Method, system and device for analyzing resonance stability of offshore wind power grid-connected system and storage medium

Abstract

The application discloses a kind of offshore wind power grid-connected system resonance stability analysis method, system, equipment and storage medium.The method of the present application comprises: establishing the s-domain impedance model of each electrical equipment of offshore wind power grid-connected system;According to the topology structure of target offshore wind farm, the s-domain equivalent circuit is constructed, and then the s-domain node admittance matrix is obtained;Current is injected at the point of common coupling of the target offshore wind farm, and the node voltage of the point of common coupling of the target offshore wind farm is calculated, and then the s-domain equivalent impedance of the target offshore wind farm is obtained;According to the topology structure of offshore wind power grid-connected system, the s-domain equivalent circuit thereof is constructed, and then the s-domain node admittance matrix thereof is obtained;All the zeros of the determinant of the s-domain node admittance matrix of offshore wind power grid-connected system in the frequency band of interest and the corresponding best controllable and observable nodes are calculated;The resonance stability of offshore wind power grid-connected system is analyzed according to the zero point characteristics and the position of the best controllable and observable nodes, which can improve the efficiency of resonance stability analysis.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power system transmission and distribution, and particularly relates to a method, system, device and storage medium for maintaining the resonance stability of an offshore wind power grid-connected system. BACKGROUND

[0002] For many small-scale offshore wind farms, AC transmission has become the main way of offshore wind power grid connection due to its simplicity, economy and mature technology. For the analysis of the resonance stability of an offshore wind power grid-connected system with long-distance AC submarine cable transmission, the interaction of the power grid, long-distance AC submarine cable and offshore wind farm needs to be considered comprehensively. The capacitance effect of the AC submarine cable is significant, and there are a large number of power electronic devices with wide frequency band and fast response in the offshore wind farm, which will significantly affect the resonance characteristics of the offshore wind power grid-connected system.

[0003] The resonance stability analysis of a large system should use the s-domain node admittance matrix method, and its mathematical model is the s-domain node admittance matrix. The key to calculating the resonance mode is to solve the zero point of the determinant of the s-domain node admittance matrix, which does not have difficulty in dealing with systems containing distributed parameter elements and frequency-dependent parameter elements. When using the s-domain node admittance matrix method to analyze the resonance stability of an offshore wind power grid-connected system, for cases that do not need to study the internal resonance characteristics of the offshore wind farm, such as designing resonance suppression devices at the offshore wind farm point of common coupling, and studying the internal resonance characteristics of a certain offshore wind farm in an offshore wind power grid-connected system containing multiple offshore wind farms, the target offshore wind farm needs to be simplified for equivalence to reduce the order of the s-domain node admittance matrix, thereby improving the analysis efficiency.

[0004] Aggregation method reduces the complexity of wind farm modeling by retaining the original fan structure and reducing the number of fans, which is currently the main method for simplifying the equivalence of wind farms. Aggregation method can be divided into single-machine equivalence and multi-machine equivalence according to the number of equivalent units. Single-machine equivalence equates the wind farm to a single wind turbine, while multi-machine equivalence equates the wind farm to multiple wind turbines. Single-machine equivalence is more widely used in resonance stability analysis. Literature [TAN, S. H. The Influence of Aggregation Method on Subsynchronous Oscillation Characteristics of Grid-connected System[D]. Beijing: North China Electric Power University, 2023.] points out that the aggregation method will change the original interaction path and coupling relationship in the wind farm during the equivalence process, and the dynamic characteristics and output characteristics of the wind farm grid-connected point will also change, which will inevitably affect the resonance stability analysis. Literature [WANG, Y. J., WANG, H. F. Oscillation Stability and Parameter Stability Domain Analysis of Large-scale Direct-drive Wind Farm under DC Voltage Dynamic Time Scale[J]. Proceedings of the CSEE, 2021, 41(S1): 92-107.] discusses the influence of the difference of wind turbine active power and control parameters on single-machine equivalence, and points out that when the difference of wind turbine control parameters is large, the stability analysis conclusion based on single-machine model lacks accuracy. SUMMARY

[0005] To solve the problem of low efficiency of resonance stability analysis of offshore wind power grid-connected system, the purpose of the present application is to provide a resonance stability analysis method and system for offshore wind power grid-connected system that maintains the resonance mode, so as to solve the problem that the traditional aggregation method changes the resonance characteristics of the wind farm when simplifying the equivalence of the wind farm, and improve the efficiency of resonance stability analysis.

[0006] In the first aspect, the present application provides a resonance stability analysis method for offshore wind power grid-connected system that maintains the resonance mode, which comprises the following steps:

[0007] (1) Establishing the s-domain impedance model of each electrical device of the offshore wind farm in the offshore grid-connected system, specifically including the s-domain impedance model of the wind turbine, the s-domain impedance model of the transformer, the s-domain impedance model of the cable, etc.;

[0008] (2) Constructing the s-domain equivalent circuit of the target offshore wind farm according to the topological structure of the target offshore wind farm and the s-domain impedance model of each electrical device of the offshore wind farm, and then obtaining the s-domain node admittance matrix of the target offshore wind farm;

[0009] (3) Injecting current at the point of common connection of the target offshore wind farm, calculating the node voltage at the point of common connection of the target offshore wind farm, and obtaining the s-domain equivalent impedance of the target offshore wind farm according to the injected current, the node voltage at the point of common connection, and the s-domain node admittance matrix of the target offshore wind farm;

[0010] (4) Constructing the s-domain equivalent circuit of the offshore wind power grid-connected system according to the topology of the offshore wind power grid-connected system and the s-domain equivalent impedance of the target offshore wind farm, and then obtaining the s-domain node admittance matrix of the offshore wind power grid-connected system;

[0011] (5) Calculating all the zeros of the determinant of the s-domain node admittance matrix of the offshore wind power grid-connected system and the corresponding optimal controllable and observable nodes in the concerned frequency band;

[0012] (6) Analyzing the resonance stability of the offshore wind power grid-connected system according to the zero characteristics and the position of the optimal controllable and observable nodes.

[0013] Further, the s-domain impedance model of the wind turbine in step (1) can be established using the test signal method, and the specific steps are as follows: after the wind turbine enters a steady state, a sinusoidal disturbance voltage signal of a certain frequency in the concerned frequency band is applied to the grid-connected point of the wind turbine for 1 second, the amplitude of the signal is not greater than 5% of the amplitude of the voltage at the grid-connected point of the wind turbine in the steady state, and the current signal of the wind turbine at the grid-connected point in the time is recorded; the current signal is subtracted from the steady-state current of the wind turbine at the grid-connected point before the sinusoidal disturbance voltage signal is applied; finally, the disturbance current signal of the wind turbine under the excitation of the sinusoidal disturbance voltage signal is obtained; the time domain data of the sinusoidal disturbance voltage signal and the disturbance current signal are converted into frequency domain data by FFT analysis, and the ratio of the sinusoidal disturbance voltage signal and the disturbance current signal in the frequency domain is the impedance value of the wind turbine at the frequency; discrete frequency points are taken in the concerned frequency band at a certain step, and the above method is repeated at each frequency point; the frequency domain impedance model of the wind turbine in the concerned frequency band is obtained by data fitting, and then the s-domain impedance model of the wind turbine in the concerned frequency band is obtained according to the corresponding relationship between the frequency domain and the s-domain.

[0014] Further, the s-domain impedance model of the transformer in step (1) is:

[0015]

[0016] In the formula: f0 is the fundamental frequency; X0 is the leakage reactance of the transformer at the fundamental frequency; S N is the rated capacity of the transformer.

[0017] Further, the specific establishment steps of the cable s-domain impedance model in step (1) are as follows: calculating the unit length impedance parameter, considering the frequency variation characteristic of the parameter, constructing the full-dimensional series impedance matrix according to the geometric parameter, transforming the full-dimensional series impedance matrix into different three-phase series impedance matrices according to different grounding modes of the cable, obtaining the sequence impedance matrix through sequence transformation of the three-phase series impedance matrix, only considering the unit length positive sequence impedance, repeating the above calculation process at each frequency point in the frequency band of interest; calculating the unit length admittance parameter, ignoring the parameter frequency variation characteristic and the line conductance, calculating the unit length capacitance according to the geometric parameter; calculating the whole line parameter, considering the parameter distribution characteristic, establishing the accurate pi model; converting the resistance, inductance and capacitance in the accurate pi model into the s-domain expression form, and the cable s-domain impedance model is obtained.

[0018] Further, in step (2), when the s-domain equivalent circuit of the target offshore wind farm is established, the s-domain impedance models of each electrical equipment of the target offshore wind farm need to be reduced to the basic voltage level. The basic voltage level is generally selected as the voltage level of the submarine cable in the target offshore wind farm.

[0019] Further, the specific establishment steps of the s-domain node admittance matrix of the target offshore wind farm in step (2) are as follows:

[0020] The nodes of the s-domain equivalent circuit of the target offshore wind farm are numbered as 0, 1, 2, …, (N-1), wherein the node number of the point of common coupling is 0, and N is the number of nodes of the target offshore wind farm.

[0021] The main diagonal elements in the s-domain node admittance matrix represent the self-admittance values of the corresponding nodes, the remaining elements represent the mutual admittance values between the nodes, and the subscripts of each element represent the node number; each element in the matrix is added to the corresponding matrix element according to the nodes connected by the element; when an element with an s-domain impedance Z1 is connected to the i node, the influence of the element on the s-domain node admittance matrix of the target offshore wind farm is to make Y ii and Y jj and Y kk and Y jk and Y kj add (-1 / Z2); the form of the s-domain node admittance matrix of the target offshore wind farm is as follows:

[0022]

[0023] The s-domain node admittance matrix of the target offshore wind farm is divided as follows:

[0024]

[0025]

[0026] Y0(s) is the s-domain branch admittance vector between the point of common connection and other nodes in the target offshore wind farm; Y(s) is the s-domain node admittance matrix of the target offshore wind farm except the point of common connection.

[0027] Further, in step (3), the specific calculation steps of the s-domain equivalent impedance of the target offshore wind farm are as follows:

[0028] Only the current i0(s) is injected at the point of common connection of the target offshore wind farm;

[0029] The node voltage equation of the target offshore wind farm is established:

[0030]

[0031] v(s) is the s-domain node voltage vector of the target offshore wind farm; i(s) is the s-domain node injected current vector of the target offshore wind farm;

[0032] The node voltage equation of the target offshore wind farm is transformed to:

[0033]

[0034] v’(s) is the s-domain node voltage vector of the target offshore wind farm except the point of common connection;

[0035] The node voltage v0(s) at the point of common connection of the target offshore wind farm is:

[0036]

[0037] The s-domain equivalent impedance Z e w q ind (s) of the target offshore wind farm is:

[0038]

[0039] Further, in step (4), when establishing the s-domain equivalent circuit of the offshore wind power grid-connected system, the s-domain impedance models of each electrical equipment in the offshore wind power grid-connected system except the offshore wind farm need to be calculated to the basic voltage level; when there are multiple offshore wind farms in the offshore wind power grid-connected system, the s-domain equivalent impedances of different offshore wind farms need to be calculated to the same basic voltage level; the basic voltage level is generally selected as the voltage level of the submarine cable in a certain offshore wind farm.

[0040] Further, in step (5), the calculation of the zero point of the s-domain node admittance matrix of the offshore wind farm grid-connected system is based on the decoupling characteristics of the real part and the imaginary part of the zero point corresponding to the resistance and the reactance, and thus mainly includes the following two stages:

[0041] Stage 1: In the undamped system with all element resistances being 0, the s-domain node admittance matrix of the offshore wind farm grid-connected system is transformed into an s-domain node susceptance matrix, the zero point of the s-domain node susceptance matrix is a real number and is close to the imaginary part of the zero point of the s-domain node admittance matrix, the zero point of the s-domain node susceptance matrix in the concerned frequency band is calculated, and thus the number of the zero points of the s-domain node admittance matrix in the concerned frequency band is determined, and further the node voltage mode is determined to obtain the best controllable and observable node.

[0042] Stage 2: In the complete system considering all element resistances, the zero point of the s-domain node admittance matrix is accurately calculated by using the test signal method at the best controllable and observable node.

[0043] Further, in step (6), whether the zero point of the s-domain node admittance matrix of the offshore wind farm grid-connected system can represent the resonance mode of the offshore wind farm grid-connected system is determined according to the position of the best controllable and observable node: if the best controllable and observable node is located outside the target offshore wind farm, the corresponding zero point can represent part of the resonance mode of the offshore wind farm system; if the best controllable and observable node is the common connection point of the target offshore wind farm, the corresponding zero point cannot represent the resonance mode of the offshore wind farm system.

[0044] Further, in step (6), the real part of the zero point representing the resonance mode of the offshore wind farm system represents the damping characteristics of the resonance mode, when the real part is positive, the resonance mode is a divergent unstable resonance mode; when the real part is negative, the resonance mode is an attenuated stable resonance mode; the imaginary part of the zero point represents the resonance angular frequency of the resonance mode; when all the resonance modes of the offshore wind farm grid-connected system are stable resonance modes, the offshore wind farm grid-connected system is stable in the concerned frequency band, otherwise there is a resonance risk and resonance suppression is needed.

[0045] In a second aspect, the present application provides a system for maintaining the resonance stability of an offshore wind farm grid-connected system, which is used to implement the method for analyzing the resonance stability of the offshore wind farm grid-connected system, and includes:

[0046] An impedance model establishing unit is configured to establish the s-domain impedance models of the electrical equipment of the offshore wind farm in the offshore wind farm grid-connected system, including the s-domain impedance models of the wind turbine, the transformer and the cable.

[0047] The offshore wind farm s-domain node admittance matrix construction unit: constructing an equivalent s-domain circuit of the target offshore wind farm according to the topological structure of the target offshore wind farm and s-domain impedance models of electrical equipment of the target offshore wind farm, and then obtaining an s-domain node admittance matrix of the target offshore wind farm;

[0048] The offshore wind farm s-domain equivalent impedance acquisition unit: injecting a current at a point of common coupling of the target offshore wind farm, calculating a node voltage at the point of common coupling, and obtaining an s-domain equivalent impedance of the target offshore wind farm according to the injected current, the node voltage, and the s-domain node admittance matrix of the target offshore wind farm;

[0049] The offshore wind farm s-domain node admittance matrix construction unit: constructing an equivalent s-domain circuit of the target offshore wind farm according to the topological structure of the target offshore wind farm and s-domain impedance models of electrical equipment of the target offshore wind farm, and then obtaining an s-domain node admittance matrix of the target offshore wind farm;

[0050] The zero point and optimal controllable and observable node calculation unit: calculating all zero points of a determinant of the s-domain node admittance matrix of the offshore wind farm grid-connected system and corresponding optimal controllable and observable nodes in a frequency band of interest.

[0051] The resonance stability analysis unit: analyzing resonance stability of the offshore wind farm grid-connected system according to the zero point characteristics and the positions of the optimal controllable and observable nodes.

[0052] In a third aspect, the present application provides a computer device, which comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor implements the steps of the offshore wind farm impedance equivalent modeling method when executing the computer program.

[0053] In a fourth aspect, the present application provides a computer readable storage medium, which stores a computer program, and the computer program implements the steps of the offshore wind farm impedance equivalent modeling method when executed by a processor.

[0054] Compared with the prior art, the present application has the following beneficial effects: the offshore grid-connected system topology under the interaction of multiple electrical equipment is fully considered, and the resonance stability analysis is more comprehensive; the order of the s-domain node admittance matrix of the whole system is reduced under the premise of maintaining the resonance mode, which greatly improves the speed of resonance stability analysis, especially in an offshore wind farm grid-connected system comprising multiple offshore wind farms; the impedance equivalent modeling process is mainly through the transformation of the node admittance matrix and the node voltage equation, and does not depend on the topology and scale of the network, and has universality. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 A flowchart of the offshore wind farm grid-connected system resonance stability analysis method of the present application for maintaining the resonance mode.

[0056] Figure 2 The structure diagram of the offshore wind power grid-connected system resonance stability analysis system for maintaining the resonance mode of the present application;

[0057] Figure 3 The structure diagram of the offshore wind power grid-connected system analyzed in the application example;

[0058] Figure 4 The complete s-domain equivalent circuit schematic diagram of the offshore wind power grid-connected system analyzed in the application example;

[0059] Figure 5 The s-domain equivalent circuit schematic diagram of the offshore wind power grid-connected system analyzed in the application example after the impedance equivalence of the target offshore wind farm;

[0060] Figure 6 The logic structure schematic diagram of the electronic device provided by the embodiment of the present application. DETAILED DESCRIPTION

[0061] In order to describe the present application more specifically, the technical solutions of the present application are described in detail below in combination with the drawings of the specification and the specific embodiments.

[0062] Embodiment 1

[0063] As shown in the description, Figure 1 The resonance stability analysis method of the offshore wind power grid-connected system for maintaining the resonance mode of the present application includes the following steps:

[0064] (1) Establish the s-domain impedance model of each electrical device of the offshore wind farm in the offshore wind power grid-connected system, specifically including the s-domain impedance model of the wind turbine generator, the s-domain impedance model of the transformer, the s-domain impedance model of the cable, etc.

[0065] The wind turbine s-domain impedance model can be established using a test signal method, and the specific steps are as follows: after the wind turbine enters a steady state, a sinusoidal disturbance voltage signal at a frequency in a frequency band of interest is applied to the wind turbine grid connection point for 1 second, the amplitude of the signal is not greater than 5% of the amplitude of the wind turbine grid connection point voltage in the steady state, and the current signal of the wind turbine grid connection point in the time is recorded, the current signal is subtracted from the steady-state current of the wind turbine grid connection point before the sinusoidal disturbance voltage signal is applied, and finally the disturbance current signal of the wind turbine under the excitation of the sinusoidal disturbance voltage signal is obtained; the time domain data of the sinusoidal disturbance voltage signal and the disturbance current signal are converted into frequency domain data by FFT analysis, and the ratio of the sinusoidal disturbance voltage signal and the disturbance current signal in the frequency domain is the impedance value of the wind turbine at the frequency; discrete frequency points are taken in the frequency band of interest at a certain step size, and the above method is repeated at each frequency point; the frequency domain impedance model of the wind turbine in the frequency band of interest is obtained by data fitting, and then the s-domain impedance model of the wind turbine in the frequency band of interest is obtained according to the corresponding relationship between the frequency domain and the s-domain.

[0066] The transformer s-domain impedance model is:

[0067]

[0068] In the formula, f0 is the fundamental frequency; X0 is the leakage reactance of the transformer at the fundamental frequency; S N is the rated capacity of the transformer.

[0069] The specific establishment steps of the cable s-domain impedance model are as follows: calculate the unit length impedance parameter, consider the frequency variation characteristic of the parameter, construct the full-dimensional series impedance matrix according to the geometric parameter, and transform the full-dimensional series impedance matrix into different three-phase series impedance matrices according to different grounding modes of the cable, obtain the sequence impedance matrix through sequence transformation of the three-phase series impedance matrix, only consider the unit length positive sequence impedance, and repeat the above calculation process at each frequency point in the frequency band of interest; calculate the unit length admittance parameter, ignore the frequency variation characteristic of the parameter and the line conductance, and calculate the unit length capacitance according to the geometric parameter; calculate the whole line parameter, consider the parameter distribution characteristic, and establish an accurate pi model; convert the resistance, inductance and capacitance in the accurate pi model into an s-domain expression form, and the s-domain impedance model of the cable is obtained.

[0070] (2) According to the topological structure of the target offshore wind farm, the s-domain equivalent circuit of the target offshore wind farm is constructed, and the s-domain node admittance matrix of the target offshore wind farm is obtained. When establishing the s-domain equivalent circuit of the target offshore wind farm, the s-domain impedance models of all electrical equipment in the target offshore wind farm need to be reduced to the basic voltage level, and the basic voltage level is generally selected as the voltage level of the submarine cable in the target offshore wind farm.

[0071] The specific establishment steps of the s-domain node admittance matrix of the target offshore wind farm are as follows:

[0072] The nodes of the target offshore wind farm s-domain equivalent circuit are numbered as 0, 1, 2, …, (N-1), wherein the node number of the point of common coupling is 0, and N is the number of nodes of the target offshore wind farm;

[0073] The main diagonal elements in the s-domain node admittance matrix represent the self-admittance values of the corresponding nodes, and the remaining elements represent the mutual admittance values between the nodes, and the subscript of each element represents the node number; each element in the s-domain node admittance matrix is obtained by traversing each element in the offshore wind farm and adding it to the corresponding matrix element according to the nodes connected by the element; when an element with an s-domain impedance of Z1 is connected to the i node, the influence of the element on the s-domain node admittance matrix of the target offshore wind farm is to make Y ii add 1 / Z1; when an element with an s-domain impedance of Z2 is connected between the j node and the k node, the influence of the element on the s-domain node admittance matrix of the target offshore wind farm is to make Y jj and Y kk add 1 / Z2, and Y jk and Y kj add (-1 / Z2); the form of the s-domain node admittance matrix of the target offshore wind farm is as follows:

[0074]

[0075] The s-domain node admittance matrix of the target offshore wind farm is divided as follows:

[0076]

[0077] In the formula, Y0(s) is an s-domain branch admittance vector between the point of common coupling and other nodes in the target offshore wind farm; is the s-domain node admittance matrix of the target offshore wind farm except for the point of common coupling.

[0078] (3) Injecting a current at the point of common coupling of the target offshore wind farm, calculating the node voltage at the point of common coupling of the target offshore wind farm, and obtaining the s-domain equivalent impedance of the target offshore wind farm according to the injected current, the node voltage and the s-domain node admittance matrix of the target offshore wind farm, the specific steps are as follows:

[0079] Only injecting a current i0(s) at the point of common coupling of the target offshore wind farm;

[0080] The node voltage equation of the target offshore wind farm is established as follows:

[0081]

[0082] In the formula, v(s) is an s-domain node voltage vector of the target offshore wind farm, and i(s) is an s-domain node injected current vector of the target offshore wind farm;

[0083] The node voltage equation of the target offshore wind farm is transformed as:

[0084]

[0085] In the formula, v'(s) is the s-domain node voltage vector of the target offshore wind farm except for the common connection point;

[0086] The node voltage v0(s) of the common connection point of the target offshore wind farm is obtained as:

[0087]

[0088] The s-domain equivalent impedance of the target offshore wind farm is

[0089]

[0090] (4) The s-domain impedance models of each electrical equipment in the offshore wind power grid-connected system except for the offshore wind farm are reduced to the basic voltage level; when there are multiple offshore wind farms in the offshore wind power grid-connected system, the s-domain equivalent impedances of different offshore wind farms need to be reduced to the same basic voltage level; the basic voltage level is generally selected as the voltage level of the submarine cable in a certain offshore wind farm. The s-domain equivalent circuit of the offshore wind power grid-connected system is constructed according to the topological structure of the offshore wind power grid-connected system, and then the s-domain node admittance matrix thereof is obtained.

[0091] (5) All the zeros of the s-domain node admittance matrix of the offshore wind power grid-connected system in the concerned frequency band are calculated; the zeros are based on the decoupling characteristics of the real part and the imaginary part corresponding to the resistance and the reactance, and thus are mainly divided into the following two stages:

[0092] The first stage: in the undamped system in which the resistances of all elements are 0, the s-domain node admittance matrix of the offshore wind power grid-connected system is transformed into the s-domain node susceptance matrix, the zeros of the s-domain node susceptance matrix are real numbers and close to the imaginary part of the zeros of the s-domain node admittance matrix, the zeros of the s-domain node susceptance matrix in the concerned frequency band are calculated, so as to determine the number of the zeros of the s-domain node admittance matrix in the concerned frequency band, and further to determine the node voltage mode, so as to obtain the best controllable and observable node.

[0093] The second stage: in the complete system considering the resistances of all elements, the zeros of the s-domain node admittance matrix are accurately calculated at the best controllable and observable node using the test signal method.

[0094] (6) The resonance stability of the offshore wind power grid-connected system is analyzed according to the zero characteristics and the position of the best controllable and observable node.

[0095] ​According to the position of the optimal controllable and observable node, it is judged whether the zero point of the s-domain node admittance matrix determinant of the offshore wind power grid-connected system can represent the resonance mode of the offshore wind power grid-connected system: if the optimal controllable and observable node is located outside the target offshore wind farm, the corresponding zero point can represent part of the resonance mode of the offshore wind power system; if the optimal controllable and observable node is the common connection point of the target offshore wind farm, the corresponding zero point cannot represent the resonance mode of the offshore wind power system.

[0096] For the zero point representing the resonance mode of the offshore wind power system, the real part represents the damping characteristic of the resonance mode. When the real part is positive, the resonance mode is a divergent unstable resonance mode; when the real part is negative, the resonance mode is an attenuated stable resonance mode; the imaginary part of the zero point represents the resonance angular frequency of the resonance mode; when all the resonance modes of the offshore wind power grid-connected system are stable resonance modes, the offshore wind power grid-connected system is stable in the concerned frequency band, otherwise there is a resonance risk and resonance suppression is needed.

[0097] Embodiment 2

[0098] This embodiment provides a kind of offshore wind power grid-connected system resonance stability analysis system for maintaining resonance mode, as shown in Fig. Figure 2 It is composed of impedance model establishing unit, offshore wind farm s-domain node admittance matrix construction unit, offshore wind farm s-domain equivalent impedance acquisition unit, offshore wind power grid-connected system s-domain node admittance matrix acquisition unit, zero point and optimal controllable and observable node calculation unit and resonance stability analysis unit.

[0099] (1) Impedance model establishing unit: for establishing the s-domain impedance model of each electrical equipment in the offshore wind power grid-connected system, including the s-domain impedance model of wind turbine generator, the s-domain impedance model of transformer and the s-domain impedance model of cable.

[0100] In the impedance model establishing unit, the wind turbine s-domain impedance model can be established by using a test signal method, and the specific steps are as follows: after the wind turbine enters a steady state, a sinusoidal disturbance voltage signal at a frequency in a concerned frequency band is applied to the wind turbine grid-connected point for 1 second, the amplitude of the signal is not greater than 5% of the amplitude of the voltage at the wind turbine grid-connected point in the steady state, and the current signal of the wind turbine grid-connected point in the time is recorded; the current signal is subtracted from the steady-state current of the wind turbine grid-connected point in the same time before the sinusoidal disturbance voltage signal is applied, and finally the disturbance current signal of the wind turbine under the excitation of the sinusoidal disturbance voltage signal is obtained; the time domain data of the sinusoidal disturbance voltage signal and the disturbance current signal are converted into frequency domain data by FFT analysis, and the ratio of the sinusoidal disturbance voltage signal and the disturbance current signal in the frequency domain is the impedance value of the wind turbine at the frequency; discrete frequency points are taken in the concerned frequency band at a certain step, and the above method is repeated at each frequency point; the frequency domain impedance model of the wind turbine in the concerned frequency band is obtained through data fitting, and then the s-domain impedance model of the wind turbine in the concerned frequency band is obtained according to the corresponding relationship between the frequency domain and the s-domain.

[0101] The transformer s-domain impedance model is:

[0102]

[0103] In the formula, f0 is the fundamental frequency; X0 is the leakage reactance of the transformer at the fundamental frequency; S N is the rated capacity of the transformer.

[0104] The steps for establishing the s-domain impedance model of the cable are as follows: calculate the unit length impedance parameter, consider the frequency variation characteristic of the parameter, construct the full-dimensional series impedance matrix according to the geometric parameter, transform the full-dimensional series impedance matrix into different three-phase series impedance matrices according to different grounding modes of the cable, obtain the sequence impedance matrix through sequence transformation of the three-phase series impedance matrix, only consider the unit length positive sequence impedance, and repeat the above calculation process at each frequency point in the concerned frequency band; calculate the unit length admittance parameter, ignore the frequency variation characteristic and line conductance of the parameter, and calculate the unit length capacitance according to the geometric parameter; calculate the whole line parameter, consider the parameter distribution characteristic, and establish an accurate pi model; convert the resistance, inductance and capacitance in the accurate pi model into an s-domain expression form, and thus the s-domain impedance model of the cable is obtained.

[0105] (2) The s-domain node admittance matrix construction unit of the offshore wind farm: the s-domain equivalent circuit of the target offshore wind farm is constructed according to the topological structure of the target offshore wind farm, and then the s-domain node admittance matrix of the target offshore wind farm is obtained.

[0106] When the s-domain equivalent circuit of the target offshore wind farm is established, the s-domain impedance models of all electrical equipment of the target offshore wind farm need to be reduced to the basic voltage level, and the basic voltage level is generally selected as the voltage level of the submarine cable in the target offshore wind farm.

[0107] The specific establishment steps of the target offshore wind farm s-domain node admittance matrix are as follows:

[0108] The nodes of the target offshore wind farm s-domain equivalent circuit are numbered as 0, 1, 2, …, (N-1), wherein the node number of the point of common connection is 0, and N is the number of nodes of the target offshore wind farm;

[0109] The main diagonal elements in the s-domain node admittance matrix represent the self-admittance values of the corresponding nodes, and the remaining elements represent the mutual admittance values between the nodes, and the subscripts of the elements represent the node numbers; each element in the offshore wind farm is traversed, and is added to the corresponding matrix element according to the nodes connected to the element; when an element with an s-domain impedance of Z1 is connected to the i node, the influence of the element on the target offshore wind farm s-domain node admittance matrix is to make Y ii add 1 / Z1; when an element with an s-domain impedance of Z2 is connected between the j node and the k node, the influence of the element on the target offshore wind farm s-domain node admittance matrix is to make Y jj and Y kk add 1 / Z2, and Y jk and Y kj add (-1 / Z2); the form of the target offshore wind farm s-domain node admittance matrix is:

[0110]

[0111] The target offshore wind farm s-domain node admittance matrix is divided as follows:

[0112]

[0113] In the formula, Y0(s) is an s-domain branch admittance vector between the point of common connection and other nodes in the target offshore wind farm; is the target offshore wind farm s-domain node admittance matrix except for the point of common connection.

[0114] (3) The offshore wind farm s-domain equivalent impedance acquisition unit: injecting a current at the point of common connection of the target offshore wind farm, calculating the node voltage of the point of common connection of the target offshore wind farm, and obtaining the s-domain equivalent impedance of the target offshore wind farm according to the injected current, the node voltage of the point of common connection, and the target offshore wind farm s-domain node admittance matrix.

[0115] The specific calculation steps of the s-domain equivalent impedance of the target offshore wind farm are as follows:

[0116] Only injecting a current i0(s) at the point of common connection of the target offshore wind farm;

[0117] The node voltage equation of the target offshore wind farm is established:

[0118]

[0119] where v(s) is the s-domain node voltage vector of the target offshore wind farm; i(s) is the s-domain node injection current vector of the target offshore wind farm;

[0120] The node voltage equation of the target offshore wind farm is transformed as follows:

[0121]

[0122] where v'(s) is the s-domain node voltage vector of the target offshore wind farm except for the point of common coupling;

[0123] The node voltage v0(s) of the point of common coupling of the target offshore wind farm is obtained as follows:

[0124]

[0125] The s-domain equivalent impedance of the target offshore wind farm is

[0126]

[0127] (4) The s-domain node admittance matrix construction unit of the offshore wind power grid-connected system: the s-domain equivalent circuit of the offshore wind power grid-connected system is constructed according to the topological structure of the offshore wind power grid-connected system and the s-domain equivalent impedance of the target offshore wind farm, and then the s-domain node admittance matrix of the offshore wind power grid-connected system is obtained.

[0128] When the s-domain equivalent circuit of the offshore wind power grid-connected system is established, the s-domain impedance models of each electrical device in the offshore wind power grid-connected system except for the offshore wind farm need to be reduced to the basic voltage level; when there are multiple offshore wind farms in the offshore wind power grid-connected system, the s-domain equivalent impedances of different offshore wind farms need to be reduced to the same basic voltage level; the basic voltage level is generally selected as the voltage level of the submarine cable in a certain offshore wind farm.

[0129] (5) The zero point and the best controllable and observable node calculation unit: all zero points and corresponding best controllable and observable nodes of the determinant of the s-domain node admittance matrix of the offshore wind power grid-connected system in the concerned frequency band are calculated.

[0130] The zero point calculation of the determinant of the s-domain node admittance matrix of the offshore wind power grid-connected system is based on the decoupling characteristics of the real part and the imaginary part of the zero point corresponding to the resistance and the reactance, and mainly includes the following two stages:

[0131] ​Phase 1: In the undamped system with all element resistances being 0, the s-domain node admittance matrix of the offshore wind power grid-connected system is transformed into an s-domain node susceptance matrix, the zero point of the determinant of the s-domain node susceptance matrix is a real number and close to the imaginary part of the zero point of the determinant of the s-domain node admittance matrix, the zero point of the determinant of the s-domain node susceptance matrix in the concerned frequency band is calculated, thereby the number of the zero points of the determinant of the s-domain node admittance matrix in the concerned frequency band is determined, and the node voltage mode is further determined to obtain the best controllable and observable node.

[0132] Phase 2: In the complete system considering all element resistances, the zero point of the determinant of the s-domain node admittance matrix is accurately calculated using the test signal method at the best controllable and observable node.

[0133] (6) Resonance stability analysis unit: the resonance stability of the offshore wind power grid-connected system is analyzed according to the zero point characteristics and the position of the best controllable and observable node.

[0134] The position of the best controllable and observable node is used to determine whether the zero point of the determinant of the s-domain node admittance matrix of the offshore wind power grid-connected system can represent the resonance mode of the offshore wind power grid-connected system: if the best controllable and observable node is located outside the target offshore wind farm, the corresponding zero point can represent part of the resonance mode of the offshore wind power system; if the best controllable and observable node is the common connection point of the target offshore wind farm, the corresponding zero point cannot represent the resonance mode of the offshore wind power system.

[0135] The zero point that can represent the resonance mode of the offshore wind power system has a real part representing the damping characteristics of the resonance mode, when the real part is positive, the resonance mode is a divergent unstable resonance mode; when the real part is negative, the resonance mode is a decaying stable resonance mode; the imaginary part of the zero point represents the resonance angular frequency of the resonance mode; when all the resonance modes of the offshore wind power grid-connected system are stable resonance modes, the offshore wind power grid-connected system is stable in the concerned frequency band, otherwise there is a resonance risk and resonance suppression is needed.

[0136] Application example

[0137] Taking a certain offshore wind power grid-connected system as an example, the structure diagram thereof is shown in Figure 3 The impedance equivalent modeling of the offshore wind farm contained therein is performed, and the resonance stability of the offshore wind power grid-connected system is analyzed.

[0138] The s-domain impedance models of various electrical devices in the offshore wind farm of the offshore wind power grid-connected system are established, including the s-domain impedance model of a wind turbine, the s-domain impedance model of a transformer, and the s-domain impedance model of a cable. The wind turbine includes a doubly-fed wind turbine and a direct-drive wind turbine, and the s-domain impedance model of the wind turbine is established by using a test signal method. The transformer includes a step-up transformer at the outlet of the wind turbine and an offshore step-up transformer at the bus, and the s-domain impedance model of the transformer is established according to the fundamental frequency parameters. The cable includes a three-core cable, a single-core submarine cable, and a single-core land cable, and the s-domain impedance model of the cable is established based on an accurate pi model by considering the frequency variation characteristics and the distribution characteristics.

[0139] The s-domain impedance models of various electrical devices in the offshore wind farm are all reduced to the basic voltage level, and the basic voltage level is generally selected as the voltage level of the submarine cable in the offshore wind farm. The s-domain equivalent circuit of the offshore wind farm is constructed according to the topological structure of the offshore wind farm, as shown in FIG. 2. Figure 4 The nodes of the s-domain equivalent circuit of the offshore wind farm are renumbered, and then the s-domain node admittance matrix of the offshore wind farm is obtained, and the s-domain node admittance matrix is blocked.

[0140] The current is injected at the point of common coupling of the offshore wind farm, the node voltage equation of the offshore wind farm is established, the node voltage at the point of common coupling of the offshore wind farm is calculated by transforming the node voltage equation, and then the s-domain equivalent impedance of the offshore wind farm is obtained.

[0141] The s-domain impedance models of various electrical devices in the offshore wind power grid-connected system except the offshore wind farm are reduced to the basic voltage level. Since there is only one offshore wind farm in the offshore wind power grid-connected system, the basic voltage level is selected as the voltage level of the submarine cable in the offshore wind farm. The s-domain equivalent circuit of the offshore wind power grid-connected system is constructed according to the topological structure of the offshore wind power grid-connected system, as shown in FIG. 3. Figure 5 The s-domain node admittance matrix of the offshore wind power grid-connected system is obtained.

[0142] The s-domain node admittance matrix of the offshore wind power grid-connected system is obtained.

[0143] The calculation results of the zero points of the s-domain node admittance matrix of the offshore wind power grid-connected system analyzed in the application examples are shown in Table 1.

[0144] Table 1

[0145]

[0146] The s-domain node admittance matrix of the offshore wind power grid-connected system has two zero points. The value of zero point 1 before and after impedance equivalence is basically unchanged, the optimal controllable and observable node of zero point 1 after impedance equivalence is located outside the target offshore wind farm, so that zero point 1 after impedance equivalence can represent the resonance mode of the offshore wind power system; the value of zero point 2 before and after impedance equivalence is quite different, the optimal controllable and observable node of zero point 2 after impedance equivalence is the common connection point of the target offshore wind farm, so that zero point 2 after impedance equivalence cannot represent the resonance mode of the offshore wind power system. In addition, the zero point calculation results of the new impedance equivalence based on the s-domain node admittance matrix transformation introduced in the application and the traditional impedance equivalence using series-parallel and star-delta conversion are the same, which proves the effectiveness of the method introduced in the application. For zero point 1 representing the resonance mode of the offshore wind power system after impedance equivalence, the real part is negative, and the represented resonance mode is a stable resonance mode of decay.

[0147] Embodiment 3

[0148] The embodiment provides an electronic device, comprising: at least one processor; and a memory connected in communication with the at least one processor. The memory stores a computer program capable of being executed by the at least one processor, and the computer program, when executed by the at least one processor, is configured to cause the electronic device to perform the method according to the embodiment 1 of the application.

[0149] Embodiment 4

[0150] The embodiment provides a non-transitory computer readable storage medium storing a computer program, wherein the computer program, when executed by a processor of a computer, is configured to cause the computer to perform the method according to the embodiment 1 of the application.

[0151] Reference Figure 6 A block diagram of the structure of an electronic device 400 that can be a server or a client of the present application will now be described, which is an example of a hardware device that can be applied to aspects of the present application. The electronic device is intended to represent a wide variety of digital electronic computing devices, such as laptops, desktops, workstations, personal digital assistants, servers, blade servers, mainframes, and other suitable computing devices. The electronic device can also represent a wide variety of mobile devices, such as personal digital processing, cellular phones, smart phones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their functions, are meant to be examples only, and are not intended to limit the implementations of the present application described and / or claimed in this document.

[0152] As Figure 6As shown, the electronic device 400 includes a computing unit 401 that can perform various appropriate actions and processes in accordance with a computer program stored in a read-only memory (ROM) 402 or a computer program loaded into a random access memory (RAM) 403 from a storage unit 408. In the RAM 403, various programs and data required for the operation of the electronic device 400 can also be stored. The computing unit 401, the ROM 402, and the RAM 403 are connected to each other through a bus 404. An input / output (I / O) interface 405 is also connected to the bus 404.

[0153] A plurality of components in the electronic device 400 are connected to the I / O interface 405, including an input unit 406, an output unit 407, the storage unit 408, and a communication unit 409. The input unit 406 can be any type of device that can input information to the electronic device 400, and can receive inputted numerical or character information, as well as generate key signal inputs related to user settings and / or function controls of the electronic device. The output unit 407 can be any type of device that can present information, and can include, but is not limited to, a display, a speaker, a video / audio output terminal, a vibrator, and / or a printer. The storage unit 408 can include, but is not limited to, a magnetic disk, an optical disk. The communication unit 409 allows the electronic device 400 to exchange information / data with other devices through a computer network such as the Internet and / or various telecommunication networks, and can include, but is not limited to, a modem, a network card, an infrared communication device, a wireless communication transceiver, and / or a chipset, such as a Bluetooth™ device, a WiFi device, a WiMax device, a cellular communication device, and / or the like.

[0154] The computing unit 401 can be various general and / or special purpose processing components having processing and computing capabilities. Some examples of the computing unit 401 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various special-purpose artificial intelligence (AI) computing chips, various computing units running machine learning model algorithms, a digital signal processor (DSP), and any appropriate processor, controller, microcontroller, etc. The computing unit 401 performs the various methods and processes described above. For example, in some embodiments, the aforementioned metal corrosion prediction method can be implemented as a computer software program that is tangibly embodied in a machine-readable medium, such as the storage unit 408. In some embodiments, part or all of the computer program can be loaded and / or installed onto the electronic device 400 via the ROM 402 and / or the communication unit 409. In some embodiments, the computing unit 401 can be configured to perform the aforementioned metal corrosion prediction method by any other appropriate means, such as by means of firmware.

[0155] Program code for carrying out operations of the methods of the present application can be written in any combination of one or more programming languages. The program code can be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the program code, when executed by the processor or controller, produces the functions / operations specified in the flowcharts and / or block diagrams. The program code can be executed entirely on a machine, partially on a machine, partially on a machine as part of a separate software package, and partially on a remote machine or entirely on a remote machine or server.

[0156] In the context of the present application, a machine-readable medium can be a tangible medium that can contain or store program for use by or in connection with an instruction execution system, apparatus, or device. The machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. Machine-readable storage media can include, without limitation, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media can include an electrical connection based on one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0157] As used in the present application, the terms "machine-readable medium" and "computer-readable medium" refer to any computer program product, apparatus and / or device (e.g., magnetic discs, optical disks, memory, Programmable Logic Devices (PLDs)) used to provide machine instructions and / or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term "machine-readable signal" refers to any signal that can be used to provide machine instructions and / or data to a programmable processor.

[0158] To provide for interaction with a user, the systems and techniques described here can be implemented on a computer having a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball) by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0159] The systems and techniques described here can be implemented in a computing system that includes a back end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front end component, e.g., a user computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the systems and techniques described here, or any combination of such back end, middleware, or front end components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (LAN), a wide area network (WAN), and the Internet.

[0160] The computer system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

[0161] The foregoing description of the exemplary embodiments is provided as is for the purpose of enabling any persons skilled in the art who are not familiar with the technology to understand and apply the present application. It will be apparent to those skilled in the art that various modifications and changes can be made thereto without departing from the scope of the present application, which is set forth in the appended claims. Thus, it is intended that the present application encompass such modifications and changes as fall within the scope of the appended claims.

Claims

1. A method for analyzing the resonant stability of an offshore wind power grid-connected system, characterized in that, Including the following steps: Establish s-domain impedance models for various electrical equipment in offshore wind farms within the offshore wind power grid connection system, including s-domain impedance models for wind turbines, transformers, and cables; Based on the topology of the target offshore wind farm and the s-domain impedance model of each electrical device in the target offshore wind farm, the equivalent circuit of the target offshore wind farm in the s-domain is constructed, and then the node admittance matrix of the target offshore wind farm in the s-domain is obtained. Inject current into the point of common coupling of the target offshore wind farm, calculate the node voltage of the point of common coupling of the target offshore wind farm, and obtain the s-domain equivalent impedance of the target offshore wind farm based on the injected current, node voltage and s-domain node admittance matrix of the target offshore wind farm. Based on the topology of the offshore wind power grid connection system and the s-domain equivalent impedance of the target offshore wind farm, the s-domain equivalent circuit of the offshore wind power grid connection system is constructed, and then the s-domain node admittance matrix of the offshore wind farm grid connection system is obtained. Within the focus frequency band, calculate all zeros of the determinant of the s-domain node admittance matrix of the offshore wind power grid-connected system and the corresponding best controllable and observable node; The resonant stability of offshore wind power grid-connected systems is analyzed based on zero-point characteristics and the optimal controllable and observable node location.

2. The method according to claim 1, characterized in that, The s-domain impedance model of the wind turbine is established using the test signal method. The specific steps are as follows: After the wind turbine enters the steady-state operation, a sinusoidal disturbance voltage signal of a certain frequency within the focus frequency band is applied to the grid connection point of the wind turbine for a duration of 1 second. The amplitude of this signal is no greater than 5% of the voltage amplitude of the wind turbine grid connection point under steady-state operation. At the same time, the current signal of the wind turbine grid connection point is recorded during this time. The steady-state current of the wind turbine grid connection point during the same time before the sinusoidal disturbance voltage signal is applied is subtracted from this current signal to obtain the disturbance current signal of the wind turbine under the excitation of the sinusoidal disturbance voltage signal. The time-domain data of sinusoidal disturbance voltage and disturbance current signals are converted into frequency-domain data through FFT analysis. The ratio of the sinusoidal disturbance voltage signal to the disturbance current signal in the frequency domain is the impedance value of the wind turbine at that frequency. Discrete frequency points are taken in the frequency band of interest with a certain step size, and the above method is repeated at each frequency point. The frequency domain impedance model of the wind turbine in the frequency band of interest is obtained by data fitting. Then, according to the correspondence between the frequency domain and the s-domain, the s-domain impedance model of the wind turbine in the frequency band of interest is obtained.

3. The method according to claim 1, characterized in that, The steps for establishing the cable s-domain impedance model are as follows: Calculate the impedance parameters per unit length, considering the frequency-varying characteristics of the parameters, construct a full-dimensional series impedance matrix based on the geometric parameters, transform the full-dimensional series impedance matrix into different three-phase series impedance matrices according to different grounding methods of the cable, obtain the sequence impedance matrix from the three-phase series impedance matrix through sequence transformation, consider only the positive sequence impedance per unit length, and repeat the above calculation process at each frequency point within the frequency band of interest; calculate the admittance parameters per unit length, ignoring the frequency-varying characteristics of the parameters and the line conductance, and calculate the capacitance per unit length based on the geometric parameters; Calculate the overall line parameters, consider the parameter distribution characteristics, and establish an accurate π model; convert the resistance, inductance, and capacitance in the accurate π model into s-domain expressions to obtain the cable s-domain impedance model.

4. The method according to claim 1, characterized in that, The specific steps for establishing the nodal admittance matrix of the target offshore wind farm in the s-domain are as follows: The equivalent circuit nodes of the target offshore wind farm s domain are numbered as 0, 1, 2, ..., (N-1), where the node number of the common connection point is 0, and N is the number of nodes of the target offshore wind farm. In the s-domain node admittance matrix, the main diagonal elements represent the self-admittance values ​​of the corresponding nodes, and the remaining elements represent the mutual admittance values ​​between nodes. The subscript of each element represents the node number. Traverse each element in the offshore wind farm and add it to the corresponding matrix element according to the node to which the element is connected. When an element with an s-domain impedance of Z1 is connected to node i, its effect on the s-domain node admittance matrix of the target offshore wind farm is such that Y ii Add 1 / Z1; when an element with an s-domain impedance of Z2 is connected between node j and node k, its effect on the s-domain nodal admittance matrix of the target offshore wind farm is such that Y jj and Y kk Add 1 / Z2, and simultaneously make Y jk and Y kj Add (-1 / Z2); the form of the nodal admittance matrix of the target offshore wind farm in the s-domain is: The nodal admittance matrix of the target offshore wind farm in the s-domain is divided into the following blocks: In the formula: Y0(s) is the s-domain branch admittance vector between the common connection point and other nodes within the target offshore wind farm; Let be the admittance matrix of the target offshore wind farm s-domain nodes excluding the common connection point.

5. The method according to claim 4, characterized in that, The specific calculation steps for the s-domain equivalent impedance of the target offshore wind farm are as follows: Inject current i0(s) only at the point of common coupling of the target offshore wind farm; Establish the nodal voltage equations for the target offshore wind farm: In the formula: v(s) is the s-domain node voltage vector of the target offshore wind farm; i(s) is the s-domain node injected current vector of the target offshore wind farm. The nodal voltage equations for the target offshore wind farm are transformed to obtain: In the formula: v'(s) is the s-domain node voltage vector of the target offshore wind farm excluding the common connection point; The nodal voltage v0(s) at the point of common coupling of the target offshore wind farm is obtained as follows: s-domain equivalent impedance of the target offshore wind farm for:

6. The method according to claim 1, characterized in that, The zero-point calculation of the determinant of the s-domain node admittance matrix of an offshore wind power grid-connected system is based on the decoupling characteristics of the real and imaginary parts of the zeros with the resistance and reactance, respectively, and is mainly divided into the following two stages; Phase 1: In an undamped system where all component resistances are set to 0, the s-domain node admittance matrix of the offshore wind power grid-connected system is transformed into the s-domain node susceptance matrix. The zeros of the determinant of the s-domain node susceptance matrix are real numbers and close to the imaginary part of the zeros of the determinant of the s-domain node admittance matrix. The zeros of the determinant of the s-domain node susceptance matrix within the frequency band of interest are calculated to determine the number of zeros of the determinant of the s-domain node admittance matrix within the frequency band of interest. The node voltage mode shape is further determined to obtain the optimal controllable and observable node. Phase 2: In the complete system considering the resistance of all components, the zeros of the determinant of the nodal admittance matrix in the s-domain are accurately calculated using the test signal method at the optimal controllable and observable node.

7. The method according to claim 1, characterized in that, The location of the optimal controllable and observable node determines whether the zeros of the determinant of the s-domain node admittance matrix of the offshore wind power grid-connected system can characterize the resonant modes of the offshore wind power grid-connected system: if the optimal controllable and observable node is located outside the target offshore wind farm, then the corresponding zeros can characterize some of the resonant modes of the offshore wind power system; if the optimal controllable and observable node is the common connection point of the target offshore wind farm, then the corresponding zeros cannot characterize the resonant modes of the offshore wind power system.

8. A resonance stability analysis system for an offshore wind power grid-connected system, used to implement the method described in any one of claims 1 to 7, characterized in that, include: Impedance Model Establishment Unit: Used to establish the S-domain impedance models of various electrical equipment in the offshore wind farm in the offshore wind power grid connection system, including the S-domain impedance models of wind turbines, transformers, and cables. Offshore wind farm s-domain node admittance matrix construction unit: Based on the topology of the target offshore wind farm and the s-domain impedance model of each electrical device in the target offshore wind farm, construct the equivalent circuit of the target offshore wind farm in the s-domain, and then obtain the node admittance matrix of the target offshore wind farm in the s-domain. The s-domain equivalent impedance acquisition unit for offshore wind farms: Inject current into the common coupling point of the target offshore wind farm, calculate the node voltage of the common coupling point of the target offshore wind farm, and obtain the s-domain equivalent impedance of the target offshore wind farm based on the injected current, node voltage, and s-domain node admittance matrix of the target offshore wind farm. Unit for obtaining the s-domain node admittance matrix of offshore wind power grid-connected system: Based on the topology of the offshore wind power grid-connected system and the s-domain equivalent impedance of the target offshore wind farm, construct the s-domain equivalent circuit of the offshore wind power grid-connected system, and then obtain the s-domain node admittance matrix of the offshore wind power grid-connected system; Zero-point and best controllable and observable node calculation unit: Calculates all zero points and corresponding best controllable and observable nodes in the determinant of the s-domain node admittance matrix of the offshore wind power grid-connected system within the frequency band of interest; Resonance stability analysis unit: Analyzes the resonance stability of offshore wind power grid-connected systems based on zero-point characteristics and optimal controllable and observable node locations.

9. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

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