance stability constraint of the grid equipment and the current limit is determined by the maximum transmission power of the grid-connected system.

[0018] Optional, association relationship model, as follows:

[0019]

[0020] Among them, L is the stability limit discrimination coefficient, G B is the closed-loop transfer function of the phase-locked loop, G C is the current loop transfer function, f is the grid base frequency, s is the input frequency, The current limit determined by the maximum transmission power of the grid-connected system, is the critical current limit determined by the frequency domain small disturbance stability constraint of the network equipment, ω c is the amplitude crossing frequency, j is the imaginary operator;

[0021] Among them, when L<1, the stability of the system is determined by the maximum power transfer limit;

[0022] When L≥1, the system stability is determined by the small disturbance stability limit in the frequency domain.

[0023] On the other hand, the present invention also proposes a grid-connected system instability mode identification system based on injected current, comprising:

[0024] A first calculation unit is used to construct a transfer function analytical model of the power electronic equipment grid-connected system according to the converter current loop and phase-locked loop dynamics and injected current of the power electronic equipment grid-connected system;

[0025] A second calculation unit, configured to construct a power limit model of the power electronic equipment grid-connected system according to an injected current of the power electronic equipment grid-connected system;

[0026] A third calculation unit, configured to determine a correlation model between stability limits according to the transfer function analytical model and the power limit model;

[0027] A determination unit is used to determine the instability mode of the power electronic equipment grid-connected system based on the association relationship model.

[0028] Optionally, the transfer function analytical model is as follows:

[0029]

[0030] Among them, G0 is the transfer function analytical model, L g is the equivalent filter inductance of the power grid, s is the input frequency, R g is the equivalent resistance of the power grid, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, ξ is the damping ratio of the phase-locked loop control link, v pll is the phase-locked loop bandwidth, is the grid connection point voltage that changes with the injected current, ω CL is the current loop bandwidth, E is the system equivalent potential, i sq0 For X g is the equivalent filter reactance of the power grid.

[0031] Optional, power limit model, as follows:

[0032]

[0033] Among them, P VSC Inject system power into the converter, is the grid connection point voltage that changes with the injected current, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, i sc is the current node short-circuit current, is the current limit determined by the maximum transmission power of the grid-connected system, E is the equivalent potential of the system, and X gis the equivalent filter reactance of the power grid.

[0034] Optional, stability limits, including:

[0035] The critical current limit is determined by the frequency domain small disturbance stability constraint of the grid equipment and the current limit is determined by the maximum transmission power of the grid-connected system.

[0036] Optional, association relationship model, as follows:

[0037]

[0038] Among them, L is the stability limit discrimination coefficient, G B is the closed-loop transfer function of the phase-locked loop, G C is the current loop transfer function, f is the grid base frequency, s is the input frequency, The current limit determined by the maximum transmission power of the grid-connected system, is the critical current limit determined by the frequency domain small disturbance stability constraint of the network equipment, ω c is the amplitude crossing frequency, j is the imaginary operator;

[0039] Among them, when L<1, the stability of the system is determined by the maximum power transfer limit;

[0040] When L≥1, the system stability is determined by the small disturbance stability limit in the frequency domain.

[0041] In yet another aspect, the present invention further provides a computing device, comprising: one or more processors;

[0042] a processor for executing one or more programs;

[0043] When the one or more programs are executed by the one or more processors, the above-described method is implemented.

[0044] In yet another aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed, the method described above is implemented.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The present invention proposes a method for identifying the instability mode of a grid-connected system based on injected current, comprising: constructing a transfer function analytical model of the grid-connected system of the power electronic equipment according to the converter current loop and phase-locked loop dynamics and injected current of the grid-connected system of the power electronic equipment; constructing a power limit model of the grid-connected system of the power electronic equipment according to the injected current of the grid-connected system of the power electronic equipment; determining a correlation model between stability limits according to the transfer function analytical model and the power limit model; and identifying the instability mode of the grid-connected system of the power electronic equipment based on the correlation model. The present invention constructs a correlation model to identify whether the system is unstable by using the correlation model, which is simple, convenient and has a small amount of calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a flow chart of the method of the present invention;

[0048] Figure 2 This is a structural diagram of the new energy transmission system via AC according to the method of the present invention;

[0049] Figure 3 Schematic diagram of VSC injection system current under different control parameters of the method of the present invention;

[0050] Figure 4 It is a structural diagram of the system of the present invention. DETAILED DESCRIPTION

[0051] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0052] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0053] Embodiment 1:

[0054] The present invention proposes a method for identifying the instability mode of a grid-connected system based on injected current, such as Figure 1 As shown, including:

[0055] Step 1: constructing a transfer function analytical model of the power electronic equipment grid-connected system according to the converter current loop and phase-locked loop dynamics and injected current of the power electronic equipment grid-connected system;

[0056] Step 2: constructing a power limit model of the power electronic equipment grid-connected system according to the injected current of the power electronic equipment grid-connected system;

[0057] Step 3: Determine a correlation model between stability limits according to the transfer function analytical model and the power limit model;

[0058] Step 4: Based on the association model, the instability mode of the power electronic equipment grid-connected system is determined.

[0059] Among them, the transfer function analytical model is as follows:

[0060]

[0061] Among them, G0 is the transfer function analytical model, L g is the equivalent filter inductance of the power grid, s is the input frequency, R g is the equivalent resistance of the power grid, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, ξ is the damping ratio of the phase-locked loop control link, ω pll is the phase-locked loop bandwidth, is the grid connection point voltage that changes with the injected current, ω CL is the current loop bandwidth, E is the system equivalent potential, i sq0 For X g is the equivalent filter reactance of the power grid.

[0062] Among them, the power limit model is as follows:

[0063]

[0064] Among them, P VSC Inject system power into the converter, is the grid connection point voltage that changes with the injected current, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, i sc is the current node short-circuit current, is the current limit determined by the maximum transmission power of the grid-connected system, E is the equivalent potential of the system, and X g is the equivalent filter reactance of the power grid.

[0065] Among them, the stability limit includes:

[0066] The critical current limit is determined by the frequency domain small disturbance stability constraint of the grid equipment and the current limit is determined by the maximum transmission power of the grid-connected system.

[0067] Among them, the association relationship model is as follows:

[0068]

[0069] Among them, L is the stability limit discrimination coefficient, G B is the closed-loop transfer function of the phase-locked loop, G C is the current loop transfer function, f is the grid base frequency, s is the input frequency, The current limit determined by the maximum transmission power of the grid-connected system, is the critical current limit determined by the frequency domain small disturbance stability constraint of the network equipment, ω c is the amplitude crossing frequency, j is the imaginary operator;

[0070] Among them, when L<1, the stability of the system is determined by the maximum power transfer limit;

[0071] When L≥1, the system stability is determined by the small disturbance stability limit in the frequency domain.

[0072] in, Figure 2 The typical power electronic equipment grid-connected system structure diagram is given, such as Figure 2 As shown,

[0073] and The grid equivalent voltage, grid connection point voltage and converter AC output voltage respectively; Z g , Z eq Represent the equivalent filtering impedance of the power grid and power electronic equipment respectively; R g , R eq Represent the equivalent resistance of the power grid and power electronic equipment respectively; L g , L eq They represent the equivalent filter inductance of the power grid and power electronic equipment respectively, and ω represents the fundamental frequency angular velocity, which is taken as 2π50rad / s here.

[0074] Ignoring the system outer loop control dynamics, only considering the converter current loop and phase-locked loop dynamics, the grid-connected system transfer function analytical model G0 is shown in equation (1).

[0075]

[0076] In the formula, represents the grid connection point voltage that varies with the injected current; E represents the equivalent potential of the system, i sd0 represents the steady-state value of the current injected into the system by the grid-connected VSC; s represents the input frequency; ξ represents the damping ratio of the phase-locked loop control link, which is 0.707; ω pll ,ω CL Respectively represent the phase-locked loop and current loop bandwidth; X g, X eq Represent the equivalent filter reactance of the power grid and power electronic equipment respectively. According to the principle of automatic control, when s = jω c When the system becomes unstable, ω c Represents the amplitude crossover frequency.

[0077] Ignoring the influence of resistance, the power limit of the power electronic equipment grid-connected system can be obtained by equation (2).

[0078]

[0079] Where P VSC Represents the power injected into the system by the converter; represents the converter injection current corresponding to the maximum power transfer limit; i sc Represents the current node short-circuit current.

[0080] According to the amplitude margin definition formula (1), the critical current limit determined by the frequency domain small disturbance stability constraint of the grid-connected equipment is determined According to PI d Curve, formula (2) determines the current limit determined by the maximum transmission power of the grid-connected equipment With short-circuit current i sc As the interface, the correlation between the two types of stability limits can be simplified as shown in formula (3).

[0081]

[0082] Where, L represents the stability limit discrimination coefficient; G B Represents the phase-locked loop closed-loop transfer function, G C represents the current loop transfer function, and f represents the grid fundamental frequency.

[0083] Among them, L≤1 means that the key dominant factor of system instability at this time is the maximum power transmission limit of the node; when L>1, it means that the key dominant factor of system instability at this time is the system control link parameters, and frequency domain small interference stability is the key factor restricting system stability.

[0084] L<1 means that the stability is determined by the maximum power transmission limit at this time, and the access scale of the power electronic equipment can be directly determined according to the short-circuit ratio; L>1 means that the system stability is determined by the small interference stability limit in the frequency domain, and the equipment cannot reach the power transmission limit determined by the system structure under the control dynamic action.

[0085] The invention patent proposes an identification index for the dominant form of power electronic equipment connected to the grid based on the injected current. On the one hand, under the condition that the grid impedance is known, the dominant factor of the stability limit of the equipment connected to the system can be determined based on the maximum current injected into the system by the equipment; on the other hand, under the condition that the grid impedance is unknown, the key restrictive factors of the equipment connected to the system can be determined based on the key control parameters of the equipment.

[0086] like Figure 3 As shown, under the influence of the system grid impedance, the maximum transmission power is P max =0.76pu. Under Case 1, the phase-locked loop bandwidth f pll The frequency domain stability is the key factor that restricts the maximum transmission power of the system. The simulation results show that the maximum transmission power is 0.7064 pu, which is less than the theoretical transmission limit. This is consistent with the results based on the discrimination coefficient. Under Case 2, the phase-locked loop bandwidth f pll The frequency domain stability coincides with the maximum power transmission point at this time. The simulation results show that the maximum power transmission limit is 0.7582pu, which is basically consistent with the theoretical transmission limit. Under Case 2, the phase-locked loop bandwidth f pll The frequency domain stability is no longer the key factor in determining the stability limit of the system. The simulation results show that the system remains unstable as the current increases, which is basically consistent with the theoretical analysis.

[0087] Embodiment 2:

[0088] The present invention also proposes a grid-connected system instability mode identification system 200 based on injected current, such as Figure 4 As shown, including:

[0089] The first calculation unit 201 is used to construct a transfer function analytical model of the power electronic equipment grid-connected system according to the converter current loop and phase-locked loop dynamics and injected current of the power electronic equipment grid-connected system;

[0090] A second calculation unit 202 is used to construct a power limit model of the power electronic equipment grid-connected system according to the injected current of the power electronic equipment grid-connected system;

[0091] A third calculation unit 203 is used to determine a correlation relationship model between stability limits according to the transfer function analytical model and the power limit model;

[0092] The determination unit 204 is used to determine the instability mode of the power electronic equipment grid-connected system based on the association relationship model.

[0093] Among them, the transfer function analytical model is as follows:

[0094]

[0095] Among them, G0 is the transfer function analytical model, L g is the equivalent filter inductance of the power grid, s is the input frequency, R g is the equivalent resistance of the power grid, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, ξ is the damping ratio of the phase-locked loop control link, ω pll is the phase-locked loop bandwidth, is the grid connection point voltage that changes with the injected current, ω CL is the current loop bandwidth, E is the system equivalent potential, i sq0 For X g is the equivalent filter reactance of the power grid.

[0096] Among them, the power limit model is as follows:

[0097]

[0098] Among them, P VSC Inject system power into the converter, is the grid connection point voltage that changes with the injected current, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, i sc is the current node short-circuit current, is the current limit determined by the maximum transmission power of the grid-connected system, E is the equivalent potential of the system, and X g is the equivalent filter reactance of the power grid.

[0099] Among them, the stability limit includes:

[0100] The critical current limit is determined by the frequency domain small disturbance stability constraint of the grid equipment and the current limit is determined by the maximum transmission power of the grid-connected system.

[0101] Among them, the association relationship model is as follows:

[0102]

[0103] Among them, L is the stability limit discrimination coefficient, G B is the closed-loop transfer function of the phase-locked loop, G C is the current loop transfer function, f is the grid base frequency, s is the input frequency, The current limit determined by the maximum transmission power of the grid-connected system, is the critical current limit determined by the frequency domain small disturbance stability constraint of the network equipment, ω c is the amplitude crossing frequency, j is the imaginary operator;

[0104] Among them, when L<1, the stability of the system is determined by the maximum power transfer limit;

[0105] When L≥1, the system stability is determined by the small disturbance stability limit in the frequency domain.

[0106] The present invention constructs an association relationship model to determine whether the system is unstable by using the association relationship model, which is simple and convenient with a small amount of calculation.

[0107] Embodiment 3:

[0108] Based on the same inventive concept, the present invention also provides a computer device, which includes a processor and a memory, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding functions, so as to implement the steps of the method in the above embodiment.

[0109] Embodiment 4:

[0110] Based on the same inventive concept, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium here can include both a built-in storage medium in a computer device and an extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the method in the above embodiment.

[0111] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The schemes in the embodiments of the present invention may be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0112] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0113] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0114] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0115] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0116] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for determining instability mode of a grid-connected system based on injected current, characterized in that: include: Constructing a transfer function analytical model of the power electronic equipment grid-connected system according to the converter current loop and phase-locked loop dynamics and injected current of the power electronic equipment grid-connected system; Constructing a power limit model of the power electronic equipment grid-connected system according to the injected current of the power electronic equipment grid-connected system; Determining a correlation model between stability limits according to the transfer function analytical model and the power limit model; Based on the association relationship model, the instability mode of the power electronic equipment grid-connected system is judged.

2. The method according to claim 1, characterized in that The transfer function analytical model is as follows: Among them, G0 is the transfer function analytical model, L g is the equivalent filter inductance of the power grid, s is the input frequency, R g is the equivalent resistance of the power grid, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, ξ is the damping ratio of the phase-locked loop control link, ω pll is the phase-locked loop bandwidth, is the grid connection point voltage that changes with the injected current, ω CL is the current loop bandwidth, E is the system equivalent potential, i sq0 For X g is the equivalent filter reactance of the power grid.

3. The method according to claim 1, characterized in that The power limit model is as follows: Among them, P VSC Inject system power into the converter, is the grid connection point voltage that changes with the injected current, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, i sc is the current node short-circuit current, is the current limit determined by the maximum transmission power of the grid-connected system, E is the equivalent potential of the system, and X g is the equivalent filter reactance of the power grid.

4. The method according to claim 1, characterized in that: The stability limits include: The critical current limit is determined by the frequency domain small disturbance stability constraint of the grid equipment and the current limit is determined by the maximum transmission power of the grid-connected system.

5. The method according to claim 1, characterized in that The association relationship model is as follows: Among them, L is the stability limit discrimination coefficient, G B is the closed-loop transfer function of the phase-locked loop, G C is the current loop transfer function, f is the grid base frequency, s is the input frequency, The current limit determined by the maximum transmission power of the grid-connected system, is the critical current limit determined by the frequency domain small disturbance stability constraint of the network equipment, ω c is the amplitude crossing frequency, j is the imaginary operator; Among them, when L<1, the stability of the system is determined by the maximum power transfer limit; When L≥1, the system stability is determined by the small disturbance stability limit in the frequency domain.

6. A grid-connected system instability mode identification system based on injected current, characterized in that: include: A first calculation unit is used to construct a transfer function analytical model of the power electronic equipment grid-connected system according to the converter current loop and phase-locked loop dynamics and injected current of the power electronic equipment grid-connected system; A second calculation unit, configured to construct a power limit model of the power electronic equipment grid-connected system according to an injected current of the power electronic equipment grid-connected system; A third calculation unit, configured to determine a correlation model between stability limits according to the transfer function analytical model and the power limit model; A determination unit is used to determine the instability mode of the power electronic equipment grid-connected system based on the association relationship model.

7. The system according to claim 6, characterized in that The transfer function analytical model is as follows: Among them, G0 is the transfer function analytical model, L g is the equivalent filter inductance of the power grid, s is the input frequency, R g is the equivalent resistance of the power grid, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, ξ is the damping ratio of the phase-locked loop control link, ω pll is the phase-locked loop bandwidth, is the grid connection point voltage that changes with the injected current, ω CL is the current loop bandwidth, E is the system equivalent potential, i sq0 For X g is the equivalent filter reactance of the power grid.

8. The system according to claim 6, characterized in that The power limit model is as follows: Among them, P VSC Inject system power into the converter, is the grid connection point voltage that changes with the injected current, i sd0 is the steady-state value of the current injected into the system by the grid-connected VSC, i sc is the current node short-circuit current, is the current limit determined by the maximum transmission power of the grid-connected system, E is the equivalent potential of the system, and X g is the equivalent filter reactance of the power grid.

9. The system according to claim 6, characterized in that The stability limits include: The critical current limit is determined by the frequency domain small disturbance stability constraint of the grid equipment and the current limit is determined by the maximum transmission power of the grid-connected system.

10. The system according to claim 6, characterized in that The association relationship model is as follows: Among them, L is the stability limit discrimination coefficient, G B is the closed-loop transfer function of the phase-locked loop, G C is the current loop transfer function, f is the grid base frequency, s is the input frequency, The current limit determined by the maximum transmission power of the grid-connected system, is the critical current limit determined by the frequency domain small disturbance stability constraint of the network equipment, ω c is the amplitude crossing frequency, j is the imaginary operator; Among them, when L<1, the stability of the system is determined by the maximum power transfer limit; When L≥1, the system stability is determined by the small disturbance stability limit in the frequency domain.

11. A computer device, characterized in that: include: one or more processors; a processor for executing one or more programs; When the one or more programs are executed by the one or more processors, the method according to any one of claims 1 to 5 is implemented.

12. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed, the method according to any one of claims 1 to 5 is implemented.

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