Offshore wind power grid-connected system resonance stability analysis method, system and equipment and storage medium

Abstract

The invention discloses an offshore wind power grid-connected system resonance stability analysis method, system and device and a storage medium. The method comprises the following steps: establishing an s-domain impedance model of each electrical device of the offshore wind power grid-connected system; an s-domain equivalent circuit is constructed according to the topological structure of the target offshore wind plant, and then an s-domain node admittance matrix is obtained; injecting current at the common connection point of the target offshore wind plant, calculating the node voltage of the common connection point of the target offshore wind plant, and further obtaining the s-domain equivalent impedance of the target offshore wind plant; an 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 an s-domain node admittance matrix is obtained; calculating all zero points of an s-domain node admittance matrix determinant of the offshore wind power grid-connected system and corresponding optimal controllable observable nodes in the concerned frequency band; the resonance stability of the offshore wind power grid-connected system is analyzed according to the zero point characteristic and the optimal controllable observable node position, and the resonance stability analysis efficiency can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power transmission and distribution of electric power systems, and specifically relates to a resonance stability analysis method, system, equipment and storage medium for an offshore wind power grid-connected system that maintains a resonance mode. Background Art

[0002] For many smaller offshore wind farms, AC power transmission has become the main way to connect offshore wind power to the grid due to its simplicity, economy and mature technology. To analyze the resonance stability of offshore wind power grid-connected systems transmitted via long-distance AC submarine cables, it is necessary to comprehensively consider the interaction between the power grid, long-distance AC submarine cables and offshore wind farms. The capacitance effect of AC submarine cables is significant, and there are a large number of wide-bandwidth and fast-response power electronic equipment in offshore wind farms, which will significantly affect the resonance characteristics of offshore wind power grid-connected systems.

[0003] The resonant stability analysis of large systems should use the s-domain node admittance matrix method, whose mathematical model is the s-domain node admittance matrix. The key to calculating the resonant mode is to solve the zero point of the determinant of the s-domain node admittance matrix, which has no difficulty in dealing with systems containing distributed parameter elements and frequency-variable parameter elements. When using the s-domain node admittance matrix method to analyze the resonant stability of offshore wind power grid-connected systems, for situations where there is no need to study the internal resonant characteristics of offshore wind farms, such as designing a resonant suppression device at the common connection point of an offshore wind farm, and studying the internal resonant characteristics of an offshore wind farm in an offshore wind power grid-connected system containing multiple offshore wind farms, it is necessary to perform equivalent simplification on the target offshore wind farm to reduce the order of the s-domain node admittance matrix, thereby improving the analysis efficiency.

[0004] The aggregation method reduces the complexity of wind farm modeling by retaining the original wind turbine structure and reducing the number of wind turbines. It is currently the main method for equivalent simplification of wind farms. The aggregation method can be divided into single-machine equivalence and multi-machine equivalence according to the number of equivalent units. The single-machine equivalence equates the wind farm to a wind turbine unit, while the multi-machine equivalence performs single-machine equivalence on a group of wind turbines with similar operating conditions, using multiple wind turbines to replace the wind farm. The single-machine equivalence is more widely used in resonant stability analysis. The literature [Tan Shangchen. Research on the influence of direct-drive wind farm aggregation equivalence on the subsynchronous oscillation characteristics of the 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 equivalent process. At the same time, the dynamic characteristics and output characteristics of the wind farm grid connection point will also change, which will inevitably have a certain impact on the resonant stability analysis. The literature [Wang Yijun, Wang Haifeng. Analysis of oscillation stability and parameter stability domain of large-scale direct-drive wind farms under the dynamic time scale of DC voltage [J]. Proceedings of the CSEE, 2021, 41(S1): 92-107.] discussed the impact of the differences in wind turbine active output and control parameters on the equivalent value of a single machine, and pointed out that when the differences in wind turbine control parameters are large, the stability analysis conclusions based on the single machine model lack accuracy. Summary of the invention

[0005] In order to address the problem of low efficiency in resonant stability analysis of offshore wind power grid-connected systems, the purpose of the present invention is to provide a resonant stability analysis method and system for offshore wind farm grid-connected systems that maintain resonant modes, so as to solve the problem that the traditional aggregation method will change the resonant characteristics of the wind farm when processing the equivalent simplification of the wind farm, while improving the efficiency of the resonant stability analysis.

[0006] In a first aspect, the present invention provides a method for analyzing the resonance stability of an offshore wind power grid-connected system maintaining a resonance mode, which comprises the following steps:

[0007] (1) Establish the s-domain impedance model of each electrical equipment in the offshore wind farm in the offshore grid-connected system, 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) According to the topological structure of the target offshore wind farm and the s-domain impedance model of each electrical equipment in the offshore wind farm, the s-domain equivalent circuit of the target offshore wind farm is constructed, and then the s-domain node admittance matrix of the target offshore wind farm is obtained;

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

[0010] (4) 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, the s-domain equivalent circuit of the offshore wind power grid-connected system is constructed, and then the s-domain node admittance matrix of the offshore wind power grid-connected system is obtained;

[0011] (5) Calculate all 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 within the frequency band of interest;

[0012] (6) Analyze the resonant stability of the offshore wind power grid-connected system based on the zero-point characteristics and the optimal controllable and observable node positions.

[0013] Furthermore, the wind turbine s-domain impedance model in step (1) can be established using a test signal method, and the specific steps are as follows: after the wind turbine enters a steady-state operation state, a sinusoidal disturbance voltage signal of a certain frequency in the frequency band of interest is applied at the wind turbine grid connection point for a duration of 1 second, and the amplitude of the signal is not greater than 5% of the voltage amplitude of the wind turbine grid connection point in the steady-state operation state. At the same time, the current signal of the wind turbine grid connection point during this time is recorded, and 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 the current signal, and finally the positive The disturbance current signal of the wind turbine generator set under the excitation of the sinusoidal disturbance voltage signal; the time domain data of the sinusoidal disturbance voltage signal and the disturbance current signal are converted into frequency domain data through FFT analysis, and 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 generator set at this frequency; discrete frequency points are taken at a certain step size in the frequency band of interest, and the above method is repeated at each frequency point; the frequency domain impedance model of the wind turbine generator set in the frequency band of interest is obtained through data fitting, and then the s-domain impedance model of the wind turbine generator set in the frequency band of interest is obtained according to the corresponding relationship between the frequency domain and the s-domain.

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

[0015]

[0016] Where: f 0 is the fundamental frequency; X 0 is the leakage reactance of the transformer at the fundamental frequency; S N is the rated capacity of the transformer.

[0017] Furthermore, the specific steps for establishing the cable S-domain impedance model in step (1) are as follows: calculate the impedance parameters per unit length, consider the frequency-varying characteristics of the parameters, construct a full-dimensional series impedance matrix according to the geometric parameters, transform the full-dimensional series impedance matrix into different three-phase series impedance matrices according to different cable grounding methods, and obtain the sequence impedance matrix through sequence transformation of the three-phase series impedance matrix, only consider the positive sequence impedance per unit length, and repeat the above calculation process at each frequency point in the frequency band of interest; calculate the admittance parameters per unit length, ignore the frequency-varying characteristics of the parameters and the line conductance, and calculate the capacitance per unit length according to the geometric parameters; calculate the entire 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 an S-domain expression to obtain the cable S-domain impedance model.

[0018] Furthermore, when establishing the s-domain equivalent circuit of the target offshore wind farm in step (2), the s-domain impedance models of the electrical equipment in the target offshore wind farm need to be converted 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] Furthermore, the specific steps for establishing the target offshore wind farm s-domain node admittance matrix 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), where the node number of the common connection point 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 value of the corresponding node, and the remaining elements represent the mutual admittance value 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 s-domain impedance is Z 1 When the element is connected to the i node, its influence on the target offshore wind farm s domain node admittance matrix is ​​to make Y ii Add 1 / Z 1 ; When an s-domain impedance is Z 2 When the element is connected between the j node and the k node, its influence on the node admittance matrix of the target offshore wind farm s domain is to make Y jj and Y kk Add 1 / Z 2 , while making Y jk and Y kj Add (-1 / Z 2 ); the form of the target offshore wind farm s domain node admittance matrix is:

[0022]

[0023] The s-domain node admittance matrix of the target offshore wind farm is divided into the following blocks:

[0024]

[0025]

[0026] Where: Y 0 (s) is the s-domain branch admittance vector between the common connection point and other nodes in the target offshore wind farm; is the admittance matrix of the target offshore wind farm s domain nodes except the public connection point.

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

[0028] The current i is injected only at the target offshore wind farm common connection point 0 (s);

[0029] Establish the node voltage equation of the target offshore wind farm:

[0030]

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

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

[0033]

[0034] Where: v'(s) is the voltage vector of the s-domain nodes of the target offshore wind farm except the common connection point;

[0035] Obtain the node voltage v of the common connection point of the target offshore wind farm 0 (s) is:

[0036]

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

[0038]

[0039] Furthermore, in step (4), when the s-domain equivalent circuit of the offshore wind power grid-connected system is established, the s-domain impedance model of each electrical equipment in the offshore wind power grid-connected system except the offshore wind farm needs to be converted 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 converted 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] Furthermore, in step (5), 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 and imaginary parts of the zero point corresponding to the resistance and reactance respectively, and is mainly divided into the following two stages:

[0041] 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 an s-domain node susceptance matrix. The zeros of the s-domain node susceptance matrix determinant are real numbers and close to the imaginary part of the zeros of the s-domain node admittance matrix determinant. The zeros of the s-domain node susceptance matrix determinant within the frequency band of interest are calculated, thereby determining the number of zeros of the s-domain node admittance matrix determinant within the frequency band of interest, and further determining the node voltage vibration mode to obtain the best controllable and observable node;

[0042] Phase 2: In the complete system considering all component resistances, the zeros of the determinant of the s-domain node admittance matrix are accurately calculated using the test signal method at the best controllable and observable nodes.

[0043] Furthermore, in step (6), it is determined 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 resonant mode of the offshore wind power grid-connected system 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 resonant 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 resonant mode of the offshore wind power system.

[0044] Furthermore, in step (6), the zero point of the resonant mode of the offshore wind power system can be characterized, and its real part represents the attenuation characteristics of the resonant mode. When the real part is positive, the resonant mode is a divergent unstable resonant mode; when the real part is negative, the resonant mode is an attenuated stable resonant mode; the imaginary part of the zero point represents the resonant angular frequency of the resonant mode; when all resonant modes of the offshore wind power grid-connected system are stable resonant modes, the offshore wind power grid-connected system is stable within the frequency band of interest, otherwise there is a resonance risk and resonance suppression is required.

[0045] In a second aspect, the present invention provides a resonant stability analysis system for an offshore wind power grid-connected system maintaining a resonant mode, which is used to implement the resonant stability analysis method for the offshore wind power grid-connected system, comprising:

[0046] Impedance model building unit: used to build the s-domain impedance model of each electrical equipment in the offshore wind farm in the offshore wind power grid-connected system, including the s-domain impedance model of the wind turbine, the s-domain impedance model of the transformer and the s-domain impedance model of the cable;

[0047] Offshore wind farm s-domain node admittance matrix construction unit: constructs the target offshore wind farm s-domain equivalent circuit according to the topological structure of the target offshore wind farm and the s-domain impedance model of each electrical equipment in the target offshore wind farm, and then obtains the target offshore wind farm s-domain node admittance matrix;

[0048] Offshore wind farm s-domain equivalent impedance acquisition unit: inject current into the common connection point of the target offshore wind farm, calculate the node voltage of the common connection point of the target offshore wind farm, and obtain the s-domain equivalent impedance of the target offshore wind farm according to the injected current, node voltage and s-domain node admittance matrix of the target offshore wind farm at the common connection point;

[0049] Offshore wind power grid-connected system s-domain node admittance matrix construction unit: constructs an offshore wind power grid-connected system s-domain equivalent circuit 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 obtains the offshore wind power grid-connected system s-domain node admittance matrix;

[0050] Zero point and best controllable and observable node calculation unit: calculate 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 within the frequency band of interest;

[0051] Resonance stability analysis unit: Analyze the resonance stability of offshore wind power grid-connected systems based on zero-point characteristics and optimal controllable and observable node positions.

[0052] In a third aspect, the present invention provides a computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein 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 invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the offshore wind farm impedance equivalent modeling method.

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

[0055] Figure 1 A schematic flow chart of a method for analyzing resonance stability of an offshore wind power grid-connected system maintaining a resonance mode according to the present invention;

[0056] Figure 2 A diagram showing the structure of a resonant stability analysis system for an offshore wind power grid-connected system that maintains a resonant mode according to the present invention;

[0057] Figure 3 A schematic diagram of the structure of an offshore wind power grid-connected system analyzed in an application example of the present invention;

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

[0059] Figure 5 This is a schematic diagram of an equivalent circuit in the s-domain of an offshore wind power grid-connected system analyzed in an application example of the present invention after the impedance of a target offshore wind farm is equivalent;

[0060] Figure 6 A schematic diagram of a logical structure of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0061] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0062] Example 1

[0063] like Figure 1 As shown, the present invention provides a method for analyzing the resonance stability of an offshore wind power grid-connected system maintaining a resonance mode, which comprises the following steps:

[0064] (1) Establish the s-domain impedance model of each electrical equipment in the offshore wind farm in the offshore wind power grid-connected system, 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.

[0065] The test signal method can be used to establish the s-domain impedance model of the wind turbine. The specific steps are as follows: after the wind turbine enters the steady-state operation state, a sinusoidal disturbance voltage signal of a certain frequency in the frequency band of interest is applied at the wind turbine grid connection point for 1 second. The amplitude of the signal is not greater than 5% of the voltage amplitude of the wind turbine grid connection point under the steady-state operation state. At the same time, the current signal of the wind turbine grid connection point during this time is recorded. The steady-state current of the wind turbine grid connection point in the same time before the sinusoidal disturbance voltage signal is applied is subtracted from the current signal, and the sinusoidal disturbance voltage signal is finally obtained. The disturbance current signal of the wind turbine generator set under the excitation of the signal; the time domain data of the sinusoidal disturbance voltage signal and the disturbance current signal are converted into frequency domain data through FFT analysis, and 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 generator set at this frequency; discrete frequency points are taken at a certain step size in the frequency band of interest, and the above method is repeated at each frequency point; the frequency domain impedance model of the wind turbine generator set in the frequency band of interest is obtained through data fitting, and then the s-domain impedance model of the wind turbine generator set 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] Where: f 0 is the fundamental frequency; X 0 is the leakage reactance of the transformer at the fundamental frequency; S N is the rated capacity of the transformer.

[0069] The specific steps for establishing the cable S-domain impedance model are as follows: calculate the impedance parameters per unit length, consider the frequency-varying characteristics of the parameters, and construct a full-dimensional series impedance matrix according to the geometric parameters. The full-dimensional series impedance matrix is ​​transformed into different three-phase series impedance matrices according to different cable grounding methods. The three-phase series impedance matrix obtains a sequence impedance matrix through sequence transformation, and only considers the positive-sequence impedance per unit length. Repeat the above calculation process at each frequency point in the frequency band of interest; calculate the admittance parameters per unit length, ignore the frequency-varying characteristics of the parameters and the line conductance, and calculate the capacitance per unit length according to the geometric parameters; calculate the entire 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 an S-domain expression to obtain the cable S-domain impedance model.

[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 then 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 model of each electrical equipment in the target offshore wind farm needs to be converted 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.

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

[0072] The nodes of the s-domain equivalent circuit of the target offshore wind farm 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;

[0073] The main diagonal elements in the s-domain node admittance matrix represent the self-admittance value of the corresponding node, and the remaining elements represent the mutual admittance value 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 s-domain impedance is Z 1 When the element is connected to the i node, its influence on the target offshore wind farm s domain node admittance matrix is ​​to make Y ii Add 1 / Z 1 ; When an s-domain impedance is Z 2 When the element is connected between the j node and the k node, its influence on the node admittance matrix of the target offshore wind farm s domain is to make Y jj and Y kk Add 1 / Z 2 , while making Y jk and Y kj Add (-1 / Z 2 ); the form of the target offshore wind farm s domain node admittance matrix is:

[0074]

[0075] The s-domain node admittance matrix of the target offshore wind farm is divided into the following blocks:

[0076]

[0077] Where: Y 0 (s) is the s-domain branch admittance vector between the common connection point and other nodes in the target offshore wind farm; is the admittance matrix of the target offshore wind farm s domain nodes except the public connection point.

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

[0079] The current i is injected only at the target offshore wind farm common connection point 0 (s);

[0080] Establish the node voltage equation of the target offshore wind farm:

[0081]

[0082] Where: v(s) is the voltage vector of the s-domain node of the target offshore wind farm; i(s) is the injected current vector of the s-domain node of the target offshore wind farm;

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

[0084]

[0085] Where: v'(s) is the voltage vector of the s-domain nodes of the target offshore wind farm except the common connection point;

[0086] Obtain the node voltage v of the common connection point of the target offshore wind farm 0 (s) is:

[0087]

[0088] S-domain equivalent impedance of the target offshore wind farm for:

[0089]

[0090] (4) The s-domain impedance model of each electrical device in the offshore wind power grid-connected system, except for the offshore wind farm, is converted 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 converted 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. According to the topological structure of the offshore wind power grid-connected system, its s-domain equivalent circuit is constructed, and then its s-domain node admittance matrix is ​​obtained.

[0091] (5) All zeros of the determinant of the s-domain node admittance matrix of the offshore wind power grid-connected system are calculated within the frequency band of interest. The zero point calculation is based on the decoupling characteristics of the real and imaginary parts of the zero points corresponding to resistance and reactance, respectively, and is mainly divided into the following two stages:

[0092] 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 an s-domain node susceptance matrix. The zeros of the s-domain node susceptance matrix determinant are real numbers and close to the imaginary part of the zeros of the s-domain node admittance matrix determinant. The zeros of the s-domain node susceptance matrix determinant within the frequency band of interest are calculated, thereby determining the number of zeros of the s-domain node admittance matrix determinant within the frequency band of interest, and further determining the node voltage vibration mode to obtain the best controllable and observable node;

[0093] Phase 2: In the complete system considering all component resistances, the zeros of the determinant of the s-domain node admittance matrix are accurately calculated using the test signal method at the best controllable and observable nodes.

[0094] (6) Analyze the resonant stability of the offshore wind power grid-connected system based on the zero-point characteristics and the optimal controllable and observable node positions.

[0095] According to the position of the best controllable and observable node, it is judged 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 resonant 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 some resonant modes 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 resonant mode of the offshore wind power system.

[0096] For the zero point that characterizes the resonant mode of the offshore wind power system, its real part represents the attenuation characteristics of the resonant mode. When the real part is positive, the resonant mode is a divergent unstable resonant mode; when the real part is negative, the resonant mode is an attenuated stable resonant mode; the imaginary part of the zero point represents the resonant angular frequency of the resonant mode; when all resonant modes of the offshore wind power grid-connected system are stable resonant modes, the offshore wind power grid-connected system is stable within the frequency band of interest, otherwise there is a resonance risk and resonance suppression is required.

[0097] Example 2

[0098] This embodiment provides a resonant stability analysis system for an offshore wind power grid-connected system maintaining a resonant mode, such as Figure 2 As shown, it consists of an impedance model building unit, an offshore wind farm S-domain node admittance matrix building unit, an offshore wind farm S-domain equivalent impedance acquisition unit, an offshore wind power grid-connected system S-domain node admittance matrix acquisition unit, a zero point and optimal controllable and observable node calculation unit and a resonance stability analysis unit.

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

[0100] In the impedance model building unit, the wind turbine s-domain impedance model building can use the test signal method, and the specific steps are as follows: after the wind turbine enters the steady-state operation state, a sinusoidal disturbance voltage signal of a certain frequency in the frequency band of interest is applied at the wind turbine grid connection point for a duration of 1 second, and the amplitude of the signal is not greater than 5% of the voltage amplitude of the wind turbine grid connection point in the steady-state operation state. At the same time, the current signal of the wind turbine grid connection point during this time is recorded, and the steady-state current of the wind turbine grid connection point in the same time before the sinusoidal disturbance voltage signal is applied is subtracted from the current signal, and finally the positive The disturbance current signal of the wind turbine generator set under the excitation of the sinusoidal disturbance voltage signal; the time domain data of the sinusoidal disturbance voltage signal and the disturbance current signal are converted into frequency domain data through FFT analysis, and 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 generator set at this frequency; discrete frequency points are taken at a certain step size in the frequency band of interest, and the above method is repeated at each frequency point; the frequency domain impedance model of the wind turbine generator set in the frequency band of interest is obtained through data fitting, and then the s-domain impedance model of the wind turbine generator set in the frequency band of interest 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] Where: f 0 is the fundamental frequency; X 0 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 cable S-domain impedance model are as follows: calculate the impedance parameters per unit length, consider the frequency-varying characteristics of the parameters, and construct a full-dimensional series impedance matrix according to the geometric parameters. The full-dimensional series impedance matrix is ​​transformed into different three-phase series impedance matrices according to different cable grounding methods. The three-phase series impedance matrix obtains a sequence impedance matrix through sequence transformation, and only considers the positive sequence impedance per unit length. Repeat the above calculation process at each frequency point in the frequency band of interest; calculate the admittance parameters per unit length, ignore the frequency-varying characteristics of the parameters and the line conductance, and calculate the capacitance per unit length according to the geometric parameters; calculate the entire 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 an S-domain expression, and obtain the cable S-domain impedance model.

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

[0106] 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 converted to the basic voltage level. The basic voltage level is generally selected as the voltage level of the submarine cables in the target offshore wind farm.

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

[0108] The nodes of the s-domain equivalent circuit of the target offshore wind farm 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;

[0109] The main diagonal elements in the s-domain node admittance matrix represent the self-admittance value of the corresponding node, and the remaining elements represent the mutual admittance value 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 s-domain impedance is Z 1 When the element is connected to the i node, its influence on the target offshore wind farm s domain node admittance matrix is ​​to make Y ii Add 1 / Z 1 ; When an s-domain impedance is Z 2 When the element is connected between the j node and the k node, its influence on the node admittance matrix of the target offshore wind farm s domain is to make Y jj and Y kk Add 1 / Z 2 , while making Y jk and Y kj Add (-1 / Z 2 ); the form of the target offshore wind farm s domain node admittance matrix is:

[0110]

[0111] The s-domain node admittance matrix of the target offshore wind farm is divided into the following blocks:

[0112]

[0113] Where: Y 0 (s) is the s-domain branch admittance vector between the common connection point and other nodes in the target offshore wind farm; is the admittance matrix of the target offshore wind farm s domain nodes except the public connection point.

[0114] (3) Offshore wind farm S-domain equivalent impedance acquisition unit: inject current into the common connection point of the target offshore wind farm, calculate the node voltage of the common connection 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 common connection point.

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

[0116] The current i is injected only at the target offshore wind farm common connection point 0 (s);

[0117] Establish the node voltage equation of the target offshore wind farm:

[0118]

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

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

[0121]

[0122] Where: v'(s) is the voltage vector of the s-domain nodes of the target offshore wind farm except the common connection point;

[0123] Obtain the node voltage v of the common connection point of the target offshore wind farm 0 (s) is:

[0124]

[0125] S-domain equivalent impedance of the target offshore wind farm for:

[0126]

[0127] (4) Offshore wind power grid-connected system S-domain node admittance matrix construction unit: The offshore wind power grid-connected system S-domain equivalent circuit 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 establishing the S-domain equivalent circuit of the offshore wind power grid-connected system, the S-domain impedance model of each electrical equipment in the offshore wind power grid-connected system except the offshore wind farm needs to be converted 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 converted 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) Zero point and optimal controllable and observable node calculation unit: Calculate all zero points and the corresponding optimal controllable and observable nodes of the determinant of the s-domain node admittance matrix of the offshore wind power grid-connected system within the frequency band of interest.

[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 and imaginary parts of the zero point corresponding to the resistance and reactance respectively, and is mainly divided into the following two stages;

[0131] 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 an s-domain node susceptance matrix. The zeros of the s-domain node susceptance matrix determinant are real numbers and close to the imaginary part of the zeros of the s-domain node admittance matrix determinant. The zeros of the s-domain node susceptance matrix determinant within the frequency band of interest are calculated, thereby determining the number of zeros of the s-domain node admittance matrix determinant within the frequency band of interest, and further determining the node voltage vibration mode to obtain the best controllable and observable node;

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

[0133] (6) Resonance stability analysis unit: Analyze the resonance stability of the offshore wind power grid-connected system based on the zero-point characteristics and the optimal controllable and observable node positions.

[0134] According to the position of the best controllable and observable node, it is judged 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 resonant 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 some resonant modes 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 resonant mode of the offshore wind power system.

[0135] It can characterize the zero point of the resonant mode of the offshore wind power system. Its real part represents the attenuation characteristics of the resonant mode. When the real part is positive, the resonant mode is a divergent unstable resonant mode; when the real part is negative, the resonant mode is an attenuated stable resonant mode; the imaginary part of the zero point represents the resonant angular frequency of the resonant mode; when all resonant modes of the offshore wind power grid-connected system are stable resonant modes, the offshore wind power grid-connected system is stable within the frequency band of interest, otherwise there is a resonance risk and resonance suppression is required.

[0136] Application Examples

[0137] The following is an example of an offshore wind power grid-connected system. Figure 3 As shown, an impedance equivalent model is performed on the offshore wind farm it contains, and the resonant stability of the offshore wind power grid-connected system is analyzed.

[0138] The s-domain impedance model of each electrical equipment in the offshore wind farm in the offshore wind power grid-connected system is established, 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. Among them, the wind turbine specifically includes the double-fed wind turbine and the direct-drive wind turbine, and the s-domain impedance model of the wind turbine is established by the test signal method; the transformer specifically includes the step-up transformer at the outlet of the wind turbine and the offshore step-up transformer at the busbar, and the transformer s-domain impedance model is established according to the fundamental frequency parameters; the cable specifically includes three-core cable, single-core submarine cable and single-core onshore cable, and the cable s-domain impedance model based on the accurate π model is established considering the frequency-varying characteristics and distribution characteristics of the parameters.

[0139] The s-domain impedance models of all electrical equipment in the target offshore wind farm are converted to the basic voltage level. The basic voltage level is generally selected as the voltage level of the submarine cables in the target offshore wind farm. According to the topological structure of the target offshore wind farm, its s-domain equivalent circuit is constructed, such as Figure 4 As shown, the nodes of the s-domain equivalent circuit of the target offshore wind farm are renumbered to obtain its s-domain node admittance matrix, and its s-domain node admittance matrix is ​​divided into blocks.

[0140] Current is injected into the common connection point of the target offshore wind farm, the node voltage equation of the target offshore wind farm is established, and the node voltage of the common connection point of the target offshore wind farm is calculated by transforming the node voltage equation, thereby obtaining the S-domain equivalent impedance of the target offshore wind farm.

[0141] The s-domain impedance model of each electrical device in the offshore wind power grid-connected system except the offshore wind farm is converted 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. According to the topological structure of the offshore wind power grid-connected system, its s-domain equivalent circuit is constructed, such as Figure 5 As shown, the s-domain node admittance matrix is ​​obtained.

[0142] All zeros of the determinant of the s-domain node admittance matrix of the offshore wind power grid-connected system are calculated in the frequency band of interest of 20-2500 Hz under the following three conditions: before the target offshore wind farm impedance is equivalent, after the target offshore wind farm adopts the new impedance equivalent based on the s-domain node admittance matrix transformation introduced in the present invention, and after the target offshore wind farm adopts the traditional impedance equivalent of series-parallel and star-delta changes. The zero point solution is based on the decoupling characteristics of the real and imaginary parts of the zero point corresponding to the resistance and reactance respectively, which is mainly divided into estimating the imaginary part of the zero point in the undamped system and calculating the zero point in the complete system.

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

[0144] Table 1

[0145]

[0146] There are two zeros in the determinant of the s-domain node admittance matrix of the offshore wind power grid-connected system. The value of zero point 1 before and after impedance equivalence is basically unchanged, and the best controllable and observable node of zero point 1 after impedance equivalence is located outside the target offshore wind farm. Therefore, zero point 1 after impedance equivalence can characterize the resonant mode of the offshore wind power system; the value of zero point 2 before and after impedance equivalence is quite different, and the best controllable and observable node of zero point 2 after impedance equivalence is the common connection point of the target offshore wind farm. Therefore, zero point 2 after impedance equivalence cannot characterize the resonant mode of the offshore wind power system. In addition, the zero point calculation results of the new impedance equivalence based on s-domain node admittance matrix transformation introduced in the present invention and the traditional impedance equivalence using series-parallel and star-delta changes are the same, which proves the effectiveness of the method introduced in the present invention. For zero point 1 that characterizes the resonant mode of the offshore wind power system after impedance equivalence, its actual part is negative, and the resonant mode represented is a stable resonant mode of attenuation.

[0147] Example 3

[0148] This embodiment provides an electronic device, comprising: at least one processor; and a memory connected to the at least one processor in communication. The memory stores a computer program executable by the at least one processor, and when the computer program is executed by the at least one processor, the electronic device executes the method according to Embodiment 1 of the present invention.

[0149] Example 4

[0150] This 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 used to cause the computer to execute the method according to Embodiment 1 of the present invention.

[0151] refer to Figure 6 , a block diagram of an electronic device 400 that can be used as a server or client of the present invention will now be described, which is an example of a hardware device that can be applied to various aspects of the present invention. The electronic device is intended to represent various forms of digital electronic computer devices, such as laptop computers, desktop computers, workbenches, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device can also represent various forms 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 merely examples and are not intended to limit the implementation of the present invention described and / or required herein.

[0152] like Figure 6As shown, the electronic device 400 includes a computing unit 401, which can perform various appropriate actions and processes according to a computer program stored in a read-only memory (ROM) 402 or a computer program loaded from a storage unit 408 into a random access memory (RAM) 403. 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 via 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, a storage unit 408, and a communication unit 409. The input unit 406 may be any type of device capable of inputting information to the electronic device 400, and the input unit 406 may receive input digital or character information, and generate key signal inputs related to user settings and / or function control of the electronic device. The output unit 407 may be any type of device capable of presenting information, and may 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 may include, but is not limited to, a disk, an optical disk. The communication unit 409 allows the electronic device 400 to exchange information / data with other devices via a computer network such as the Internet and / or various telecommunication networks, and may 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 may be a variety of general and / or special processing components with 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 dedicated artificial intelligence (AI) computing chips, various computing units running machine learning model algorithms, digital signal processors (DSPs), and any appropriate processors, controllers, microcontrollers, etc. The computing unit 401 performs the various methods and processes described above. For example, in some embodiments, the aforementioned metal corrosion prediction method may be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as a storage unit 408. In some embodiments, part or all of the computer program may be loaded and / or installed on the electronic device 400 via the ROM 402 and / or the communication unit 409. In some embodiments, the computing unit 401 may be configured to perform the aforementioned metal corrosion prediction method in any other appropriate manner (e.g., by means of firmware).

[0155] The program code for implementing the method of the present invention can be written in any combination of one or more programming languages. These program codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer or other programmable data processing device, so that the program code, when executed by the processor or controller, enables the functions / operations specified in the flow chart and / or block diagram to be implemented. The program code can be executed entirely on the machine, partially on the machine, partially on the machine as a stand-alone software package and partially on a remote machine, or entirely on a remote machine or server.

[0156] In the context of the present invention, a machine-readable medium may be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, device, or equipment. A machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or equipment, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, 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 disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0157] As used herein, the terms "machine-readable medium" and "computer-readable medium" refer to any computer program product, apparatus, and / or device (e.g., disk, optical disk, memory, programmable logic device (PLD)) for providing 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 for providing machine instructions and / or data to a programmable processor.

[0158] To provide interaction with a user, the systems and techniques described herein 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 pointing device (e.g., a mouse or trackball) through which the user can provide input to the computer. Other types of devices can also be used to provide interaction with the user; for example, the 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 input, voice input, or tactile input).

[0159] The systems and techniques described herein may be implemented in a computing system that includes back-end components (e.g., as a data server), or a computing system that includes middleware components (e.g., an application server), or a computing system that includes front-end components (e.g., a user computer with a graphical user interface or a web browser through which a user can interact with implementations of the systems and techniques described herein), or a computing system that includes any combination of such back-end components, middleware components, or front-end components. The components of the system may 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] A computer system may include clients and servers. Clients and servers are generally remote from each other and usually interact through a communication network. The relationship of client and server is generated by computer programs running on respective computers and having a client-server relationship to each other.

[0161] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those familiar with the art can easily make various modifications to the above embodiments and apply the general principles described herein to other cases without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made to the present invention by those skilled in the art based on the disclosure of the present invention should be within the scope of protection of the present invention.

Claims

1. A resonance stability analysis method for an offshore wind power grid-connected system, characterized in that: Includes steps: Establish the s-domain impedance model of each electrical equipment in the offshore wind farm in the offshore wind power grid-connected system, including the s-domain impedance model of the wind turbine, the s-domain impedance model of the transformer and the s-domain impedance model of the cable; According to the topological structure of the target offshore wind farm and the s-domain impedance model of each electrical equipment in the target offshore wind farm, the s-domain equivalent circuit of the target offshore wind farm is constructed, and then the s-domain node admittance matrix of the target offshore wind farm is obtained; Injecting current into the common connection point of the target offshore wind farm, calculating the node voltage of the common connection point of the target offshore wind farm, and obtaining the s-domain equivalent impedance of the target offshore wind farm according to the injected current, node voltage and s-domain node admittance matrix of the target offshore wind farm at the common connection point; 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, the s-domain equivalent circuit of the offshore wind power grid-connected system is constructed, and then the s-domain node admittance matrix of the offshore wind farm grid-connected system is obtained; Calculate all 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 within the frequency band of interest; The resonant stability of offshore wind power grid-connected systems is analyzed based on zero-point characteristics and optimal controllable and observable node locations.

2. The method according to claim 1, characterized in that The wind turbine s-domain impedance model is established using a test signal method, and the specific steps are as follows: after the wind turbine enters a steady-state operation state, a sinusoidal disturbance voltage signal of a certain frequency in a frequency band of interest is applied at the wind turbine grid connection point for a duration of 1 second, and the amplitude of the signal is not greater than 5% of the voltage amplitude of the wind turbine grid connection point under the steady-state operation state, and the current signal of the wind turbine grid connection point during this time is recorded, and 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 the current signal, 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 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 this frequency. Discrete frequency points are taken at a certain step size in the frequency band of interest, 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 through 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.

3. The method according to claim 1, characterized in that The steps of establishing the cable s-domain impedance model are as follows: calculating the impedance parameters per unit length, considering the frequency-varying characteristics of the parameters, constructing a full-dimensional series impedance matrix according to the geometric parameters, transforming the full-dimensional series impedance matrix into different three-phase series impedance matrices according to different grounding methods of the cable, and obtaining a sequence impedance matrix through sequence transformation of the three-phase series impedance matrix, considering only the positive sequence impedance per unit length, and repeating the above calculation process at each frequency point in the frequency band of interest; calculating the admittance parameters per unit length, ignoring the frequency-varying characteristics of the parameters and the line conductance, and calculating the capacitance per unit length according to the geometric parameters; The parameters of the entire line are calculated, and the distribution characteristics of the parameters are considered to establish an accurate π model. The resistance, inductance and capacitance in the accurate π model are converted 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 target offshore wind farm s-domain node admittance matrix are as follows: The nodes of the s-domain equivalent circuit of the target offshore wind farm 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; 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 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 s-domain impedance Z1 is connected to node i, its influence 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 s-domain impedance Z2 is connected between nodes j and k, its impact 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 make Y jk and Y kj Add (-1 / Z2); the form of the target offshore wind farm s domain node admittance matrix is: The s-domain node admittance matrix of the target offshore wind farm is divided into the following blocks: Where: Y0(s) is the s-domain branch admittance vector between the common connection point and other nodes in the target offshore wind farm; is the admittance matrix of the target offshore wind farm s domain nodes except the public connection point.

5. The method according to claim 4, characterized in that The specific calculation steps of the s-domain equivalent impedance of the target offshore wind farm are as follows: The current i0(s) is injected only at the public connection point of the target offshore wind farm; Establish the node voltage equation of the target offshore wind farm: Where: v(s) is the voltage vector of the s-domain node of the target offshore wind farm; i(s) is the injected current vector of the s-domain node of the target offshore wind farm; The node voltage equation of the target offshore wind farm is transformed into: Where: v'(s) is the voltage vector of the s-domain nodes of the target offshore wind farm except the common connection point; The node voltage v0(s) of the common connection point of the target offshore wind farm is obtained as: 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 the offshore wind power grid-connected system is based on the decoupling characteristics of the real and imaginary parts of the zero point corresponding to 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 an s-domain node susceptance matrix. The zeros of the s-domain node susceptance matrix determinant are real numbers and close to the imaginary part of the zeros of the s-domain node admittance matrix determinant. The zeros of the s-domain node susceptance matrix determinant within the frequency band of interest are calculated, thereby determining the number of zeros of the s-domain node admittance matrix determinant within the frequency band of interest, and further determining the node voltage vibration mode to obtain the best controllable and observable node; Phase 2: In the complete system considering all component resistances, the zeros of the determinant of the s-domain node admittance matrix are accurately calculated using the test signal method at the best controllable and observable nodes.

7. The method according to claim 1, characterized in that According to the position of the best controllable and observable node, it is judged 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 resonant 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 some resonant modes 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 resonant mode 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 building unit: used to build the s-domain impedance model of each electrical equipment in the offshore wind farm in the offshore wind power grid-connected system, including the s-domain impedance model of the wind turbine, the s-domain impedance model of the transformer and the s-domain impedance model of the cable; Offshore wind farm s-domain node admittance matrix construction unit: constructs the target offshore wind farm s-domain equivalent circuit according to the topological structure of the target offshore wind farm and the s-domain impedance model of each electrical equipment in the target offshore wind farm, and then obtains the target offshore wind farm s-domain node admittance matrix; Offshore wind farm s-domain equivalent impedance acquisition unit: inject current into the common connection point of the target offshore wind farm, calculate the node voltage of the common connection point of the target offshore wind farm, and obtain the s-domain equivalent impedance of the target offshore wind farm according to the injected current, node voltage and s-domain node admittance matrix of the target offshore wind farm at the common connection point; Offshore wind power grid-connected system s-domain node admittance matrix acquisition unit: constructs an offshore wind power grid-connected system s-domain equivalent circuit 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 obtains the offshore wind power grid-connected system s-domain node admittance matrix; Zero point and best controllable and observable node calculation unit: calculate 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 within the frequency band of interest; Resonance stability analysis unit: Analyze the resonance stability of offshore wind power grid-connected systems based on zero-point characteristics and optimal controllable and observable node positions.

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, the steps of the method according to any one of claims 1 to 7 are implemented.

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

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