Method, device, equipment and medium for analyzing stability of offshore wind power flexible direct delivery system

Abstract

The invention discloses a stability analysis method, device, equipment and medium for an offshore wind power flexible direct output system, and the method comprises the steps: constructing a matrix expression which corresponds to each subsystem and is used for representing the frequency domain small signal characteristics of the subsystem based on small semaphores corresponding to interconnection ports between adjacent subsystems; further constructing a system matrix used for representing interaction influence characteristics of the subsystems according to the matrix expressions of the subsystems; and then according to the system matrix, calculating to obtain a corresponding Nyquist curve, and then according to the Nyquist curve, judging the stability of the offshore wind power flexible direct delivery system. By implementing the method, the subsystems are associated, so that the influence among the subsystems in the offshore wind power flexible direct delivery system can be fully considered when the stability of the offshore wind power flexible direct delivery system is subsequently analyzed, the dynamic characteristics of the whole system are fully considered, and the stability of the offshore wind power flexible direct delivery system is improved. Therefore, the accuracy of stability analysis of the offshore wind power flexible direct delivery system is improved.

Description

Technical Field

[0001] The present invention relates to the field of power grid optimization, and in particular to a stability analysis method, device, equipment and medium for an offshore wind power flexible direct current transmission system. Background Art

[0002] At present, as my country vigorously promotes the energy revolution, the power generation of renewable resources such as wind and light is booming, and the proportion of installed capacity of new energy is increasing day by day. Thanks to my country's abundant offshore wind energy resources, as well as the advantages of high offshore wind speed and no occupation of land resources, deep-sea wind power generation technology has gradually matured in recent years. The high-voltage direct current transmission technology based on modular multilevel converter (MMC-HVDC) has been widely concerned and applied to the energy transmission of deep-sea wind farms due to its modular design and low harmonic content. However, harmonic oscillation has occurred in many flexible direct current transmission projects in operation, and the oscillation frequency is distributed in a wide frequency band, which seriously affects the safe operation of the power grid. Therefore, the harmonic oscillation problem of flexible direct current interconnection system needs to be paid attention to.

[0003] In the offshore wind farm-flexible direct current grid-connected system, the MMC converter station can be divided into two categories, one is the wind farm side converter station (WSCS) directly connected to the offshore wind farm, and the other is the grid side converter station (GSCS) connected to the onshore power grid. Since the mainstream of wind power is still the grid-connected unit, the WSCS usually adopts AC voltage / frequency (V / f) control to provide stable AC voltage for the offshore wind farm operating on the island to ensure the stable output of electric energy, while the GSCS usually adopts constant DC voltage / reactive power (V / Q) control, and DC voltage-active power droop and constant reactive power (VP / Q) control are also often used in multi-terminal systems. The coordinated operation of WSCS and GSCS realizes the transmission of electric energy in offshore wind farms.

[0004] However, with the increase of installed capacity of new energy, the inertia level of the system has decreased, and the offshore wind farm actively provides inertia support for the system, which has become one of the development directions of offshore wind power technology. The additional frequency control deepens the interactive coupling between the converter stations on both sides, making the dynamic response of the system more complicated. The frequency fluctuation at any end may cause a chain reaction of the entire system, increasing the risk of system instability. Therefore, it is necessary to consider the small disturbance stability analysis method of the double-end converter station dynamics. Summary of the invention

[0005] The present invention provides a method, device, equipment and medium for analyzing the stability of an offshore wind power transmission system via flexible direct current. The method constructs a system matrix based on the parameters of the interconnection ports between the subsystems, thereby solving the system stability through the system matrix, which can fully consider the dynamic characteristics of the entire system and improve the accuracy of the stability analysis of the offshore wind power transmission system via flexible direct current.

[0006] An embodiment of the present invention provides a method for analyzing the stability of an offshore wind power flexible direct current transmission system, comprising:

[0007] Acquire small signal quantities corresponding to interconnection ports between adjacent subsystems; wherein the subsystems include a direct-drive wind farm, a wind farm-side converter station, a DC cable, a grid-side converter station, and an AC grid;

[0008] Constructing a matrix expression corresponding to each subsystem for characterizing the frequency domain small signal characteristics of the subsystem according to the small signal quantity;

[0009] According to the matrix expression corresponding to each subsystem, a system matrix is ​​constructed to characterize the interactive influence characteristics of each subsystem;

[0010] According to the system matrix, a corresponding Nyquist curve is calculated;

[0011] According to the Nyquist curve, the stability of the offshore wind power flexible direct current transmission system is determined.

[0012] Furthermore, the matrix expression corresponding to the direct-drive wind farm and used to characterize the frequency domain small signal characteristics of the subsystem is specifically:

[0013]

[0014]

[0015] In the formula, It is the small signal of d-axis input voltage of direct-drive wind farm; It is the small signal quantity of q-axis input voltage of direct-drive wind farm; is the small signal of the d-axis output current of the direct-drive wind farm; is the q-axis output current small signal of the direct-drive wind farm; The input impedance matrix of the direct-drive wind farm at the offshore grid connection point; It indicates the ratio of the d-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected into the grid connection point of the direct-drive wind farm; It indicates the ratio of the q-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected into the grid connection point of the direct-drive wind farm; It indicates the ratio of the d-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected into the grid connection point of the direct-drive wind farm; It indicates the ratio of the q-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected into the grid connection point of a direct-drive wind farm.

[0016] Furthermore, the matrix expression corresponding to the wind farm side converter station for characterizing the frequency domain small signal characteristics of the subsystem is specifically:

[0017]

[0018]

[0019] In the formula, is the d-axis output voltage small signal quantity on the AC side of the converter station on the wind farm side; is the q-axis output voltage small signal quantity on the AC side of the converter station on the wind farm side; It is the small signal quantity of input voltage on the DC side of the converter station on the wind farm side; It is the small signal quantity of the d-axis input current on the AC side of the converter station on the wind farm side; It is the small signal quantity of the q-axis input current on the AC side of the converter station on the wind farm side; It is the output current small signal quantity of the DC side of the converter station at the wind farm side; It is a hybrid parameter model of the converter station on the wind farm side; When a small d-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small DC current disturbance of a certain frequency is injected at the AC port of the converter station on the wind farm side, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; It is the ratio of the q-axis voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the converter station on the wind farm side; It is the ratio of the DC voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the converter station on the wind farm side.

[0020] Furthermore, the matrix expression corresponding to the grid-side converter station for characterizing the frequency domain small signal characteristics of the subsystem is specifically:

[0021]

[0022]

[0023] In the formula, is the d-axis output voltage small signal quantity of the grid-side converter station; is the q-axis output voltage small signal quantity of the grid-side converter station; is the d-axis output current small signal quantity of the grid-side converter station; It is the q-axis output current small signal quantity of the grid-side converter station; It is the output voltage small signal quantity of the DC side of the grid-side converter station; It is the small signal quantity of input current on the DC side of the grid-side converter station; is the hybrid parameter matrix of the grid-side converter station; When a small d-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected into the AC port of the grid-side converter station, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small DC current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; It is the ratio of the q-axis voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the grid-side converter station; It is the ratio of the DC voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the grid-side converter station.

[0024] Furthermore, the matrix expression corresponding to the AC power grid for characterizing the frequency domain small signal characteristics of the subsystem is specifically:

[0025]

[0026]

[0027] In the formula, is the small signal value of the d-axis input voltage of the AC power grid; is the q-axis input voltage small signal quantity of the AC power grid; is the d-axis input current small signal of the AC power grid; It is the small signal quantity of the q-axis input current of the AC power grid; is the input impedance matrix of the AC grid at the onshore grid connection point; It is the ratio of the d-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the q-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the d-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the q-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected at the grid-connected point.

[0028] Furthermore, the matrix expression corresponding to the AC power grid for characterizing the frequency domain small signal characteristics of the subsystem is specifically:

[0029]

[0030]

[0031] In the formula, is the small signal value of the d-axis input voltage of the AC power grid; is the q-axis input voltage small signal quantity of the AC power grid; is the d-axis input current small signal of the AC power grid; It is the small signal quantity of the q-axis input current of the AC power grid; is the input impedance matrix of the AC grid at the onshore grid connection point; It is the ratio of the d-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the q-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the d-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the q-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected at the grid-connected point.

[0032] Furthermore, the system matrix used to characterize the interaction characteristics of each subsystem is specifically:

[0033]

[0034] In the formula, It is the small signal value of the d-axis input voltage of the offshore direct-drive wind farm, and it is also the small signal value of the d-axis output voltage on the AC side of the converter station on the wind farm side; It is the q-axis input voltage small signal quantity of the offshore direct-drive wind farm, and it is also the q-axis output voltage small signal quantity of the AC side of the converter station on the wind farm side; It is the small signal value of the d-axis output current of the offshore direct-drive wind farm, and it is also the small signal value of the d-axis input current on the AC side of the converter station on the wind farm side; It is the q-axis output current small signal of the offshore direct-drive wind farm, and also the q-axis input current small signal of the AC side of the converter station on the wind farm side; It is the small signal value of the input voltage on the DC side of the converter station on the wind farm side, and it is also the small signal value of the output voltage on the DC cable port on the wind farm side; It is the output current small signal quantity of the DC side of the converter station on the wind farm side, and it is also the input current small signal quantity of the DC cable port on the wind farm side; It is the output voltage small signal quantity of the DC side of the grid-side converter station, and also the input voltage small signal quantity of the DC cable port on the grid side; It is the small signal value of the input current on the DC side of the grid-side converter station, and also the small signal value of the output current on the DC cable port on the wind farm side; It is the small signal value of the d-axis input voltage of the AC power grid and the small signal value of the d-axis output voltage of the converter station on the wind farm side; It is the q-axis input voltage small signal quantity of the AC power grid, and it is also the q-axis output voltage small signal quantity of the converter station on the wind farm side; It is the small signal value of the d-axis input current of the AC power grid, and also the small signal value of the d-axis output current of the power grid side converter station; It is the q-axis input current small signal quantity of the AC power grid, and it is also the q-axis output current small signal quantity of the power grid side converter station; is the hybrid parameter matrix of the grid-side converter station; It is a hybrid parameter model of the converter station on the wind farm side; The input impedance matrix of the direct-drive wind farm at the offshore grid connection point; is the input impedance matrix of the AC grid at the onshore grid connection point; Z DC is the impedance parameter matrix of the DC cable, is the element of the first row and first column of the impedance parameter matrix of the DC cable, is the element in the first row and second column of the impedance parameter matrix of the DC cable, is the element in the second row and first column of the impedance parameter matrix of the DC cable, It is the element in the second row and second column of the impedance parameter matrix of the DC cable.

[0035] An embodiment of the present invention further provides a stability analysis device for an offshore wind power transmission system via flexible direct current, comprising: a small signal quantity acquisition module, a subsystem matrix construction module, a system matrix construction module, a Nyquist curve calculation module, and a stability judgment module;

[0036] The small signal quantity acquisition module is used to acquire the small signal quantity corresponding to the interconnection port between each adjacent subsystem; wherein the subsystem includes a direct-drive wind farm, a wind farm-side converter station, a DC cable, a grid-side converter station and an AC grid;

[0037] The subsystem matrix construction module is used to construct a matrix expression corresponding to each subsystem for characterizing the frequency domain small signal characteristics of the subsystem according to the small signal quantity;

[0038] The system matrix building module is used to build a system matrix for characterizing the interaction characteristics of each subsystem according to the matrix expression corresponding to each subsystem;

[0039] The Nyquist curve calculation module is used to calculate the corresponding Nyquist curve according to the system matrix;

[0040] The stability judgment module is used to judge the stability of the offshore wind power flexible direct current transmission system according to the Nyquist curve.

[0041] The present application also provides a terminal device, including:

[0042] one or more processors;

[0043] A memory, coupled to the processor, for storing one or more programs;

[0044] When the one or more programs are executed by the one or more processors, the one or more processors implement the offshore wind power flexible direct current transmission system stability analysis method as described in the above-mentioned embodiment of the invention.

[0045] The present application also provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the method for analyzing the stability of an offshore wind power system via flexible direct current transmission as described in the above-mentioned embodiment of the invention is implemented.

[0046] The following beneficial effects are achieved by implementing the present invention:

[0047] The present invention provides a stability analysis method for an offshore wind power transmission system via flexible direct current. The method divides the offshore wind power transmission system via flexible direct current into several subsystems, and obtains the small signal quantity corresponding to the interconnection port between each subsystem, thereby constructing a matrix expression for characterizing the frequency domain small signal characteristics of the subsystem; thus, by dividing the subsystems, the complexity of the offshore wind power transmission system via flexible direct current can be decomposed into smaller and easier to handle parts, reducing the complexity of subsequent analysis; then, through the matrix expression of each subsystem, a system matrix for characterizing the interactive influence characteristics of each subsystem is constructed, thereby, the relationship between the subsystems is associated, and the wind farm side converter station and the grid side converter station are analyzed as subsystems respectively, so that the interaction between the converter stations on both sides can be better understood, so that when the stability analysis of the offshore wind power transmission system via flexible direct current is performed subsequently, the influence between the subsystems in the offshore wind power transmission system via flexible direct current can be fully considered, and the constructed system matrix can fully consider the dynamic characteristics of the whole system, thereby improving the accuracy of the stability analysis of the offshore wind power transmission system via flexible direct current, and providing a basis for the impedance reshaping of the interconnected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the implementation manner will be briefly introduced below. Obviously, the drawings described below are only some implementation manners of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0049] Figure 1 It is a flowchart of a method for analyzing the stability of an offshore wind power system via flexible direct current transmission provided by a certain embodiment of the present application;

[0050] Figure 2 This is a control block diagram of an offshore wind power transmission system via MMC-HVDC provided in a certain embodiment of the present application;

[0051] Figure 3 This is a schematic diagram of the subsystem division of an offshore wind power flexible direct current transmission system provided in a certain embodiment of the present application;

[0052] Figure 4 It is a waveform diagram of an electromagnetic transient time-domain simulation flexible direct current converter station provided in a certain embodiment of the present application;

[0053] Figure 5 It is a Nyquist curve of the closed-loop transfer function determinant of an offshore wind power-flexible direct current system provided by a certain embodiment of the present application;

[0054] Figure 6 is the amplitude-frequency characteristic and imaginary frequency characteristic of the closed-loop transfer function provided by a certain embodiment of the present application;

[0055] Figure 7 It is a structural schematic diagram of a stability analysis device for an offshore wind power flexible direct current transmission system provided in a certain embodiment of the present application;

[0056] Figure 8 It is a structural diagram of a terminal device provided in a certain embodiment of the present application. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0059] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0060] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0061] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0062] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0063] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0064] See also Figure 1 , is a flow chart of a method for analyzing the stability of an offshore wind power system via flexible direct current transmission provided by an embodiment of the present invention, comprising:

[0065] S1. Obtaining small signal quantities corresponding to interconnection ports between adjacent subsystems; wherein the subsystems include a direct-drive wind farm, a wind farm-side converter station, a DC cable, a grid-side converter station, and an AC grid;

[0066] Specifically, Figure 2The control structure diagram of offshore wind power connected to the grid via MMC-HVDC is shown in Figure 1. The permanent magnet synchronous generator (PMSG) is connected to the machine side converter (MSC) and GSC, and then connected to the WFVSC through an AC submarine cable. The WFVSC converts AC power into DC power and transmits the power to the GSVSC through a submarine cable and then connects it to the grid. There is an electric load at the point of common coupling (PCC) on land. The AC side of the GSVSC is connected to the synchronous generator (SG) group to jointly maintain the load power consumption. In the figure, θ is the synchronous phase output by the phase-locked loop / virtual synchronization link, and U abc,WF is the voltage at the interconnected system PCC, I abc,WF is the current at the interconnected system PCC, U dc is the DC side voltage of MMC-HVDC, U abc,GS is the voltage at the PCC on the AC side of GSVSC, I abc,GS is the current at the PCC on the AC side of GSVSC, u dc,ref is the DC voltage reference value;

[0067] Specifically, in order to facilitate subsequent stability analysis, this application divides the system into five subsystems. Among them, the actual wind farm may contain wind turbines from multiple manufacturers, and the operating conditions of different wind turbines are also different. Therefore, the wind turbines from different manufacturers and regions can be equivalently aggregated to form a direct-drive wind farm subsystem.

[0068] S2. constructing a matrix expression corresponding to each subsystem for characterizing the frequency domain small signal characteristics of the subsystem according to the small signal quantity;

[0069] Indicatively, see Figure 3 , the offshore wind power transmission system is divided into five subsystems and four interconnection ports. Then, each subsystem is modeled to obtain the matrix expression describing the frequency domain small signal characteristics of each device;

[0070] In a preferred embodiment, the matrix expression corresponding to the direct-drive wind farm and used to characterize the frequency domain small signal characteristics of the subsystem is specifically:

[0071]

[0072]

[0073] In the formula, It is the small signal of d-axis input voltage of direct-drive wind farm; It is the small signal quantity of q-axis input voltage of direct-drive wind farm; is the small signal of the d-axis output current of the direct-drive wind farm; is the q-axis output current small signal of the direct-drive wind farm; The input impedance matrix of the direct-drive wind farm at the offshore grid connection point; It indicates the ratio of the d-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected into the grid connection point of the direct-drive wind farm; It indicates the ratio of the q-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected into the grid connection point of the direct-drive wind farm; It indicates the ratio of the d-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected into the grid connection point of the direct-drive wind farm; It indicates the ratio of the q-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected into the grid connection point of a direct-drive wind farm.

[0074] In a preferred embodiment, the matrix expression corresponding to the wind farm side converter station and used to characterize the frequency domain small signal characteristics of the subsystem is specifically:

[0075]

[0076]

[0077] In the formula, is the d-axis output voltage small signal quantity on the AC side of the converter station on the wind farm side; is the q-axis output voltage small signal quantity on the AC side of the converter station on the wind farm side; It is the small signal quantity of input voltage on the DC side of the converter station on the wind farm side; It is the small signal quantity of the d-axis input current on the AC side of the converter station on the wind farm side; It is the small signal quantity of the q-axis input current on the AC side of the converter station on the wind farm side; It is the output current small signal quantity of the DC side of the converter station at the wind farm side; It is a hybrid parameter model of the converter station on the wind farm side; When a small d-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small DC current disturbance of a certain frequency is injected at the AC port of the converter station on the wind farm side, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; It is the ratio of the q-axis voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the converter station on the wind farm side; It is the ratio of the DC voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the converter station on the wind farm side.

[0078] In a preferred embodiment, the matrix expression corresponding to the grid-side converter station and used to characterize the frequency domain small signal characteristics of the subsystem is specifically:

[0079]

[0080]

[0081] In the formula, is the d-axis output voltage small signal quantity of the grid-side converter station; is the q-axis output voltage small signal quantity of the grid-side converter station; is the d-axis output current small signal quantity of the grid-side converter station; It is the q-axis output current small signal quantity of the grid-side converter station; It is the output voltage small signal quantity of the DC side of the grid-side converter station; It is the small signal quantity of input current on the DC side of the grid-side converter station; is the hybrid parameter matrix of the grid-side converter station; When a small d-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small DC current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; It is the ratio of the q-axis voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the grid-side converter station; It is the ratio of the DC voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the grid-side converter station.

[0082] In a preferred embodiment, the matrix expression corresponding to the AC power grid and used to characterize the frequency domain small signal characteristics of the subsystem is specifically:

[0083]

[0084]

[0085] In the formula, is the small signal value of the d-axis input voltage of the AC power grid; is the q-axis input voltage small signal quantity of the AC power grid; is the d-axis input current small signal of the AC power grid; It is the small signal quantity of the q-axis input current of the AC power grid; is the input impedance matrix of the AC grid at the onshore grid connection point; It is the ratio of the d-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the q-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the d-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the q-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected at the grid-connected point.

[0086] In a preferred embodiment, the matrix expression corresponding to the DC cable and used to characterize the frequency domain small signal characteristics of the subsystem is specifically:

[0087]

[0088]

[0089] In the formula, is the output voltage small signal quantity of the DC cable port on the wind farm side; It is the small signal value of the input voltage of the DC cable port on the grid side; is the small signal value of the input current of the DC cable port on the wind farm side; is the output current small signal quantity of the DC cable port at the wind farm side; Z DC is the impedance parameter matrix of the DC cable; When a small disturbance of DC current of a certain frequency is injected into the DC port on the wind farm side, the ratio of the voltage disturbance responded by the DC port on the wind farm side to the injected current disturbance; When a small disturbance of DC current of a certain frequency is injected into the DC port on the wind farm side, the ratio of the voltage disturbance responded by the DC port on the grid side to the injected current disturbance; It is the ratio of the voltage disturbance responded by the DC port on the wind farm side to the injected current disturbance when a small DC current disturbance of a certain frequency is injected into the DC port on the grid side; It is the ratio of the voltage disturbance responded by the DC port on the grid side to the injected current disturbance when a small DC current disturbance of a certain frequency is injected into the DC port on the grid side.

[0090] S3. Based on the matrix expression corresponding to each subsystem, a system matrix is ​​constructed to characterize the interaction characteristics of each subsystem;

[0091] Indicatively, according to the matrix expressions of each subsystem constructed in step S3 and the input-output coupling relationship of the small signal quantity between each subsystem, a system matrix of the offshore wind power flexible direct current grid-connected system is generated;

[0092] Specifically, construct a 12-dimensional matrix H sys , where H(m1:m2,n1:n2) represents a block matrix consisting of the elements of the intersection of the matrix from row m1 to row m2 and from column n1 to column n2;

[0093] First, the closed-loop transfer function matrix H sys To split into blocks:

[0094] Set H(1:3,1:3), H(1:3,7:12), H(4:5,3:12), H(6:6,1:2), H(6:6,4:8), H(7:11,1:6), H(6:9,10:12), H(10:11,9:12), H(12:12,1:2), H(12:12,4:8), H(12:12,10:12) to zero matrix;

[0095] Set H(1:3,4:6) as the hybrid parameter model of the wind farm side converter station

[0096] Set H(7:9,7:9) as the hybrid parameter model of the grid-side converter station

[0097] Set H(4:5,1:2) as the input impedance of the direct-drive wind farm at the offshore grid connection point

[0098] Set H(10:11,7:8) as the input impedance of the AC grid at the onshore connection point

[0099] Set H(6:6,3:3) as the impedance parameter matrix Z of the submarine DC cable DC The first row and first column of the element, H(6:6,9:9) is set as the impedance parameter matrix Z of the submarine DC cable DC The first row and second column of the element, H(12:12,3:3) is set as the impedance parameter matrix Z of the submarine DC cable DC The element of the second row and first column of , sets H(12:12,9:9) as the impedance parameter matrix Z of the submarine DC cable DC The element in the second row and second column of ;

[0100] At this point, the construction of the system matrix is ​​completed;

[0101] In a preferred embodiment, the system matrix used to characterize the interaction characteristics of each subsystem is specifically:

[0102]

[0103] In the formula, It is the small signal value of the d-axis input voltage of the offshore direct-drive wind farm, and it is also the small signal value of the d-axis output voltage on the AC side of the converter station on the wind farm side; It is the q-axis input voltage small signal quantity of the offshore direct-drive wind farm, and it is also the q-axis output voltage small signal quantity of the AC side of the converter station on the wind farm side; It is the small signal value of the d-axis output current of the offshore direct-drive wind farm, and it is also the small signal value of the d-axis input current on the AC side of the converter station on the wind farm side; It is the q-axis output current small signal of the offshore direct-drive wind farm, and also the q-axis input current small signal of the AC side of the converter station on the wind farm side; It is the small signal value of the input voltage on the DC side of the converter station on the wind farm side, and it is also the small signal value of the output voltage on the DC cable port on the wind farm side; It is the output current small signal quantity of the DC side of the converter station on the wind farm side, and it is also the input current small signal quantity of the DC cable port on the wind farm side; It is the output voltage small signal quantity of the DC side of the grid-side converter station, and also the input voltage small signal quantity of the DC cable port on the grid side; It is the small signal value of the input current on the DC side of the grid-side converter station, and also the small signal value of the output current on the DC cable port on the wind farm side; It is the small signal value of the d-axis input voltage of the AC power grid and the small signal value of the d-axis output voltage of the converter station on the wind farm side; It is the q-axis input voltage small signal quantity of the AC power grid, and it is also the q-axis output voltage small signal quantity of the converter station on the wind farm side; It is the small signal value of the d-axis input current of the AC power grid, and also the small signal value of the d-axis output current of the power grid side converter station; It is the q-axis input current small signal quantity of the AC power grid, and it is also the q-axis output current small signal quantity of the power grid side converter station; is the hybrid parameter matrix of the grid-side converter station; It is a hybrid parameter model of the converter station on the wind farm side; The input impedance matrix of the direct-drive wind farm at the offshore grid connection point; is the input impedance matrix of the AC grid at the onshore grid connection point; Z DC is the impedance parameter matrix of the DC cable, is the element of the first row and first column of the impedance parameter matrix of the DC cable, is the element in the first row and second column of the impedance parameter matrix of the DC cable, is the element in the second row and first column of the impedance parameter matrix of the DC cable, It is the element in the second row and second column of the impedance parameter matrix of the DC cable.

[0104] S4. Calculate and obtain a corresponding Nyquist curve according to the system matrix;

[0105] Specifically, the system matrix H constructed according to step S3 is sys , determine the closed-loop transfer function matrix G of the system cl =IH sys , where I is sys Identity matrices of the same order;

[0106] Then, by judging the closed-loop transfer function matrix G cl The zero-point distribution of can be used to analyze the stability of the system;

[0107] Specifically, the calculation and drawing of the Nyquist curve can be achieved through computing software. Since the method for drawing the Nyquist curve is already mature, the specific drawing process will not be described in detail in this application.

[0108] S5. According to the Nyquist curve, determine the stability of the offshore wind power flexible direct current transmission system;

[0109] Specifically, according to the generalized Nyquist theory, the stability of the system can be equivalent to the closed-loop transfer function determinant G of the system when s moves around an infinite semicircle on the right complex plane: cl The Nyquist curve of (s)| does not go around the point (0,0);

[0110] Therefore, after the corresponding Nyquist curve is drawn in step S4, when it is determined that the Nyquist curve does not bypass the point (0,0), it is determined that the current offshore wind power transmission system via flexible direct current is stable.

[0111] To better illustrate this application, the Qingzhou 5 / 7 offshore wind power-flexible direct current project is used as an example. At the beginning, the system runs at a transmission power of 0.85pu. At this time, the system can run stably. When the wind farm output power is gradually increased to 1.1pu, the system appears as follows: Figure 4 The harmonic oscillation problem shown has a harmonic frequency of about 83Hz. Figure 4 The transmission power waveforms of the four ports are shown. It can be seen that the harmonic power is more obvious on the wind farm side, but is reduced on the DC port, and the harmonic power on the grid side is relatively small.

[0112] exist Figure 5 In the figure, the Nyquist curve has four negative crossing intersections and two positive crossing intersections with the negative real axis, which means that the system is unstable.

[0113] Figure 6 The Nyquist curve of the determinant of the closed-loop transfer function of the system in this case is plotted, showing the amplitude-frequency characteristics and imaginary frequency characteristics of the closed-loop transfer function of the system in this case. It can be seen that its imaginary frequency characteristic crosses the zero line at 83.8Hz, and its amplitude-frequency characteristic is close to zero at this point. Therefore, it can be estimated that the frequency of the unstable oscillation mode is 83.8Hz, and the oscillation mode S is accurately calculated. m =0.5339+j527.0342, and its frequency is 83.8801Hz, which is slightly different from the estimated value.

[0114] because Figure 4 Simulation results and Figure 5-Figure 6 The grid-connected stability analysis results are consistent with the Figure 5as well as Figure 6 The correctness of the grid-connected stability analysis also shows that the offshore wind power flexible direct current transmission system stability analysis method proposed in the present invention can effectively and accurately analyze the system small disturbance stability.

[0115] See also Figure 7 , is a stability analysis device for an offshore wind power system via flexible direct current transmission provided by a certain embodiment of the present application, comprising: a small signal quantity acquisition module, a subsystem matrix construction module, a system matrix construction module, a Nyquist curve calculation module and a stability judgment module;

[0116] The small signal quantity acquisition module is used to acquire the small signal quantity corresponding to the interconnection port between each adjacent subsystem; wherein the subsystem includes a direct-drive wind farm, a wind farm-side converter station, a DC cable, a grid-side converter station and an AC grid;

[0117] The subsystem matrix construction module is used to construct a matrix expression corresponding to each subsystem for characterizing the frequency domain small signal characteristics of the subsystem according to the small signal quantity;

[0118] The system matrix building module is used to build a system matrix for characterizing the interaction characteristics of each subsystem according to the matrix expression corresponding to each subsystem;

[0119] The Nyquist curve calculation module is used to calculate the corresponding Nyquist curve according to the system matrix;

[0120] The stability judgment module is used to judge the stability of the offshore wind power flexible direct current transmission system according to the Nyquist curve.

[0121] See also Figure 8 , a certain embodiment of the present application further provides a terminal device, including:

[0122] one or more processors;

[0123] A memory, coupled to the processor, for storing one or more programs;

[0124] When the one or more programs are executed by the one or more processors, the one or more processors implement the offshore wind power flexible direct current transmission system stability analysis method as described above.

[0125] The processor is used to control the overall operation of the terminal device to complete all or part of the steps of the above-mentioned offshore wind power flexible direct current transmission system stability analysis method. The memory is used to store various types of data to support the operation of the terminal device, and these data may include, for example, instructions for any application or method used to operate on the terminal device, and application-related data. The memory can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (Static Random Access Memory, referred to as SRAM), electrically erasable programmable read-only memory (Electrically Erasable Programmable Read-Only Memory, referred to as EEPROM), erasable programmable read-only memory (Erasable Programmable Read-Only Memory, referred to as EPROM), programmable read-only memory (Programmable Read-Only Memory, referred to as PROM), read-only memory (Read-Only Memory, referred to as ROM), magnetic memory, flash memory, disk or optical disk.

[0126] In an exemplary embodiment, the terminal device can be implemented by one or more application specific integrated circuits (ASIC), digital signal processors (DSP), digital signal processing devices (DSPD), programmable logic devices (PLD), field programmable gate arrays (FPGA), controllers, microcontrollers, microprocessors or other electronic components to execute the offshore wind power flexible direct current transmission system stability analysis method as described in any of the above embodiments, and achieve the same technical effect as the above method.

[0127] In another exemplary embodiment, a computer-readable storage medium including a computer program is also provided, and when the computer program is executed by a processor, the steps of the offshore wind power flexible direct current transmission system stability analysis method as described in any of the above embodiments are implemented. For example, the computer-readable storage medium can be the above-mentioned memory including the computer program, and the above-mentioned computer program can be executed by the processor of the terminal device to complete the offshore wind power flexible direct current transmission system stability analysis method as described in any of the above embodiments, and achieve the technical effect consistent with the above method.

[0128] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for analyzing the stability of an offshore wind power transmission system via flexible direct current transmission, characterized in that: include: Acquire small signal quantities corresponding to interconnection ports between adjacent subsystems; wherein the subsystems include a direct-drive wind farm, a wind farm-side converter station, a DC cable, a grid-side converter station, and an AC grid; Constructing a matrix expression corresponding to each subsystem according to the small signal quantity and used to characterize the frequency domain small signal characteristics of the subsystem; According to the matrix expression corresponding to each subsystem, a system matrix is ​​constructed to characterize the interactive influence characteristics of each subsystem; According to the system matrix, a corresponding Nyquist curve is calculated; According to the Nyquist curve, the stability of the offshore wind power flexible direct current transmission system is determined.

2. The offshore wind power flexible direct current transmission system stability analysis method according to claim 1, characterized in that: The matrix expression corresponding to the direct-drive wind farm and used to characterize the frequency domain small signal characteristics of the subsystem is specifically: In the formula, It is the small signal of d-axis input voltage of direct-drive wind farm; It is the small signal quantity of q-axis input voltage of direct-drive wind farm; is the small signal of the d-axis output current of the direct-drive wind farm; is the q-axis output current small signal of the direct-drive wind farm; The input impedance matrix of the direct-drive wind farm at the offshore grid connection point; It indicates the ratio of the d-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected into the grid connection point of the direct-drive wind farm; It indicates the ratio of the q-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected into the grid connection point of the direct-drive wind farm; It indicates the ratio of the d-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected into the grid connection point of the direct-drive wind farm; It indicates the ratio of the q-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected into the grid connection point of a direct-drive wind farm.

3. The offshore wind power flexible direct current transmission system stability analysis method according to claim 1, characterized in that: The matrix expression corresponding to the wind farm side converter station and used to characterize the frequency domain small signal characteristics of the subsystem is specifically: In the formula, is the d-axis output voltage small signal quantity on the AC side of the converter station on the wind farm side; is the q-axis output voltage small signal quantity on the AC side of the converter station on the wind farm side; It is the small signal quantity of input voltage on the DC side of the converter station on the wind farm side; It is the small signal quantity of the d-axis input current on the AC side of the converter station on the wind farm side; It is the small signal quantity of the q-axis input current on the AC side of the converter station on the wind farm side; It is the output current small signal quantity of the DC side of the converter station at the wind farm side; It is a hybrid parameter model of the converter station on the wind farm side; When a small d-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected into the AC port of the converter station on the wind farm side, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small DC current disturbance of a certain frequency is injected at the AC port of the converter station on the wind farm side, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; It is the ratio of the q-axis voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the converter station on the wind farm side; It is the ratio of the DC voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the converter station on the wind farm side.

4. The offshore wind power flexible direct current transmission system stability analysis method according to claim 1, characterized in that: The matrix expression corresponding to the grid-side converter station and used to characterize the frequency domain small signal characteristics of the subsystem is specifically: In the formula, is the d-axis output voltage small signal quantity of the grid-side converter station; is the q-axis output voltage small signal quantity of the grid-side converter station; is the d-axis output current small signal quantity of the grid-side converter station; It is the q-axis output current small signal quantity of the grid-side converter station; It is the output voltage small signal quantity of the DC side of the grid-side converter station; It is the small signal quantity of input current on the DC side of the grid-side converter station; is the hybrid parameter matrix of the grid-side converter station; When a small d-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small d-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the q-axis voltage signal of the frequency to the injected current disturbance is obtained; When a small q-axis current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the DC voltage signal of the frequency to the injected current disturbance is obtained; When a small DC current disturbance of a certain frequency is injected at the AC port of the grid-side converter station, the ratio of the d-axis voltage signal of the frequency to the injected current disturbance is obtained; It is the ratio of the q-axis voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the grid-side converter station; It is the ratio of the DC voltage signal of a certain frequency to the injected current disturbance when a small DC current disturbance of a certain frequency is injected at the AC port of the grid-side converter station.

5. The offshore wind power flexible direct current transmission system stability analysis method according to claim 1, characterized in that: The matrix expression corresponding to the AC power grid and used to characterize the frequency domain small signal characteristics of the subsystem is specifically: In the formula, is the small signal value of the d-axis input voltage of the AC power grid; is the q-axis input voltage small signal quantity of the AC power grid; is the d-axis input current small signal of the AC power grid; It is the small signal quantity of the q-axis input current of the AC power grid; is the input impedance matrix of the AC grid at the onshore grid connection point; It is the ratio of the d-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the q-axis voltage disturbance to the injected current disturbance when a small d-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the d-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected at the grid-connected point. It is the ratio of the q-axis voltage disturbance to the injected current disturbance when a small q-axis current disturbance of a certain frequency is injected at the grid-connected point.

6. The offshore wind power flexible direct current transmission system stability analysis method according to claim 1, characterized in that: The matrix expression corresponding to the DC cable and used to characterize the frequency domain small signal characteristics of the subsystem is specifically: In the formula, is the output voltage small signal quantity of the DC cable port on the wind farm side; It is the small signal value of the input voltage of the DC cable port on the grid side; is the small signal value of the input current of the DC cable port on the wind farm side; is the output current small signal quantity of the DC cable port at the wind farm side; Z DC is the impedance parameter matrix of the DC cable; When a small disturbance of DC current of a certain frequency is injected into the DC port on the wind farm side, the ratio of the voltage disturbance responded by the DC port on the wind farm side to the injected current disturbance; When a small disturbance of DC current of a certain frequency is injected into the DC port on the wind farm side, the ratio of the voltage disturbance responded by the DC port on the grid side to the injected current disturbance; It is the ratio of the voltage disturbance responded by the DC port on the wind farm side to the injected current disturbance when a small DC current disturbance of a certain frequency is injected into the DC port on the grid side; It is the ratio of the voltage disturbance responded by the DC port on the grid side to the injected current disturbance when a small DC current disturbance of a certain frequency is injected into the DC port on the grid side.

7. The offshore wind power flexible direct current transmission system stability analysis method according to claim 1, characterized in that: The system matrix used to characterize the interaction characteristics of each subsystem is specifically: In the formula, It is the small signal value of the d-axis input voltage of the offshore direct-drive wind farm, and it is also the small signal value of the d-axis output voltage on the AC side of the converter station on the wind farm side; It is the q-axis input voltage small signal quantity of the offshore direct-drive wind farm, and it is also the q-axis output voltage small signal quantity of the AC side of the converter station on the wind farm side; It is the small signal value of the d-axis output current of the offshore direct-drive wind farm, and it is also the small signal value of the d-axis input current on the AC side of the converter station on the wind farm side; It is the q-axis output current small signal of the offshore direct-drive wind farm, and also the q-axis input current small signal of the AC side of the converter station on the wind farm side; It is the small signal value of the input voltage on the DC side of the converter station on the wind farm side, and it is also the small signal value of the output voltage on the DC cable port on the wind farm side; It is the output current small signal quantity of the DC side of the converter station on the wind farm side, and it is also the input current small signal quantity of the DC cable port on the wind farm side; It is the output voltage small signal quantity of the DC side of the grid-side converter station, and also the input voltage small signal quantity of the DC cable port on the grid side; It is the small signal value of the input current on the DC side of the grid-side converter station, and also the small signal value of the output current on the DC cable port on the wind farm side; It is the small signal value of the d-axis input voltage of the AC power grid and the small signal value of the d-axis output voltage of the converter station on the wind farm side; It is the q-axis input voltage small signal quantity of the AC power grid, and it is also the q-axis output voltage small signal quantity of the converter station on the wind farm side; It is the small signal value of the d-axis input current of the AC power grid, and also the small signal value of the d-axis output current of the power grid side converter station; It is the q-axis input current small signal quantity of the AC power grid, and it is also the q-axis output current small signal quantity of the power grid side converter station; is the hybrid parameter matrix of the grid-side converter station; It is a hybrid parameter model of the converter station on the wind farm side; The input impedance matrix of the direct-drive wind farm at the offshore grid connection point; is the input impedance matrix of the AC grid at the onshore grid connection point; Z DC is the impedance parameter matrix of the DC cable, is the element of the first row and first column of the impedance parameter matrix of the DC cable, is the element in the first row and second column of the impedance parameter matrix of the DC cable, is the element in the second row and first column of the impedance parameter matrix of the DC cable, It is the element in the second row and second column of the impedance parameter matrix of the DC cable.

8. A stability analysis device for an offshore wind power transmission system via flexible direct current, characterized in that: include: Small signal acquisition module, subsystem matrix construction module, system matrix construction module, Nyquist curve calculation module and stability judgment module; The small signal quantity acquisition module is used to acquire the small signal quantity corresponding to the interconnection port between each adjacent subsystem; wherein the subsystem includes a direct-drive wind farm, a wind farm-side converter station, a DC cable, a grid-side converter station and an AC grid; The subsystem matrix construction module is used to construct a matrix expression corresponding to each subsystem for characterizing the frequency domain small signal characteristics of the subsystem according to the small signal quantity; The system matrix building module is used to build a system matrix for characterizing the interaction characteristics of each subsystem according to the matrix expression corresponding to each subsystem; The Nyquist curve calculation module is used to calculate the corresponding Nyquist curve according to the system matrix; The stability judgment module is used to judge the stability of the offshore wind power flexible direct current transmission system according to the Nyquist curve.

9. A device, characterized in that: include: one or more processors; A memory, coupled to the processor, for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the offshore wind power flexible direct current transmission system stability analysis method as described in any one of claims 1-7.

10. A medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for analyzing the stability of an offshore wind power flexible direct current transmission system as described in any one of claims 1 to 7 is implemented.

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