Method and system for evaluating stability of power transmission system through fan control strategy

Abstract

The invention provides a method and system for evaluating the stability of a power transmission system through a fan control strategy, and the method comprises the steps: building an impedance model of a fan under the network-following type control and network-constructing type control through a harmonic domain modeling method based on the simulation data of the fan connected to the power transmission system, the simulation data comprises topological structure parameters and controller parameters of the fan; performing simulation analysis on the impedance model of the fan under the following network type control and the construction network type control to obtain a dynamic response curve of the fluctuation amplitude of the operation data of the fan along with the time change under the following network type control and the construction network type control; performing spectral analysis on the dynamic response curve to obtain simulation harmonic suppression results of the fan under the following network type control and the construction network type control; based on the simulation harmonic suppression result, the influence of the fan on the stability of the power transmission system under the following network type control and the construction network type control is evaluated, and the influence of the fan on the stability of the power transmission system under the following network type control and the construction network type control can be accurately evaluated.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric power systems, and in particular relates to a method and system for evaluating the stability of a power transmission system using a wind turbine control strategy. Background Art

[0002] In the application scenario of grid-connected flexible direct current (FDC) for new energy, when the grid-connected wind turbine and the grid-connected wind turbine are connected to the system, there are technical difficulties in stability analysis. The traditional impedance modeling method is difficult to take into account both the actual application of the project and the accuracy of the modeling, resulting in a deviation between the stability analysis results and the actual situation.

[0003] The existing wind turbine grid-following and grid-forming control impedance models are still imperfect and cannot accurately determine the impact of wind turbines on the stability of the transmission system under grid-following control and grid-forming control. Summary of the invention

[0004] In order to overcome the above-mentioned deficiencies of the prior art, in a first aspect, the present invention proposes a method for evaluating the stability of a power transmission system using a wind turbine control strategy, comprising:

[0005] Based on the simulation data of the wind turbine connected to the power transmission system, the impedance model of the wind turbine under the grid-following control and the grid-forming control is established by using the harmonic domain modeling method, wherein the simulation data includes the topological structure parameters and the controller parameters of the wind turbine;

[0006] Simulating and analyzing the impedance model of the wind turbine under the grid-following control and the grid-forming control, and obtaining a dynamic response curve of the fluctuation amplitude of the operation data of the wind turbine over time under the grid-following control and the grid-forming control;

[0007] Performing spectrum analysis on the dynamic response curve to obtain simulated harmonic suppression results of the wind turbine under grid-following control and grid-forming control;

[0008] Based on the simulation harmonic suppression results, the impact of the wind turbine on the stability of the power transmission system under grid-following control and grid-forming control is evaluated.

[0009] Preferably, the impedance model of the wind turbine under the grid-following control and the grid-forming control is simulated and analyzed to obtain a dynamic response curve of the fluctuation amplitude of the operation data of the wind turbine under the grid-following control and the grid-forming control over time, including:

[0010] Based on the impedance model of the wind turbine under the grid-following control and the grid-building control, a simulation circuit of the flexible direct current transmission system for the wind farm grid connection is constructed by using simulation software;

[0011] Setting the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller in the flexible DC power transmission system simulation circuit;

[0012] The set flexible direct current transmission system simulation circuit is processed by a small signal analysis method to obtain a dynamic response curve of the fluctuation amplitude of the operation data of the wind turbine changing with time under the grid-following control and the grid-forming control.

[0013] Preferably, the performing spectrum analysis on the dynamic response curve to obtain the simulated harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control includes:

[0014] Extracting the magnitude, variation trend and frequency distribution range of the fluctuation amplitude from the dynamic response curve;

[0015] Based on the magnitude of the fluctuation amplitude, the variation trend and the frequency distribution range, analyzing the relationship between the fluctuation amplitude and the frequency;

[0016] Based on the relationship between the fluctuation amplitude and the frequency, determining the frequency domain characteristics of the fluctuation amplitude;

[0017] Based on the frequency domain characteristics of the fluctuation amplitude, the dynamic response curve is subjected to spectrum analysis to obtain the simulated harmonic suppression results of the wind turbine under grid-following control and grid-forming control.

[0018] Preferably, the evaluating the influence of the wind turbine on the stability of the power transmission system under the grid-following control and the grid-forming control based on the simulation harmonic suppression result includes:

[0019] Based on the simulated harmonic suppression result, calculating the amplitude and phase angle of each harmonic component in the dynamic response curve;

[0020] Based on the amplitude and phase angle of each harmonic component, obtaining a total harmonic distortion value of the dynamic response curve;

[0021] Based on the total harmonic distortion value, determining the source of harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component;

[0022] Based on the sources of harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component, determining the relationship between the harmonic amplitude and the impedance of the wind turbine, and the correlation between the harmonic distortion and the control strategy;

[0023] Based on the relationship between the harmonic amplitude and the impedance of the wind turbine, and the correlation between the harmonic distortion and the control strategy, the impact of the wind turbine on the stability of the power transmission system under grid-following control and grid-forming control is evaluated.

[0024] Preferably, after calculating the amplitude and phase angle of each harmonic component in the dynamic response curve based on the simulated harmonic suppression result, the method further includes:

[0025] Based on the amplitude and phase angle of each harmonic component in the dynamic response curve, a damping ratio calculation method is used to calculate the damping ratio of the fan in two control modes: a grid-following type and a grid-forming type;

[0026] Based on the damping ratio of the wind turbine in the two control modes of following the grid and forming the grid, the ability of the wind turbine to reduce the oscillation risk in the two control modes of following the grid and forming the grid is determined.

[0027] Preferably, after performing small signal analysis on the configured flexible DC power transmission system simulation circuit to obtain a dynamic response curve of the fluctuation amplitude of the wind turbine operation data changing with time under the grid-following control and the grid-forming control, the method further includes:

[0028] In the flexible direct current transmission system simulation circuit, the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller are changed to determine the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the transmission system;

[0029] Based on the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the power transmission system, the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller and the integral coefficient of the controller when suppressing harmonics is determined.

[0030] Preferably, after determining the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller when suppressing harmonics based on the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the power transmission system, the method further includes:

[0031] Applying the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller to an actual power transmission system, and obtaining actual measured data of the wind turbine in the actual power transmission system;

[0032] Based on the measured data of the wind turbine, determining the measured harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control;

[0033] Based on the simulated harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control and the measured harmonic suppression results, the accuracy of the impedance model of the wind turbine under the grid-following control and the grid-forming control is verified.

[0034] Preferably, the topological structure parameters of the wind turbine include: the number of submodules of the topological structure, the capacitance value of the topological structure, and the inductance value of the reactor of the topological structure;

[0035] The control system parameters of the fan include: a proportional coefficient and an integral coefficient of a controller in the control system.

[0036] Preferably, the impedance model of the wind turbine under grid-following control and grid-forming control is established by using a harmonic domain modeling method based on the simulation data of the wind turbine connected to the power transmission system, including:

[0037] Based on the topological structure parameters and controller parameters of the wind turbine connected to the transmission system, the harmonic domain modeling method is used to establish the impedance model of the wind turbine under grid-following control and grid-forming control for the AC current loop, DC voltage loop and circulating current suppression loop of the wind turbine in the topological structure.

[0038] In a second aspect, the present invention also proposes a system for evaluating the stability of a power transmission system using a wind turbine control strategy, comprising:

[0039] A model building module, for establishing an impedance model of a wind turbine connected to a power transmission system using a harmonic domain modeling method under grid-following control and grid-forming control based on simulation data of the wind turbine connected to a power transmission system, wherein the simulation data includes topological structure parameters and controller parameters of the wind turbine;

[0040] A dynamic response curve acquisition module is used to simulate and analyze the impedance model of the wind turbine under the grid-following control and the grid-forming control, and to obtain a dynamic response curve of the fluctuation amplitude of the operation data of the wind turbine over time under the grid-following control and the grid-forming control;

[0041] A simulation harmonic suppression result acquisition module is used to perform spectrum analysis on the dynamic response curve to obtain simulation harmonic suppression results of the wind turbine under grid-following control and grid-forming control;

[0042] The stability impact assessment module is used to assess the stability impact of the wind turbine on the power transmission system under grid-following control and grid-forming control based on the simulation harmonic suppression results.

[0043] Preferably, the dynamic response curve acquisition module includes:

[0044] A simulation circuit construction submodule is used to construct a simulation circuit of a flexible direct current transmission system for connecting a wind farm to the grid using simulation software based on an impedance model of the wind turbine under grid-following control and grid-forming control;

[0045] A simulation circuit setting submodule, used to set the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller in the simulation circuit of the flexible DC power transmission system;

[0046] The dynamic response curve acquisition submodule is used to perform small signal analysis on the flexible DC transmission system simulation circuit after setting, and obtain the dynamic response curve of the fluctuation amplitude of the wind turbine operation data changing with time under the grid-following control and the grid-forming control.

[0047] Preferably, the simulation harmonic suppression result acquisition module includes:

[0048] An extraction submodule, used for extracting the magnitude, change trend and frequency distribution range of the fluctuation amplitude from the dynamic response curve;

[0049] A relationship analysis submodule, used for analyzing the relationship between the fluctuation amplitude and the frequency based on the size of the fluctuation amplitude, the change trend and the frequency distribution range;

[0050] A frequency domain characteristic determination submodule, used to determine the frequency domain characteristic of the fluctuation amplitude based on the relationship between the fluctuation amplitude and the frequency;

[0051] The simulation harmonic suppression result acquisition submodule is used to perform spectrum analysis on the dynamic response curve based on the frequency domain characteristics of the fluctuation amplitude, and obtain the simulation harmonic suppression results of the wind turbine under grid-following control and grid-forming control.

[0052] Preferably, the stability impact assessment module includes:

[0053] An amplitude and phase angle calculation submodule, used to calculate the amplitude and phase angle of each harmonic component in the dynamic response curve based on the simulated harmonic suppression result;

[0054] A total harmonic distortion value acquisition submodule, used to acquire a total harmonic distortion value of the dynamic response curve based on the amplitude and phase angle of each harmonic component;

[0055] A harmonic determination submodule, used to determine the source of harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component based on the total harmonic distortion value;

[0056] A correlation determination submodule, for determining the relationship between the harmonic amplitude and the impedance of the wind turbine, and the correlation between the harmonic distortion and the control strategy based on the source of the harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component;

[0057] The stability impact assessment submodule is used to assess the impact of the wind turbine on the stability of the power transmission system under grid-following control and grid-forming control based on the relationship between the harmonic amplitude and the impedance of the wind turbine and the correlation between the harmonic distortion and the control strategy.

[0058] Preferably, the system further comprises:

[0059] A damping ratio calculation module, for calculating the damping ratio of the fan in two control modes, a grid-following type and a grid-forming type, by using a damping ratio calculation method based on the amplitude and phase angle of each harmonic component in the dynamic response curve;

[0060] The oscillation risk reduction capability determination module is used to determine the oscillation risk reduction capability of the wind turbine under the two control modes of following the grid and building the grid based on the damping ratio of the wind turbine under the two control modes of following the grid and building the grid.

[0061] Preferably, the system further comprises:

[0062] a relationship determination module, used to change the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller in the flexible DC power transmission system simulation circuit, and determine the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the power transmission system impedance;

[0063] The optimal combination determination module is used to determine the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller when suppressing harmonics based on the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the power transmission system.

[0064] Preferably, the system further comprises:

[0065] A measured data acquisition module, used to apply the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller to an actual power transmission system, and to acquire the measured data of the wind turbine in the actual power transmission system;

[0066] A measured harmonic suppression result acquisition module is used to determine the measured harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control based on the measured data of the wind turbine;

[0067] An accuracy verification module is used to verify the accuracy of the impedance model of the wind turbine under grid-following control and grid-forming control based on the simulated harmonic suppression results of the wind turbine under grid-following control and grid-forming control and the measured harmonic suppression results.

[0068] Preferably, the topological structure parameters of the wind turbine include: the number of submodules of the topological structure, the capacitance value of the topological structure, and the inductance value of the reactor of the topological structure;

[0069] The control system parameters of the fan include: a proportional coefficient and an integral coefficient of a controller in the control system.

[0070] Preferably, the model building module is specifically used to establish the impedance model of the wind turbine under grid-following control and grid-forming control by using the harmonic domain modeling method for the AC current loop, DC voltage loop and circulating current suppression loop of the wind turbine in the topology structure based on the topology parameters and controller parameters of the wind turbine connected to the power transmission system.

[0071] In a third aspect, the present invention application further proposes an electronic device, comprising: at least one processor and a memory; the memory and the processor are connected via a bus;

[0072] The memory is used to store one or more programs;

[0073] When the one or more programs are executed by the at least one processor, the method for evaluating the stability of a power transmission system using a wind turbine control strategy is implemented.

[0074] In a fourth aspect, the present invention application further proposes a readable storage medium having an execution program stored thereon, and when the execution program is executed, the method for evaluating the stability of a power transmission system by a wind turbine control strategy is implemented.

[0075] Compared with the closest prior art, the present invention has the following beneficial effects:

[0076] The present invention discloses a method and system for evaluating the stability of a power transmission system by a wind turbine control strategy, including: based on the simulation data of a wind turbine connected to the power transmission system, using the harmonic domain modeling method to establish an impedance model of the wind turbine under grid-following control and grid-forming control, wherein the simulation data includes the topological structure parameters and controller parameters of the wind turbine; simulating and analyzing the impedance model of the wind turbine under grid-following control and grid-forming control, and obtaining a dynamic response curve of the fluctuation amplitude of the operating data of the wind turbine under grid-following control and grid-forming control over time; performing spectrum analysis on the dynamic response curve to obtain the simulated harmonic suppression result of the wind turbine under grid-following control and grid-forming control; based on the simulated harmonic suppression result, evaluating the influence of the wind turbine under grid-following control and grid-forming control on the stability of the power transmission system. By establishing a perfect impedance model of the wind turbine under grid-following control and grid-forming control, and then simulating and analyzing the impedance model of the wind turbine under grid-following control and grid-forming control, the influence of the wind turbine on the stability of the power transmission system under grid-following control and grid-forming control can be accurately evaluated. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 A schematic flow chart of a method for evaluating the stability of a power transmission system using a wind turbine control strategy provided by the present invention;

[0078] Figure 2An architecture diagram of a system for evaluating the stability of a power transmission system using a wind turbine control strategy provided by the present invention;

[0079] Figure 3 The present invention application provides a circuit diagram of a flexible DC transmission system simulation circuit in a second specific use case of a method for evaluating the stability of a power transmission system using a wind turbine control strategy;

[0080] Figure 4 A schematic diagram of the operation of an electronic device provided in the present invention application. DETAILED DESCRIPTION

[0081] The specific implementation methods of the present invention are further described in detail below with reference to the accompanying drawings.

[0082] Embodiment 1:

[0083] like Figure 1 As shown, the present invention provides a method for evaluating the stability of a power transmission system using a wind turbine control strategy, comprising the following steps:

[0084] Step 1: Based on the simulation data of the wind turbine connected to the power transmission system, the impedance model of the wind turbine under the grid-following control and grid-forming control is established by using the harmonic domain modeling method, wherein the simulation data includes the topological structure parameters and controller parameters of the wind turbine;

[0085] Step 2: Simulate and analyze the impedance model of the wind turbine under the grid-following control and the grid-forming control to obtain a dynamic response curve of the fluctuation amplitude of the operation data of the wind turbine over time under the grid-following control and the grid-forming control;

[0086] Step 3: Performing spectrum analysis on the dynamic response curve to obtain simulation harmonic suppression results of the wind turbine under grid-following control and grid-forming control;

[0087] Step 4: Based on the simulation harmonic suppression results, evaluate the impact of the wind turbine on the stability of the power transmission system under grid-following control and grid-forming control.

[0088] In the above step 1, the topological structure parameters of the wind turbine may include: the number of submodules of the topological structure, the capacitance value of the topological structure, and the inductance value of the reactor of the topological structure;

[0089] The control system parameters of the fan may include: a proportional coefficient and an integral coefficient of a controller in the control system.

[0090] Secondly, based on the simulation data of the wind turbine connected to the power transmission system, the impedance model of the wind turbine under the grid-following control and the grid-forming control is established by using the harmonic domain modeling method, which may include:

[0091] Based on the topological structure parameters and controller parameters of the wind turbine connected to the transmission system, the harmonic domain modeling method is used to establish the impedance model of the wind turbine under grid-following control and grid-forming control for the AC current loop, DC voltage loop and circulating current suppression loop of the wind turbine in the topological structure.

[0092] In the above step 1, the simulation data of the wind turbine connected to the transmission system (for example, the transmission system of an offshore wind farm) is obtained; combined with the topological structure parameters and controller parameters of the wind turbine, the harmonic domain modeling method can be used to take into account the accuracy and engineering application feasibility of the modeling process, and a more complete impedance model of the wind turbine under grid-following control and grid-forming control is established. The main purpose is to combine the actual parameters of the wind turbine with the transmission system for impedance modeling, forming an impedance model of the wind turbine under grid-following control and grid-forming control, so as to facilitate the subsequent construction of a simulation circuit for the flexible DC transmission system connected to the wind farm and conduct simulation analysis.

[0093] In the above step 2: according to the impedance model of the wind turbine under the grid-following control and the grid-forming control established in step 1, PSCAD (Power Systems Computer Aided Design, electromagnetic transient simulation software) can be used to build a simulation circuit of the flexible DC transmission system for the wind farm grid connection, and then the dynamic response curves of the fluctuation amplitudes of the DC voltage, DC current, AC voltage, and AC current of the wind turbine under the two modes of grid-following control and grid-forming control over time can be obtained;

[0094] In the above step 2, the impedance model of the wind turbine under the grid-following control and the grid-forming control is simulated and analyzed to obtain the dynamic response curve of the fluctuation amplitude of the operation data of the wind turbine under the grid-following control and the grid-forming control over time, which may specifically include the following steps:

[0095] Step 2.1: Based on the impedance model of the wind turbine under the grid-following control and the grid-forming control, a simulation circuit of the flexible direct current transmission system for connecting the wind farm to the grid is constructed using simulation software;

[0096] Step 2.2: setting the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller in the simulation circuit of the flexible DC transmission system;

[0097] Step 2.3: Perform small signal analysis on the set flexible DC power transmission system simulation circuit to obtain a dynamic response curve of the fluctuation amplitude of the wind turbine's operating data changing with time under the grid-following control and the grid-forming control.

[0098] The simulation circuit of the flexible DC transmission system built in the above steps 2.1-2.3 should consider the main equipment including wind turbines, converters of the transmission system, transformers of the transmission system, DC transmission lines, etc. The simulation circuit of the flexible DC transmission system includes the main equipment including wind turbines, converters of the transmission system, transformers of the transmission system, DC transmission lines, etc. Set reasonable simulation parameters in the simulation circuit of the flexible DC transmission system. Among them, the simulation parameters include the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller, etc., to ensure that the simulation circuit can accurately reflect the characteristics of the actual system. Using the small signal analysis method, a small disturbance signal is introduced into the control system of the wind turbine. By analyzing the response characteristics of the control system, the dynamic characteristics of the wind turbine under grid-following control and grid-forming control are obtained. Grid-following control and grid-forming control are respectively adopted for the wind turbine. In the grid-following control, the control target of the wind turbine is to maintain a constant DC voltage, and in the grid-forming control, the control target of the wind turbine is to maintain a constant AC voltage and frequency. Through simulation calculation, the dynamic response curves of the fluctuation amplitude of DC voltage, DC current, AC voltage and AC current of the wind turbine under the two modes of grid-following control and grid-building control are obtained. The dynamic response characteristics of the wind turbine under the two control modes are compared and analyzed, and the impact of different control modes on system stability, power quality and other aspects is evaluated to provide a reference for practical engineering applications. According to the simulation analysis results, the control parameters of the wind turbine, such as the controller proportional coefficient, integral coefficient, etc., can also be optimized to improve the dynamic response performance and operation stability of the system, laying the foundation for the practical engineering application of the transmission system.

[0099] The above step 2.3, after performing small signal analysis on the set flexible DC power transmission system simulation circuit to obtain a dynamic response curve of the fluctuation amplitude of the wind turbine operation data changing with time under the grid-following control and the grid-forming control, may also include:

[0100] Step 2.3.1: In the flexible DC power transmission system simulation circuit, the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller are changed to determine the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the power transmission system;

[0101] Step 2.3.2: Based on the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the power transmission system, determine the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller and the integral coefficient of the controller when suppressing harmonics.

[0102] The above step 2.3.2, after determining the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller when suppressing harmonics based on the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the power transmission system, may further include:

[0103] Step a: applying the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller to an actual power transmission system, and obtaining actual measured data of the wind turbine in the actual power transmission system;

[0104] Step b: based on the measured data of the wind turbine, determining the measured harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control;

[0105] Step c: based on the simulated harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control and the measured harmonic suppression results, verify the accuracy of the impedance model of the wind turbine under the grid-following control and the grid-forming control.

[0106] In the above steps a, b and c, in the simulation circuit of the flexible DC transmission system. For example, the wind turbine can use a doubly-fed asynchronous generator with a rated power of 5MW and a rotor inertia range of 0.5 to 5s; the controller proportional coefficient range is 2 to 12, and the integral coefficient range is 10 to 50. Through simulation, the wind turbine impedance characteristic curve, harmonic distortion rate and system damping ratio under different parameter combinations are obtained. The K-means clustering algorithm is used to analyze the simulation results to determine the degree of influence of rotor inertia and controller parameters on the performance of the wind turbine system. Combining the clustering results and the power grid standards, two groups of optimal parameter combinations are determined: rotor inertia 5s, proportional coefficient 8, integral coefficient 30; rotor inertia 0.8s, proportional coefficient 10, integral coefficient 40. For the optimal parameter combination, further simulation verification is carried out in the PSCAD software. The results show that the selected optimal parameter combination can control the harmonic distortion rate within 3%, and increase the damping ratio to more than 5%, meeting the engineering requirements. Finally, the verified optimal parameter combination is used as a technical reference for the offshore wind power flexible DC transmission project to guide the actual engineering design and ensure the stable and reliable operation of the system.

[0107] The optimal parameter combination is used in the actual power transmission system, and the DC voltage control parameters of the actual power transmission system are set to ±320kV, the DC current control parameters are set to 5kA, the AC voltage control parameters are set to 220kV, and the AC current control parameters are set to 1kA. The data acquisition equipment is used to monitor the wind turbine control system in real time. For example, 1000 data points are collected per second to obtain the measured fluctuation data of the wind turbine under DC voltage, DC current, AC voltage and AC current. The obtained measured fluctuation data is cleaned to remove outliers and missing values, and then the maximum and minimum normalization method is used to normalize the data, and the data is mapped to the [0,1] interval to obtain standardized measured fluctuation data. Fast Fourier transform is used to perform spectrum analysis on the standardized measured fluctuation data, and the frequency resolution is set to 1Hz to obtain the spectrum analysis results of the measured data. The spectrum analysis results of the measured data are compared with those of the simulated data, and the amplitude error and phase error of the two at each frequency point are calculated. If the errors are within the preset threshold range of ±5%, the impedance model of the wind turbine under the grid-following control and grid-forming control is considered to be accurate; otherwise, it is necessary to optimize and improve the parameters of the impedance model of the wind turbine under the grid-following control and grid-forming control, such as adjusting the impedance value, optimizing the simulation circuit structure of the flexible DC transmission system, etc., until the error requirements are met. According to the optimized control parameters, the grid-forming control method is used to control the wind turbine control system. The control cycle can be set to 10ms to obtain the measured fluctuation data of DC voltage, DC current, AC voltage and AC current under grid-forming control.

[0108] The above-mentioned optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller is applied to the actual power transmission system, which can provide technical guidance for the actual power transmission system. At the same time, the measured harmonic suppression results of the wind turbine of DC voltage, DC current, AC voltage, and AC current are further used to verify the accuracy of the impedance model of the wind turbine under grid-following control and grid-forming control according to the simulated harmonic suppression results and the measured harmonic suppression results, which can effectively improve the accuracy of the impedance model of the wind turbine constructed by the present invention under grid-following control and grid-forming control.

[0109] In step 3: the short-time Fourier transform (STFT) method can be used to perform spectrum analysis on the fluctuation signal in the dynamic response curve obtained in step 2, and extract the time domain and frequency domain characteristic parameters of the fluctuation signal in the dynamic response curve. By performing frame processing on the fluctuation signal, for example, selecting each frame length as 1024 sampling points and the frame shift as 512 sampling points, using the Hamming window to perform window processing on each frame signal, and then performing Fourier transform on each frame signal, the time-frequency spectrum of the fluctuation signal is obtained. By analyzing the time-frequency spectrum, the magnitude, change trend and frequency distribution range of the fluctuation signal are obtained; the correlation law between the fluctuation amplitude and the frequency is studied by using the analysis method of the correlation between the magnitude, change trend and frequency distribution range of the fluctuation amplitude, and the frequency domain characteristics of the fluctuation amplitude can be determined by the correlation law between the fluctuation amplitude and the frequency; then, according to the frequency domain characteristics of the fluctuation amplitude, the spectrum analysis of the dynamic response curve is performed to obtain the simulation harmonic suppression results of the fan under the grid-following control and the grid-forming control.

[0110] In the above step 3, the frequency spectrum analysis of the dynamic response curve is performed to obtain the simulated harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control, which may specifically include the following steps:

[0111] Step 3.1: extracting the magnitude, change trend and frequency distribution range of the fluctuation amplitude from the dynamic response curve;

[0112] Step 3.2: Analyze the relationship between the fluctuation amplitude and the frequency based on the fluctuation amplitude, the change trend and the frequency distribution range;

[0113] Step 3.3: Based on the relationship between the fluctuation amplitude and the frequency, determine the frequency domain characteristics of the fluctuation amplitude;

[0114] Step 3.4: Based on the frequency domain characteristics of the fluctuation amplitude, the dynamic response curve is subjected to spectrum analysis to obtain the simulated harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control.

[0115] In the above step 3.1, according to the obtained dynamic response curve, short-time Fourier transform can be used to extract information such as the fluctuation amplitude, change trend and frequency distribution range, analyze the relationship between the fluctuation amplitude and frequency, judge the dominant component of the fluctuation frequency, determine the time domain of the fluctuation signal, and study the correlation between the fluctuation frequency and the control parameters of the wind turbine under grid-following control and grid-forming control, and the fluctuation amplitude and the impedance of the wind turbine under grid-following control and grid-forming control.

[0116] In the above step 3.2, the relationship between the fluctuation amplitude and the frequency is analyzed based on the acquired time domain parameters of the fluctuation signal, including the fluctuation amplitude, the change trend, the frequency distribution range, the dominant frequency component of the fluctuation signal, and the energy distribution of different frequency components.

[0117] In the above step 3.3, the correlation analysis method can be used to study the correlation between the fluctuation amplitude and frequency, establish a mathematical relationship model between the fluctuation amplitude and frequency, and quantify the correlation between the fluctuation amplitude and frequency. According to the changes in the control parameters of the wind turbine under the grid-following control and the grid-forming control, the influence of the control parameters on the fluctuation amplitude and frequency characteristics is analyzed, and the functional relationship between the control parameters and the fluctuation characteristics is established through the data fitting method. The system impedance data of the wind turbine under the grid-following control and the grid-forming control is obtained, and the impedance spectrum analysis technology is used to study the correlation between the impedance characteristics and the fluctuation amplitude and frequency, and reveal the frequency domain characteristics of the fluctuation amplitude.

[0118] In the above step 3.4, the results of time-frequency analysis, spectrum analysis, correlation analysis and other methods can be integrated to perform spectrum analysis on the dynamic response curve, revealing the internal connection between multiple factors such as fluctuation amplitude, frequency, control parameters, system impedance, etc. According to the internal connection between multiple factors, the fluctuation characteristics of the dynamic response curve of different control parameters of the wind turbine under grid-following control and grid-forming control are predicted, and the simulated harmonic suppression results of the wind turbine under grid-following control and grid-forming control are obtained. The simulated harmonic suppression results can provide a decision-making basis for optimizing wind turbine control strategies and improving power grid system performance.

[0119] In the above step 4, the evaluation of the influence of the wind turbine on the stability of the power transmission system under the grid-following control and the grid-forming control based on the simulation harmonic suppression result may include the following steps:

[0120] Step 4.1: Based on the simulated harmonic suppression result, the amplitude and phase angle of each harmonic component in the dynamic response curve are calculated;

[0121] Step 4.2: Based on the amplitude and phase angle of each harmonic component, obtain the total harmonic distortion value of the dynamic response curve;

[0122] Step 4.3: Based on the total harmonic distortion value, determine the source of harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component;

[0123] Step 4.4: Based on the source of the harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component, determine the relationship between the harmonic amplitude and the impedance of the wind turbine, and the correlation between the harmonic distortion and the control strategy;

[0124] Step 4.5: Based on the relationship between the harmonic amplitude and the impedance of the wind turbine, and the correlation between the harmonic distortion and the control strategy, evaluate the impact of the wind turbine on the stability of the power transmission system under grid-following control and grid-forming control.

[0125] In the above step 4.1, according to the simulated harmonic suppression results of the fan under the grid-following control and the grid-forming control, an oscilloscope can be introduced to collect the dynamic response curve data. The oscilloscope can be selected, for example, an oscilloscope with a sampling frequency set to 10kHz and recording 512 sampling points. Then, according to the amplitude and phase angle of each harmonic component in the dynamic response curve, the damping ratio calculation formula is used to calculate the damping ratio of the fan under the grid-following control and the grid-forming control. Then, according to the calculated damping ratio, the fan damping ratio and the ability to reduce the oscillation risk caused by the damping ratio are evaluated under the grid-forming and grid-following control modes; for example: at a frequency of 50Hz, the DC side impedance amplitude of the fan is 5 ohms and the phase angle is -75 degrees, and the AC side impedance amplitude is 2 ohms and the phase angle is -60 degrees. For the grid-following control mode, the damping ratio calculation formula ζ=R / 2(L / C) is adopted, where R is 2 ohms, L is 0.3 Henry, and C is 800 microfarads. The damping ratio under the grid-following control is calculated to be 12. For the grid-building control mode, the impedance parameters are the same, and the damping ratio under the grid-building control is calculated to be 15. Comparing the damping ratios under the two control modes, the damping ratio under the grid-building control mode is larger, and it is judged that the grid-building control mode can improve the system damping. By comparing the damping ratios, the damping ratio of the grid-building control mode is increased by 25%, which can effectively reduce the oscillation risk caused by the fan. According to the damping ratio comparison results of 30 groups under different working conditions, the support vector machine algorithm can be used to select the Gaussian kernel function. The penalty factor C of the Gaussian kernel function can be selected as 10, and the prediction model of the grid-building control mode to improve the system damping is obtained by training, and the cross-validation accuracy rate is more than 90%. By using the trained prediction model of grid-type control to improve system damping, it is determined that under the condition of transmission system impedance change of ±20%, the grid-type control method can still increase the system damping ratio by more than 20%, verifying its good effect and adaptability in reducing the risk of oscillation caused by wind turbines. It is then determined that the amplitude and phase angle of each harmonic component in the dynamic response curve are correlated with the impact of wind turbines on the stability of the transmission system under grid-type control and grid-type control.

[0126] In the above step 4.2: the total harmonic distortion value of the dynamic response curve can be obtained according to the amplitude and phase angle of each harmonic component. For example: calculate the total harmonic distortion THD = (I2 2 +I3 2 +........+I 50 2 ) / I1×100%, where I1 is the amplitude of the fundamental component, I2~I 50It is the amplitude of the 2nd to 50th harmonic component. If the total harmonic distortion THD exceeds 5%, it is judged that there is a large harmonic distortion. The analysis found that the amplitudes of the 3rd, 5th, and 7th harmonic components are large and are the main source of harmonic distortion, of which the 3rd harmonic accounts for 45%, the 5th harmonic accounts for 30%, and the 7th harmonic accounts for 20%. The relationship between the wind turbine impedance Z and the amplitude of each harmonic I is fitted by the least squares method, and the mathematical model I=kZα is obtained, where k and α are fitting coefficients. The dynamic response curves under the grid-forming control and the grid-following control are tested respectively, and the THD is calculated. It is 3% under the grid-forming control and 5% under the grid-following control, indicating that the harmonic distortion of the grid-forming control is smaller.

[0127] In the above step 4.3: the source of the harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component can be determined according to the total harmonic distortion value; the support vector machine algorithm can be used to classify the harmonic distortion data of the two control methods for the data in step 4.2 to determine the source of the harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component.

[0128] In the above step 4.4: based on the source of the harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component, the main source of the harmonic distortion can be determined, the frequency distribution characteristics of the harmonic components can be analyzed, and then the relationship between the harmonic amplitude and the wind turbine impedance, and the correlation between the harmonic distortion and the control method can be analyzed.

[0129] In the above step 4.5: based on the relationship between the harmonic amplitude and the impedance of the wind turbine, and the correlation between the harmonic distortion and the control method, the impact of the wind turbine on the stability of the transmission system under the grid-following control and grid-forming control can be quantitatively evaluated.

[0130] In the above steps 4.1-4.5, the dynamic response curve data of the wind turbine is obtained, and the fast Fourier transform is used for the data to obtain the amplitude and phase information of each harmonic component. According to the amplitude of each harmonic component, the total harmonic distortion rate is calculated. The harmonic distortion rate can also be used to determine the harmonic distortion. A threshold is preset for the total harmonic distortion rate. If the total harmonic distortion rate exceeds the preset threshold, it is judged that there is a large harmonic distortion. The amplitude of each harmonic component is analyzed to determine the main source of harmonic distortion, and the distribution characteristics of harmonic components of different frequencies are statistically analyzed. The relationship between the harmonic amplitude and the impedance of the wind turbine is quantitatively described by the curve fitting method. The dynamic response curves under different control modes are obtained, and the harmonic distortion of the grid-forming control and the grid-following control are compared and analyzed to obtain the difference in harmonic distortion between the two control modes. For the harmonic distortion data of the grid-forming control and the grid-following control, the support vector machine algorithm is used for classification, and the influence of the wind turbine on the stability of the transmission system under the grid-following control and the grid-forming control is quantitatively evaluated. In addition, based on the analysis results of harmonic distortion, the control circuit design and control parameters of the fan can be optimized to minimize harmonic distortion and improve power quality while ensuring dynamic response performance.

[0131] In step 4.1, after calculating the amplitude and phase angle of each harmonic component in the dynamic response curve based on the simulated harmonic suppression result, the following may also be included:

[0132] Based on the amplitude and phase angle of each harmonic component in the dynamic response curve, a damping ratio calculation method is used to calculate the damping ratio of the fan in two control modes: a grid-following type and a grid-forming type;

[0133] Based on the damping ratio of the wind turbine in the two control modes of following the grid and forming the grid, the ability of the wind turbine to reduce the oscillation risk in the two control modes of following the grid and forming the grid is determined.

[0134] The present invention application is aimed at the application scenario of power transmission system, and provides a stability analysis method for analyzing the grid-following type and grid-forming type wind turbines connected to the power transmission system on the grid-connected side of the wind turbine. It gives an impedance modeling method that takes into account both practical engineering application and modeling accuracy, and considers the harmonic domain modeling method to establish the impedance model of the wind turbine under grid-following type control and grid-forming type control, which is used to compare the influence of grid-following type and grid-forming type wind turbines on the stability of the DC and AC sides, so as to determine the effect of the internal parameters of the wind turbine on the AC and DC stability of the power transmission system.

[0135] Embodiment 2:

[0136] like Figure 2 As shown, the present invention provides a system for evaluating the stability of a power transmission system using a wind turbine control strategy, comprising:

[0137] A model building module, for establishing an impedance model of a wind turbine connected to a power transmission system using a harmonic domain modeling method under grid-following control and grid-forming control based on simulation data of the wind turbine connected to a power transmission system, wherein the simulation data includes topological structure parameters and controller parameters of the wind turbine;

[0138] A dynamic response curve acquisition module is used to simulate and analyze the impedance model of the wind turbine under the grid-following control and the grid-forming control, and to obtain a dynamic response curve of the fluctuation amplitude of the operation data of the wind turbine over time under the grid-following control and the grid-forming control;

[0139] A simulation harmonic suppression result acquisition module is used to perform spectrum analysis on the dynamic response curve to obtain simulation harmonic suppression results of the wind turbine under grid-following control and grid-forming control;

[0140] The stability impact assessment module is used to assess the stability impact of the wind turbine on the power transmission system under grid-following control and grid-forming control based on the simulation harmonic suppression results.

[0141] Furthermore, the dynamic response curve acquisition module includes:

[0142] A simulation circuit construction submodule is used to construct a simulation circuit of a flexible direct current transmission system for connecting a wind farm to the grid using simulation software based on an impedance model of the wind turbine under grid-following control and grid-forming control;

[0143] A simulation circuit setting submodule, used to set the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller in the simulation circuit of the flexible DC power transmission system;

[0144] The dynamic response curve acquisition submodule is used to perform small signal analysis on the flexible DC transmission system simulation circuit after setting, and obtain the dynamic response curve of the fluctuation amplitude of the wind turbine operation data changing with time under the grid-following control and the grid-forming control.

[0145] Furthermore, the simulation harmonic suppression result acquisition module includes:

[0146] An extraction submodule, used for extracting the magnitude, change trend and frequency distribution range of the fluctuation amplitude from the dynamic response curve;

[0147] A relationship analysis submodule, used for analyzing the relationship between the fluctuation amplitude and the frequency based on the size of the fluctuation amplitude, the change trend and the frequency distribution range;

[0148] A frequency domain characteristic determination submodule, used to determine the frequency domain characteristic of the fluctuation amplitude based on the relationship between the fluctuation amplitude and the frequency;

[0149] The simulation harmonic suppression result acquisition submodule is used to perform spectrum analysis on the dynamic response curve based on the frequency domain characteristics of the fluctuation amplitude, and obtain the simulation harmonic suppression results of the wind turbine under grid-following control and grid-forming control.

[0150] Furthermore, the stability impact assessment module includes:

[0151] An amplitude and phase angle calculation submodule, used to calculate the amplitude and phase angle of each harmonic component in the dynamic response curve based on the simulated harmonic suppression result;

[0152] A total harmonic distortion value acquisition submodule, used to acquire a total harmonic distortion value of the dynamic response curve based on the amplitude and phase angle of each harmonic component;

[0153] A harmonic determination submodule, used to determine the source of harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component based on the total harmonic distortion value;

[0154] A correlation determination submodule, for determining the relationship between the harmonic amplitude and the impedance of the wind turbine, and the correlation between the harmonic distortion and the control strategy based on the source of the harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component;

[0155] The stability impact assessment submodule is used to assess the impact of the wind turbine on the stability of the power transmission system under grid-following control and grid-forming control based on the relationship between the harmonic amplitude and the impedance of the wind turbine and the correlation between the harmonic distortion and the control strategy.

[0156] Furthermore, the system further comprises:

[0157] A damping ratio calculation module, for calculating the damping ratio of the fan in two control modes, a grid-following type and a grid-forming type, by using a damping ratio calculation method based on the amplitude and phase angle of each harmonic component in the dynamic response curve;

[0158] The oscillation risk reduction capability determination module is used to determine the oscillation risk reduction capability of the wind turbine under the two control modes of following the grid and building the grid based on the damping ratio of the wind turbine under the two control modes of following the grid and building the grid.

[0159] Furthermore, the system further comprises:

[0160] a relationship determination module, used to change the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller in the flexible DC power transmission system simulation circuit, and determine the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the power transmission system impedance;

[0161] The optimal combination determination module is used to determine the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller when suppressing harmonics based on the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the power transmission system.

[0162] Furthermore, the system further comprises:

[0163] A measured data acquisition module, used to apply the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller to an actual power transmission system, and to acquire the measured data of the wind turbine in the actual power transmission system;

[0164] A measured harmonic suppression result acquisition module is used to determine the measured harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control based on the measured data of the wind turbine;

[0165] An accuracy verification module is used to verify the accuracy of the impedance model of the wind turbine under grid-following control and grid-forming control based on the simulated harmonic suppression results of the wind turbine under grid-following control and grid-forming control and the measured harmonic suppression results.

[0166] Furthermore, the topological structure parameters of the wind turbine include: the number of submodules of the topological structure, the capacitance value of the topological structure, and the inductance value of the reactor of the topological structure;

[0167] The control system parameters of the fan include: a proportional coefficient and an integral coefficient of a controller in the control system.

[0168] Furthermore, the model building module is specifically used to establish the impedance model of the wind turbine under grid-following control and grid-forming control by using the harmonic domain modeling method for the AC current loop, DC voltage loop and circulating current suppression loop of the wind turbine in the topology structure based on the topology parameters and controller parameters of the wind turbine connected to the transmission system.

[0169] Embodiment 3:

[0170] In addition to the evaluation of the wind turbine control strategy on the stability of the power transmission system provided in the above embodiment, the present invention application also provides another method for evaluating the stability of the power transmission system by the wind turbine control strategy, comprising the following steps:

[0171] Step S1: constructing an impedance model of the wind turbine under grid-following control and grid-forming control according to the topological structure parameters and controller parameters of the wind turbine connected to the power transmission system;

[0172] Step S2: based on the impedance model of the wind turbine under the grid-following control and the grid-forming control, determining the dynamic response curve of the wind turbine under the grid-following control and the grid-forming control;

[0173] Step S3: Performing spectrum analysis on the dynamic response curve of the wind turbine to obtain simulation harmonic suppression results of the wind turbine under grid-following control and grid-forming control;

[0174] Step S4: According to the simulation harmonic suppression result, the effect of the internal parameters of the wind turbine on the stability of the AC and DC sides of the power grid is determined.

[0175] In step S1, constructing the impedance model of the wind turbine under the grid-following control and the grid-forming control may include:

[0176] According to the topological structure parameters and controller parameters of the wind turbine connected to the transmission system, the AC current loop, DC voltage loop and circulating current suppression loop of the wind turbine are obtained. Then, the harmonic domain modeling method is used to establish the impedance model of the wind turbine under grid-following control and grid-forming control.

[0177] In step S2, the impedance model of the wind turbine under the grid-following control and grid-forming control can be established as follows: Figure 3 The flexible direct current transmission system simulation circuit shown in the figure may include: a wind turbine, a controller, a plurality of upper bridge arms and a plurality of lower bridge arms; each upper bridge arm may include a plurality of first submodules (SM1, SM2, .... SM2) connected in series in sequence N ), the first resistor R arm , the first inductor L arm , a plurality of first submodules connected in series are connected in series with a first resistor as a whole, and the first resistor is connected in series with a first inductor; each lower bridge arm includes a plurality of second submodules (SM1, SM2, .... SM2) connected in series in sequence N ), the second resistor R arm , the second inductor L arm The plurality of second submodules connected in series are connected in series with a second resistor as a whole, and the second resistor is connected in series with a second inductor; the first inductor in each upper bridge arm is connected in series with the second inductor in the corresponding lower bridge arm. The connection point PCC between the upper bridge arm and the lower bridge arm is electrically connected to the wind turbine, and the wind turbine is electrically connected to the controller. Figure 3 in,u dc is the DC voltage of the simulation circuit of the flexible DC transmission system, i dc is the DC voltage of the simulation circuit of the flexible DC transmission system, C m The capacitance in the first submodule or the second submodule, Z dc Resistance in the simulation circuit of the flexible DC transmission system.

[0178] Then, the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller are set in the simulation circuit of the flexible DC transmission system. The simulation circuit of the flexible DC transmission system is processed by the small signal analysis method to determine the dynamic response curve of the fluctuation amplitude of the wind turbine's operating data changing with time under the grid-following control and grid-forming control.

[0179] Finally, for the simulation circuit of the set flexible DC transmission system, the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller can be changed according to the topological structure parameters and controller parameters of the wind turbine connected to the transmission system; the power level equation of the wind turbine, the admittance of the wind turbine, the small signal model of the AC side disturbance caused by power, and the impedance matrix of the wind turbine under grid-following control and grid-forming control are obtained; according to the power level equation of the wind turbine, the admittance of the wind turbine, the small signal model of the AC side disturbance of the transmission system caused by power, and the impedance matrix of the wind turbine under grid-following control and grid-forming control, the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller is determined; the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller can be used in the actual transmission system, and compared with the harmonic suppression results of the impedance model of the wind turbine under grid-following control and grid-forming control to verify the accuracy of the impedance model of the wind turbine under grid-following control and grid-forming control.

[0180] The process of constructing the power level equation is as follows: based on the matrix of currents of the upper bridge arm and the lower bridge arm, and the matrix of voltages of the upper bridge arm and the lower bridge arm in the simulation circuit of the flexible direct current transmission system, the power level equation is determined.

[0181] Among them, the process of determining the small signal model of the AC side disturbance of the transmission system caused by power includes: inputting AC and DC into the simulation circuit of the flexible DC transmission system respectively; analyzing the influence of active power and DC voltage control, the influence of AC voltage control on the wind turbine, the influence of reactive power control on the wind turbine, the influence of virtual impedance control and circulating current suppression of the wind turbine on the simulation circuit of the flexible DC transmission system in turn; and then analyzing the disturbance caused by the control mode of the wind turbine to the simulation circuit of the flexible DC transmission system under the grid-following control and grid-forming control of the wind turbine; determining the disturbance caused by the control mode of the wind turbine to the simulation circuit of the flexible DC transmission system as the small signal model under the AC side disturbance caused by power;

[0182] Among them, the disturbances caused by the control method of the wind turbine on the simulation circuit of the flexible DC transmission system include: the disturbances caused by the active power and DC voltage control of the wind turbine on the simulation circuit of the flexible DC transmission system, the influence of AC voltage control on the simulation circuit of the flexible DC transmission system, the influence of reactive power control on the simulation circuit of the flexible DC transmission system, and the influence of virtual impedance control and circulating current suppression on the simulation circuit of the flexible DC transmission system.

[0183] The above-mentioned step S3 may include: extracting the size, change trend and frequency distribution range of the fluctuation amplitude in the dynamic response curve, then analyzing the relationship between the fluctuation amplitude and the frequency, then determining the frequency domain characteristics of the fluctuation amplitude, and finally performing spectrum analysis on the dynamic response curve to obtain the simulated harmonic suppression results of the fan under grid-following control and grid-forming control.

[0184] In step S4, based on the simulation harmonic suppression results, the Nyquist criterion can be used to analyze the stability impact of the wind turbine in the grid-following control and grid-configuration type on the interaction of the transmission system; the impact of the number of wind turbines connected on the stability of the transmission system under different grid access intensities can be compared.

[0185] Mainly based on the simulation harmonic suppression results, the amplitude and phase angle of each harmonic component in the dynamic response curve are calculated, and then the total harmonic distortion rate value of the dynamic response curve is obtained, and then the source of the harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component are determined. Finally, the relationship between the harmonic amplitude and the impedance of the wind turbine, the correlation between the harmonic distortion and the control strategy are determined, so as to evaluate the impact of the wind turbine on the stability of the transmission system under grid-following control and grid-forming control.

[0186] Among them, the impact on stability can include: analyzing the damping effect of the impedance of the DC side of the wind turbines controlled by the grid and the wind turbines controlled by the grid; analyzing the impact of the wind turbine impedance and feeder impedance on the DC impedance of the renewable energy side of the transmission system under the grid-following control and the grid-forming control; analyzing the impact of the number of wind turbines and the proportional coefficient of the controller on the DC impedance of the renewable energy side of the transmission system; when analyzing the impact on stability, the impact of transformers and DC cables can be ignored.

[0187] Considering that the traditional impedance modeling method is difficult to take into account both the actual application of engineering and the accuracy of modeling, the stability analysis results deviate from the actual situation. In addition, when considering the harmonic transfer function within the third harmonic, how to establish the impedance model of grid-type control is also a thorny problem. The existing wind turbine grid-type and grid-type control impedance models are not perfect, and it is impossible to accurately compare the impact of the two control methods on the stability of the DC side and the AC side. At the same time, the mechanism of action of the internal parameters of the fan on the stability of the AC and DC sides is still unclear, and there is a lack of quantitative analysis and theoretical basis for guiding parameter optimization. In the embodiment of the present invention, a new impedance modeling method is proposed, which can ensure the practicality of the project while improving the accuracy of modeling, and establish a complete wind turbine grid-type and grid-type control impedance model, revealing the intrinsic connection between the internal parameters of the fan and the stability of the AC and DC sides, and providing a reliable theoretical basis and technical support for the stability analysis of the new energy grid-connected grid-type flexible direct current application.

[0188] Embodiment 4:

[0189] like Figure 4As shown, the present invention also provides an electronic device, which may be a computer device, a single-chip device, an intelligent mobile device, etc. The electronic device in this embodiment may include a processor, a memory, a transceiver component, etc. The memory, the processor, and the transceiver component are connected via a bus; the memory may be used to store an execution program, and an exemplary execution program may include instructions; the processor is used to execute the instructions stored in the memory. The memory may also be used to store data, which may be called and / or modified when the instructions are executed.

[0190] The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in a storage medium to implement corresponding method flows or corresponding functions, so as to implement the steps of a method for evaluating the stability of a power transmission system by a wind turbine control strategy in the above-mentioned embodiment.

[0191] Embodiment 5:

[0192] Based on the same inventive concept, the present invention also provides a readable storage medium, specifically an electronic device readable storage medium (Memory), which is a memory device in the electronic device for storing programs and data. It can be understood that the storage medium here can include both the built-in storage medium in the electronic device and the extended storage medium supported by the electronic device. The storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by the processor are also stored in the storage space, and these instructions can be one or more execution programs (including program codes). It should be noted that the storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor loads and executes one or more instructions stored in the storage medium, which can implement the steps of a method for evaluating the stability of a power transmission system by a wind turbine control strategy in the above embodiment.

[0193] Those skilled in the art will appreciate that the embodiments of the present invention application can be provided as methods, systems, or computer program products. Therefore, the present invention application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present invention application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0194] The present invention application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present invention application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0195] These computer program instructions may also be stored in a computer readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0196] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0197] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention application rather than to limit its protection scope. Although the present invention application is described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that after reading the present invention application, those skilled in the art can still make various changes, modifications or equivalent substitutions to the specific implementation methods of the application, but these changes, modifications or equivalent substitutions are all within the protection scope of the claims to be approved.

Claims

1. A method for evaluating the stability of a power transmission system using a wind turbine control strategy, characterized in that: include: Based on the simulation data of the wind turbine connected to the power transmission system, the impedance model of the wind turbine under the grid-following control and the grid-forming control is established by using the harmonic domain modeling method, wherein the simulation data includes the topological structure parameters and the controller parameters of the wind turbine; Simulating and analyzing the impedance model of the wind turbine under the grid-following control and the grid-forming control, and obtaining a dynamic response curve of the fluctuation amplitude of the operation data of the wind turbine over time under the grid-following control and the grid-forming control; Performing spectrum analysis on the dynamic response curve to obtain simulated harmonic suppression results of the wind turbine under grid-following control and grid-forming control; Based on the simulation harmonic suppression results, the impact of the wind turbine on the stability of the power transmission system under grid-following control and grid-forming control is evaluated.

2. The method according to claim 1, characterized in that: The impedance model of the wind turbine under the grid-following control and the grid-forming control is simulated and analyzed to obtain the dynamic response curve of the fluctuation amplitude of the operation data of the wind turbine under the grid-following control and the grid-forming control over time, including: Based on the impedance model of the wind turbine under the grid-following control and the grid-building control, a simulation circuit of the flexible direct current transmission system for the wind farm grid connection is constructed by using simulation software; Setting the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller in the flexible DC power transmission system simulation circuit; The set flexible direct current transmission system simulation circuit is processed by a small signal analysis method to obtain a dynamic response curve of the fluctuation amplitude of the wind turbine operation data changing with time under the grid-following control and the grid-forming control.

3. The method according to claim 1, characterized in that The spectrum analysis of the dynamic response curve is performed to obtain the simulated harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control, including: Extracting the magnitude, variation trend and frequency distribution range of the fluctuation amplitude from the dynamic response curve; Based on the magnitude of the fluctuation amplitude, the variation trend and the frequency distribution range, analyzing the relationship between the fluctuation amplitude and the frequency; Based on the relationship between the fluctuation amplitude and the frequency, determining the frequency domain characteristics of the fluctuation amplitude; Based on the frequency domain characteristics of the fluctuation amplitude, the dynamic response curve is subjected to spectrum analysis to obtain the simulated harmonic suppression results of the wind turbine under grid-following control and grid-forming control.

4. The method according to claim 1, characterized in that: The evaluating the influence of the wind turbine on the stability of the power transmission system under the grid-following control and the grid-forming control based on the simulation harmonic suppression result includes: Based on the simulated harmonic suppression result, calculating the amplitude and phase angle of each harmonic component in the dynamic response curve; Based on the amplitude and phase angle of each harmonic component, obtaining a total harmonic distortion value of the dynamic response curve; Based on the total harmonic distortion value, determining the source of harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component; Based on the sources of harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component, determining the relationship between the harmonic amplitude and the impedance of the wind turbine, and the correlation between the harmonic distortion and the control strategy; Based on the relationship between the harmonic amplitude and the impedance of the wind turbine, and the correlation between the harmonic distortion and the control strategy, the impact of the wind turbine on the stability of the power transmission system under grid-following control and grid-forming control is evaluated.

5. The method according to claim 4, characterized in that After calculating the amplitude and phase angle of each harmonic component in the dynamic response curve based on the simulated harmonic suppression result, the method further includes: Based on the amplitude and phase angle of each harmonic component in the dynamic response curve, a damping ratio calculation method is used to calculate the damping ratio of the fan in two control modes: a grid-following type and a grid-forming type; Based on the damping ratio of the wind turbine in the two control modes of following the grid and forming the grid, the ability of the wind turbine to reduce the oscillation risk in the two control modes of following the grid and forming the grid is determined.

6. The method according to claim 2, characterized in that After the flexible DC power transmission system simulation circuit is processed by a small signal analysis method to obtain a dynamic response curve of the fluctuation amplitude of the wind turbine operation data changing with time under the grid-following control and the grid-forming control, the method further includes: In the flexible direct current transmission system simulation circuit, the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller are changed to determine the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the transmission system; Based on the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the power transmission system, the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller and the integral coefficient of the controller when suppressing harmonics is determined.

7. The method according to any one of claims 1 to 6, characterized in that: After determining the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller when suppressing harmonics based on the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the power transmission system, the method further includes: Applying the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller to an actual power transmission system, and obtaining actual measured data of the wind turbine in the actual power transmission system; Based on the measured data of the wind turbine, determining the measured harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control; Based on the simulated harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control and the measured harmonic suppression results, the accuracy of the impedance model of the wind turbine under the grid-following control and the grid-forming control is verified.

8. The method according to claim 1, characterized in that: The topological structure parameters of the wind turbine include: the number of submodules of the topological structure, the capacitance value of the topological structure, and the inductance value of the reactor of the topological structure; The control system parameters of the fan include: a proportional coefficient and an integral coefficient of a controller in the control system.

9. The method according to claim 1, characterized in that: The impedance model of the wind turbine under grid-following control and grid-forming control is established by using the harmonic domain modeling method based on the simulation data of the wind turbine connected to the power transmission system, including: Based on the topological structure parameters and controller parameters of the wind turbine connected to the transmission system, the harmonic domain modeling method is used to establish the impedance model of the wind turbine under grid-following control and grid-forming control for the AC current loop, DC voltage loop and circulating current suppression loop of the wind turbine in the topological structure.

10. A system for evaluating the stability of a power transmission system using a wind turbine control strategy, characterized in that: include: A model building module, for establishing an impedance model of a wind turbine connected to a power transmission system using a harmonic domain modeling method under grid-following control and grid-forming control based on simulation data of the wind turbine connected to a power transmission system, wherein the simulation data includes topological structure parameters and controller parameters of the wind turbine; A dynamic response curve acquisition module is used to simulate and analyze the impedance model of the wind turbine under the grid-following control and the grid-forming control, and to obtain a dynamic response curve of the fluctuation amplitude of the operation data of the wind turbine over time under the grid-following control and the grid-forming control; A simulation harmonic suppression result acquisition module is used to perform spectrum analysis on the dynamic response curve to obtain simulation harmonic suppression results of the wind turbine under grid-following control and grid-forming control; The stability impact assessment module is used to assess the stability impact of the wind turbine on the power transmission system under grid-following control and grid-forming control based on the simulation harmonic suppression results.

11. The system according to claim 10, characterized in that The dynamic response curve acquisition module includes: A simulation circuit construction submodule is used to construct a simulation circuit of a flexible direct current transmission system for connecting a wind farm to the grid using simulation software based on an impedance model of the wind turbine under grid-following control and grid-forming control; A simulation circuit setting submodule, used to set the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller in the simulation circuit of the flexible DC power transmission system; The dynamic response curve acquisition submodule is used to perform small signal analysis on the flexible DC transmission system simulation circuit after setting, and obtain the dynamic response curve of the fluctuation amplitude of the wind turbine operation data changing with time under the grid-following control and the grid-forming control.

12. The system according to claim 10, characterized in that The simulation harmonic suppression result acquisition module includes: An extraction submodule, used for extracting the magnitude, change trend and frequency distribution range of the fluctuation amplitude from the dynamic response curve; A relationship analysis submodule, used for analyzing the relationship between the fluctuation amplitude and the frequency based on the size of the fluctuation amplitude, the change trend and the frequency distribution range; A frequency domain characteristic determination submodule, used to determine the frequency domain characteristic of the fluctuation amplitude based on the relationship between the fluctuation amplitude and the frequency; The simulation harmonic suppression result acquisition submodule is used to perform spectrum analysis on the dynamic response curve based on the frequency domain characteristics of the fluctuation amplitude, and obtain the simulation harmonic suppression results of the wind turbine under grid-following control and grid-forming control.

13. The system according to claim 10, characterized in that The stability impact assessment module comprises: An amplitude and phase angle calculation submodule, used to calculate the amplitude and phase angle of each harmonic component in the dynamic response curve based on the simulated harmonic suppression result; A total harmonic distortion value acquisition submodule, used to acquire a total harmonic distortion value of the dynamic response curve based on the amplitude and phase angle of each harmonic component; A harmonic determination submodule, used to determine the source of harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component based on the total harmonic distortion value; A correlation determination submodule, for determining the relationship between the harmonic amplitude and the impedance of the wind turbine, and the correlation between the harmonic distortion and the control strategy based on the source of the harmonic distortion of each harmonic component and the frequency distribution characteristics of each harmonic component; The stability impact assessment submodule is used to assess the impact of the wind turbine on the stability of the power transmission system under grid-following control and grid-forming control based on the relationship between the harmonic amplitude and the impedance of the wind turbine and the correlation between the harmonic distortion and the control strategy.

14. The system according to claim 13, characterized in that The system further comprises: A damping ratio calculation module, for calculating the damping ratio of the fan in two control modes, a grid-following type and a grid-forming type, by using a damping ratio calculation method based on the amplitude and phase angle of each harmonic component in the dynamic response curve; The oscillation risk reduction capability determination module is used to determine the oscillation risk reduction capability of the wind turbine under the two control modes of following the grid and building the grid based on the damping ratio of the wind turbine under the two control modes of following the grid and building the grid.

15. The system according to claim 11, characterized in that The system further comprises: a relationship determination module, used to change the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller in the flexible DC power transmission system simulation circuit, and determine the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the power transmission system impedance; The optimal combination determination module is used to determine the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller when suppressing harmonics based on the relationship between the rotor inertia of the wind turbine, the proportional coefficient of the controller, the integral coefficient of the controller and the impedance of the power transmission system.

16. The system according to any one of claims 10 to 15, characterized in that: The system further comprises: A measured data acquisition module, used to apply the optimal combination of the rotor inertia of the wind turbine, the proportional coefficient of the controller, and the integral coefficient of the controller to an actual power transmission system, and to acquire the measured data of the wind turbine in the actual power transmission system; A measured harmonic suppression result acquisition module is used to determine the measured harmonic suppression results of the wind turbine under the grid-following control and the grid-forming control based on the measured data of the wind turbine; An accuracy verification module is used to verify the accuracy of the impedance model of the wind turbine under grid-following control and grid-forming control based on the simulated harmonic suppression results of the wind turbine under grid-following control and grid-forming control and the measured harmonic suppression results.

17. The system according to claim 10, characterized in that The topological structure parameters of the wind turbine include: the number of submodules of the topological structure, the capacitance value of the topological structure, and the inductance value of the reactor of the topological structure; The control system parameters of the fan include: a proportional coefficient and an integral coefficient of a controller in the control system.

18. The system according to claim 10, characterized in that The model building module is specifically used to establish the impedance model of the wind turbine under grid-following control and grid-forming control by using the harmonic domain modeling method based on the topological structure parameters and controller parameters of the wind turbine connected to the power transmission system, for the AC current loop, DC voltage loop and circulating current suppression loop of the wind turbine in the topological structure.

19. An electronic device, characterized in that: include: at least one processor and memory; The memory and the processor are connected via a bus; The memory is used to store one or more programs; When the one or more programs are executed by the at least one processor, the method for evaluating the stability of a power transmission system using a wind turbine control strategy as described in any one of claims 1 to 9 is implemented.

20. A readable storage medium, characterized in that: An execution program is stored thereon, and when the execution program is executed, the method for evaluating the stability of the power transmission system by the wind turbine control strategy according to any one of claims 1 to 9 is implemented.

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