Method and system for rapidly evaluating grid-connected stability of wind power plant based on impedance model

Abstract

The invention discloses a wind power plant grid-connected stability rapid evaluation method and system based on an impedance model, and relates to the technical field of power grid systems, and the method comprises the steps: S1, building a physical model of a wind power plant grid-connected system; s2, establishing an impedance model of a wind power plant and a power grid; s3, selecting a proper evaluation index; s4, performing impedance matching analysis; s5, evaluating dynamic response characteristics; s6, performing steady-state analysis; s7, evaluating the influence of grid connection on the power grid; and S8, designing a control strategy, and building the system based on the method. According to the wind power plant grid-connected stability rapid evaluation method and system based on the impedance model, comprehensive and rapid evaluation of the wind power plant grid-connected stability is realized by constructing the accurate wind power plant and power grid impedance model and combining various evaluation indexes and control strategies, and potential stability problems can be effectively identified and solved; and powerful support is provided for safe and efficient grid connection of the wind power plant.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid systems, and in particular to a method and system for quickly evaluating the grid-connected stability of a wind farm based on an impedance model. Background Art

[0002] In the development of wind farm grid-connected technology, how to accurately and quickly evaluate the stability between wind farms and power grids has always been the focus and difficulty of research. Traditional wind farm grid-connected stability assessment methods often rely on complex simulation models and long-term experimental data accumulation. These methods are not only time-consuming, but also difficult to reflect the dynamic interaction characteristics of wind farms and power grids in real time. In addition, the existing technology lacks in-depth analysis of wind farm and power grid impedance characteristics, which makes it difficult to accurately capture potential stability problems during the assessment process. Especially in the context of high penetration of wind power access to the grid, the randomness and volatility of wind farms have an increasingly significant impact on the stability of the power grid, and traditional assessment methods can no longer meet the needs of the current power system. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides a method and system for quickly evaluating the grid-connected stability of a wind farm based on an impedance model to solve the problems raised in the above-mentioned background technology.

[0004] To achieve the above object, the present invention provides the following technical solution: a method for rapid assessment of wind farm grid connection stability based on impedance model, comprising the following steps:

[0005] S1. Establish the physical model of the wind farm grid-connected system

[0006] Collect data on the wind farm grid-connected system, analyze the overall structure and parameters of the wind farm grid-connected system, and build a physical model of the wind farm grid-connected system. The physical model shows the interaction between the various components in the system and provides a framework for subsequent impedance modeling;

[0007] S2. Establish impedance model of wind farm and power grid

[0008] The impedance model of the wind farm includes the impedance of the wind turbine system, the impedance of the converter and the total impedance of the wind farm; the impedance model of the power grid includes the impedance of the transmission line, the impedance of the transformer and the load impedance of the power grid. By calculating the impedance of the wind farm and the power grid, the complex impedance matrix of the wind farm grid-connected system is obtained.

[0009] S3. Choose appropriate evaluation metrics

[0010] Determine the evaluation indicators to measure the stability of the wind farm grid-connected system, including voltage stability, frequency stability, and power factor; when selecting the evaluation indicators, consider the characteristics of the wind farm and the requirements of the power grid, such as selecting indicators of voltage transient response, frequency response, and power fluctuation for analysis;

[0011] S4. Perform impedance matching analysis

[0012] By comparing the impedance of the wind farm and the grid, the stability of the system is judged. Impedance matching analysis is used to identify potential stability issues and ensure that the system remains stable in all operating frequency ranges.

[0013] S5. Evaluate dynamic response characteristics

[0014] Evaluate the wind farm's ability to respond to disturbances during the grid connection process, and observe the system's response behavior under disturbances by simulating the actual operation of the wind farm and the grid;

[0015] S6. Perform steady-state analysis

[0016] Evaluate the power balance, power factor, and voltage and frequency stability of the wind farm grid-connected system by calculating the system's power flow, load distribution, and the system's voltage and frequency stability to determine the system's stability under steady-state conditions;

[0017] S7. Evaluate the impact of grid connection on the power grid

[0018] Evaluate the impact of wind farm connection on the grid, determine whether it will have a negative impact on the stability of the grid, analyze grid voltage fluctuations, frequency changes and system harmonics, and use power system simulation tools to simulate and analyze the grid after connection;

[0019] S8. Design control strategy

[0020] The control strategy includes wind turbine power control, converter current control, and system voltage and frequency regulation. By designing control algorithms such as PID control and fuzzy control, the stability and performance of the system are improved, and multiple simulation tests are performed to determine the optimal control parameters and strategies.

[0021] To further optimize the technical solution, in step S1, the data of the wind farm grid-connected system includes wind speed and direction data, power generation data, wind turbine operation data, grid data, converter and electrical equipment data,

[0022] Environmental factor data as well as fault and anomaly data.

[0023] To further optimize the technical solution, in step S2, when establishing the impedance model of the wind farm:

[0024] Impedance Z of the fan system wind It is expressed as:

[0025] Z wind =R wind +jX wind

[0026] Among them, R wind is the resistance of the fan, X wind is the reactance of the fan;

[0027] The impedance Z of the converter converter It is expressed as:

[0028] Z converter =R converter +jX converter

[0029] Among them, R converter is the resistance of the converter, X converter is the reactance of the converter;

[0030] The total impedance of the wind farm is Z total The parallel impedance of the fan and converter is calculated as follows:

[0031]

[0032] When establishing the impedance model of the power grid:

[0033] The impedance of the transmission line Z line It is expressed as:

[0034] Z line =R line +jX line

[0035] Among them, R line is the resistance of the transmission line, X line is the reactance of the transmission line;

[0036] The impedance of the transformer is Z transformer It is expressed as:

[0037] Z transformer =R transformer +jX transformer

[0038] Among them, R transformer is the resistance of the transformer, X transformer is the reactance of the transformer;

[0039] The load impedance of the power grid is Z load It is expressed as:

[0040] Z load =R load+jX load

[0041] The total impedance of the power grid is Z grid It is expressed as:

[0042] Z grid =Z line +Z transformer +Z load

[0043] When calculating the complex impedance matrix of the wind farm grid-connected system:

[0044] Z system is the complex impedance matrix of the wind farm and the power grid, then the matrix is ​​expressed as:

[0045]

[0046] Among them, Z interface is the impedance of the interface between the wind farm and the grid.

[0047] To further optimize the technical solution, in step S4, a wind farm impedance analysis model and a power grid impedance analysis model are constructed, and frequency domain analysis is performed to check the impedance characteristics of the system at different frequencies;

[0048] The wind farm impedance analysis model is as follows:

[0049]

[0050] Among them, (Z wind (s)) is the impedance of the wind farm, where (s) is the complex frequency variable in Laplace transform, (R wind ) is the DC resistance of the wind farm, (L wind ) is the inductance of the wind farm, (τ wind ) is the time constant of the wind farm;

[0051] The grid impedance analysis model is as follows:

[0052]

[0053] Among them, (Z grid (s)) is the impedance of the grid, (R grid ) is the DC resistance of the grid, (L grid ) is the inductance of the grid, (τ grid ) is the time constant of the power grid, (C grid ) is the capacitance of the grid;

[0054] In the frequency domain analysis, different frequencies are selected, and the wind farm impedance analysis model and the power grid impedance analysis model are used to calculate the impedance of the wind farm and the power grid, and a frequency response diagram is drawn to compare the matching degree between the wind farm impedance and the power grid impedance.

[0055] To further optimize the technical solution, in step S5, when evaluating the response capability of the wind farm to disturbances during the grid connection process, the wind farm dynamic response model and the frequency domain response model are used for evaluation;

[0056] The wind farm dynamic response model is as follows:

[0057]

[0058] Where, (ΔV(t)) is the change in system voltage at time (t), (Pwind(t)) is the power generated by the wind farm at time (t), (Pload(t)) is the load power, (Vbase) is the reference voltage, and (Zwind) is the equivalent impedance of the wind farm;

[0059] The frequency domain response model is as follows:

[0060]

[0061] Where, (H(ω)) is the frequency domain response function, (ω) is the angular frequency, (T wind ) is the time constant of the wind farm system;

[0062] Through frequency domain analysis, we can understand the stability of the system at different frequencies.

[0063] To further optimize the technical solution, in step S6, the system has a built-in power balance model and a voltage stability model to evaluate the stability of the wind farm and the power grid in long-term operation;

[0064] The power balance model is as follows:

[0065] [P wind +P gen =P load +P loss ]

[0066] Among them, (P wind ) is the output power of the wind farm, (P gen ) is the output power of other power generation equipment, (P load ) is the load power demand of the power grid, (P loss ) is the power loss in the system;

[0067] The voltage stability model is as follows:

[0068]

[0069] Among them, (V bus ) is the grid bus voltage, (P load ) and (Q load ) are the active and reactive power of the load, respectively, (Z bus ) is the impedance of the grid bus.

[0070] To further optimize the technical solution, in step S7, when performing simulation analysis, the following process is specifically included:

[0071] Build simulation models, and build wind farm models and power grid models in power system simulation tools DIgSILENT PowerFactory, PSS / E, and MATLAB / Simulink;

[0072] Set up simulation scenarios to simulate the grid-connected operation of wind farms under normal wind speed and load conditions, and set up different fault and disturbance scenarios, such as sudden changes in wind speed, sudden increases and decreases in load, and grid faults, to observe the response of wind farms after grid connection;

[0073] Perform simulation analysis to conduct voltage fluctuation analysis, frequency variation analysis, and harmonic analysis.

[0074] To further optimize the technical solution, in step S8, in the control strategy:

[0075] Wind turbine power control, power regulation algorithms based on wind speed prediction and grid demand, such as maximum power point tracking (MPPT) combined with power limiting strategies, ensure that wind turbine output matches grid demand;

[0076] Current control of the converter, design the current control loop of the converter, including dq axis current control, using PI controller to quickly respond to grid current demand;

[0077] Voltage and frequency regulation, designing active regulation strategies for voltage and frequency, such as using droop control or virtual synchronous generator (VSG) technology, simulating the characteristics of conventional generators.

[0078] A wind farm grid-connected stability rapid assessment system based on an impedance model is constructed based on the above-mentioned wind farm grid-connected stability rapid assessment method based on an impedance model, and includes a data collection module, a model building module, an assessment index selection module, an impedance matching analysis module, a dynamic response assessment module, a steady-state analysis module, a power grid impact assessment module, and a control strategy design module;

[0079] A data collection module receives data from wind farms and power grids;

[0080] Model building module, which builds the physical model of the wind farm grid-connected system and the impedance model of the wind farm and the power grid;

[0081] Evaluation index selection module, which selects evaluation indexes based on user needs and wind farm characteristics;

[0082] Impedance matching analysis module, based on the impedance model of wind farm and power grid, outputs impedance matching analysis results;

[0083] Dynamic response assessment module, which evaluates the wind farm’s ability to respond to disturbances during the grid connection process;

[0084] Steady-state analysis module, to perform steady-state analysis of the system;

[0085] The grid impact assessment module evaluates the impact of wind farm grid connection on the grid, including grid voltage fluctuations, frequency changes and harmonics;

[0086] The control strategy design module designs the control strategy of the wind farm, including the power control of the wind turbine, the current control of the converter, and the voltage and frequency regulation of the system.

[0087] To further optimize the technical solution, the system also includes a data management module for recording all evaluation data, simulation results and test results and performing data backup, and generating reports based on the evaluation data, simulation results and test results.

[0088] Compared with the prior art, the present invention provides a method and system for rapid assessment of wind farm grid-connected stability based on an impedance model, which has the following beneficial effects:

[0089] This impedance model-based wind farm grid-connected stability rapid assessment method and system achieves a comprehensive and rapid assessment of wind farm grid-connected stability by constructing an accurate wind farm and grid impedance model and combining multiple assessment indicators and control strategies. This method not only improves the accuracy and real-time performance of the assessment, but also effectively identifies and solves potential stability problems, providing strong support for the safe and efficient grid connection of wind farms. At the same time, by designing a reasonable control strategy, the stability and performance of the wind farm grid-connected system are further improved, promoting the large-scale development and utilization of wind power resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Figure 1 A schematic diagram of a flow chart of a method for rapid assessment of wind farm grid-connected stability based on an impedance model proposed by the present invention;

[0091] Figure 2 A classification diagram of control strategies in a rapid assessment method for wind farm grid-connected stability based on an impedance model proposed by the present invention;

[0092] Figure 3A schematic diagram of the flow of simulation analysis in a method for rapid assessment of wind farm grid-connected stability based on an impedance model proposed by the present invention;

[0093] Figure 4 This is a structural flow chart of a wind farm grid-connected stability rapid assessment system based on an impedance model proposed by the present invention. DETAILED DESCRIPTION

[0094] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0095] Embodiment 1:

[0096] See also Figure 1 , a rapid assessment method for wind farm grid-connected stability based on impedance model, comprising the following steps:

[0097] S1. Establish the physical model of the wind farm grid-connected system

[0098] Collect data on the wind farm grid-connected system, analyze the overall structure and parameters of the wind farm grid-connected system, and build a physical model of the wind farm grid-connected system. The physical model shows the interaction between the components in the system and provides a framework for subsequent impedance modeling. All models require accurate parameter settings, such as wind speed, generator rated power, converter control parameters, grid impedance value, etc. These parameters will affect the stability analysis results of the system.

[0099] In this embodiment, the data of the wind farm grid-connected system includes wind speed and direction data, power generation data, wind turbine operation data, power grid data, converter and electrical equipment data, environmental factor data, and fault and abnormality data. The above data specifically includes:

[0100] Wind speed and direction data: Wind speed data reflects the wind energy resources in the area where the wind farm is located and is a key factor in evaluating the power generation potential and efficiency of the wind farm. Wind direction data has an important impact on the layout optimization of the wind farm and the wind turbine control strategy because it determines the main source direction of wind energy.

[0101] Power generation data: Power generation data records the actual power generation of a wind farm under different wind speed and wind direction conditions, and is an important indicator for evaluating the operating performance of a wind farm.

[0102] Wind turbine operating data: including wind turbine speed, blade angle, mechanical stress, etc. These data are essential for monitoring wind turbine operating status, predicting maintenance needs, and optimizing wind turbine performance.

[0103] Grid data: Grid data includes the voltage, frequency, power factor, etc. of the grid. These data reflect the stability and operating status of the grid and have an important impact on the stable operation of the wind farm after it is connected to the grid.

[0104] Converter and electrical equipment data: Converter is a key interface device between wind farms and power grids. Its operating data (such as current, voltage, power factor, etc.) is of great significance for evaluating the grid-connected performance and power quality of wind farms.

[0105] At the same time, the operating data of other electrical equipment in the wind farm (such as transformers, circuit breakers, cables, etc.) is also an important basis for evaluating the stability and safety of the system.

[0106] Environmental factor data: In addition to wind speed and direction, environmental factors such as temperature, humidity, air pressure, etc. may also have an impact on the operation of the wind farm. These data help to more comprehensively evaluate the operating environment and performance of the wind farm.

[0107] Fault and abnormal data: Records faults and abnormal conditions that occur during the grid connection process of wind farms, such as equipment failures and grid fluctuations. These data are of great significance for analyzing the causes of faults, formulating countermeasures, and optimizing system performance.

[0108] In the scenario application, the collected data types are presented in Table 1.

[0109]

[0110]

[0111] Table 1

[0112] S2. Establish impedance model of wind farm and power grid

[0113] The impedance model of the wind farm includes the impedance of the wind turbine system, the impedance of the converter and the total impedance of the wind farm. The impedance model of the power grid includes the impedance of the transmission line, the impedance of the transformer and the load impedance of the power grid. By calculating the impedance of the wind farm and the power grid, the complex impedance matrix of the wind farm grid-connected system is obtained. In this embodiment, when establishing the impedance model of the wind farm:

[0114] Impedance Z of the fan system wind It is expressed as:

[0115] Z wind =R wind +jX wind

[0116] Among them, R wind is the resistance of the fan, X wind is the reactance of the fan;

[0117] The impedance Z of the converter converter It is expressed as:

[0118] Z converter =R converter +jX converter

[0119] Among them, R converter is the resistance of the converter, X converter is the reactance of the converter;

[0120] The total impedance of the wind farm is Z total The parallel impedance of the fan and converter is calculated as follows:

[0121]

[0122] When establishing the impedance model of the power grid:

[0123] The impedance of the transmission line Z line It is expressed as:

[0124] Z line =R line +jX line

[0125] Among them, R line is the resistance of the transmission line, X line is the reactance of the transmission line;

[0126] The impedance of the transformer is Z transformer It is expressed as:

[0127] Z transformer =R transformer +jX transformer

[0128] Among them, R transformer is the resistance of the transformer, X transformer is the reactance of the transformer; the load impedance of the power grid is Z load It is expressed as:

[0129] Z load =R load +jX load

[0130] The total impedance of the power grid is Z grid It is expressed as:

[0131] Z grid =Z line +Ztransformer +Z load

[0132] When calculating the complex impedance matrix of the wind farm grid-connected system:

[0133] Z system is the complex impedance matrix of the wind farm and the power grid, then the matrix is ​​expressed as:

[0134]

[0135] Among them, Z interface is the impedance of the interface between the wind farm and the grid.

[0136] Based on the above model, the following steps are used to calculate the complex impedance matrix of the system:

[0137] Calculate the respective impedance models of the wind farm and the grid;

[0138] These impedance models are combined into a matrix that considers the interface impedance between the wind farm and the grid;

[0139] Through matrix operations (such as inversion or eigenvalue analysis), the complex impedance characteristics of the system can be obtained for subsequent stability analysis.

[0140] S3. Choose appropriate evaluation metrics

[0141] Stability assessment relies on a series of indicators to measure the stability of the system. These indicators include voltage stability, frequency stability, power factor, etc. When selecting evaluation indicators, the characteristics of the wind farm and the requirements of the power grid should be considered. For example, indicators such as voltage transient response, frequency response, and power fluctuation can be selected for analysis. The selection of each indicator should be based on the actual application scenario and system requirements to ensure that the evaluation results can truly reflect the stability of the system.

[0142] S4. Perform impedance matching analysis

[0143] By comparing the impedance of the wind farm and the grid, the stability of the system is judged. Impedance matching analysis is used to identify potential stability issues and ensure that the system remains stable in all operating frequency ranges.

[0144] In this embodiment, a wind farm impedance analysis model and a power grid impedance analysis model are constructed, and frequency domain analysis is performed to check the impedance characteristics of the system at different frequencies;

[0145] The wind farm impedance analysis model is as follows:

[0146]

[0147] Among them, (Z wind(s)) is the impedance of the wind farm, where (s) is the complex frequency variable in Laplace transform, (R wind ) is the DC resistance of the wind farm (such as the internal resistance of the wind turbine), (L wind ) is the inductance of the wind farm (such as the inductance of the wind turbine motor), (τ wind ) is the time constant of the wind farm (representing the dynamic response characteristics of the system).

[0148] When the model is used:

[0149] Impedance calculation: Substitute the actual wind farm parameters into the model to calculate the wind farm impedance (Z wind (s)). The change of frequency can be achieved by changing (ω).

[0150] Frequency domain analysis: Plot the frequency response of the wind farm impedance to examine how it changes at different frequencies. This can help identify if there are sudden changes in impedance at certain frequencies that could affect the stability of the system.

[0151] The grid impedance analysis model is as follows:

[0152]

[0153] Among them, (Z grid (s)) is the impedance of the grid, (R grid ) is the DC resistance of the grid, (L grid ) is the inductance of the grid, (τ grid ) is the time constant of the power grid, (C grid ) is the capacitance of the grid;

[0154] When the model is used:

[0155] Impedance calculation: By actually measuring or estimating the grid parameters, the impedance (Z grid (s)).

[0156] Frequency domain analysis: Draw the frequency response diagram of the grid impedance to analyze its characteristics at different frequencies. In particular, the capacitance part of the grid It will have a significant impact on high frequency signals.

[0157] In the frequency domain analysis, different frequencies are selected, and the wind farm impedance analysis model and the power grid impedance analysis model are used to calculate the impedance of the wind farm and the power grid, and a frequency response diagram is drawn to compare the matching degree between the wind farm impedance and the power grid impedance.

[0158] The steps of frequency domain analysis include:

[0159] Impedance calculation: Select different frequencies ω and use the above model to calculate the impedance of the wind farm and the grid. Assume that the DC resistance of the wind farm (R wind =0.1Ω), inductance (L wind =0.01H), time constant (τ wind =0.1s).

[0160] For the power grid, assuming (R grid =0.2Ω), inductance (L grid =0.02H), capacitance (C grid =0.001F), time constant (τ grid =0.2s).

[0161] Plot frequency response: Use the calculated impedance data to plot a frequency response. Analyze the magnitude and phase of the impedance versus frequency to determine the stability of the system.

[0162] Amplitude response: It can help determine the power absorption capacity of the system at different frequencies. Sudden changes in impedance amplitude may cause system resonance.

[0163] Phase response: The change in phase can help determine the phase margin of the system and determine whether the system is stable under frequency changes.

[0164] Impedance matching: Compare the matching degree between the wind farm impedance and the grid impedance. If the impedance of the two differs greatly within the main operating frequency band, it may cause power oscillation or stability problems. Impedance matching can be optimized by adjusting the control strategy of the wind farm or the supporting facilities of the grid.

[0165] S5. Evaluate dynamic response characteristics

[0166] Evaluate the wind farm's ability to respond to disturbances during the grid connection process, and observe the system's response behavior under disturbances by simulating the actual operation of the wind farm and the power grid.

[0167] In this embodiment, when evaluating the response capability of a wind farm to disturbances during the grid connection process, a wind farm dynamic response model and a frequency domain response model are used for evaluation;

[0168] The wind farm dynamic response model is as follows:

[0169]

[0170] Where, (ΔV(t)) is the change in system voltage at time (t), (Pwind(t)) is the power generated by the wind farm at time (t), (Pload(t)) is the load power, (Vbase) is the reference voltage, and (Zwind) is the equivalent impedance of the wind farm;

[0171] The frequency domain response model is as follows:

[0172]

[0173] Where, (H(ω)) is the frequency domain response function, (ω) is the angular frequency, (T wind ) is the time constant of the wind farm system;

[0174] Through frequency domain analysis, we can understand the stability of the system at different frequencies.

[0175] When using,

[0176] Time domain simulation: Use the wind farm dynamic response model to calculate voltage changes under actual wind speed changes and load fluctuations. This can help identify the dynamic response characteristics of the system under disturbances and predict possible voltage deviations.

[0177] Frequency domain analysis: Apply frequency domain response models to perform frequency domain analysis to evaluate the stability of the system at different frequencies. This helps identify possible oscillation modes and dynamic instability issues, ensuring stable operation of the system under various frequency conditions.

[0178] S6. Perform steady-state analysis

[0179] The power balance, power factor, and voltage and frequency stability of the wind farm grid-connected system are evaluated by calculating the system's power flow, load distribution, and the system's voltage and frequency stability to determine the system's stability under steady-state conditions.

[0180] In this embodiment, the system has a built-in power balance model and a voltage stability model to evaluate the stability of the wind farm and the power grid in long-term operation;

[0181] The power balance model is as follows:

[0182] [P wind +P gen =P load +P loss ]

[0183] Among them, (P wind ) is the output power of the wind farm, (P gen ) is the output power of other power generation equipment, (P load ) is the load power demand of the power grid, (P loss ) is the power loss in the system;

[0184] This model is used to ensure that all power input and output from the system are equal under steady-state conditions.

[0185] By collecting the output power of the wind farm, the power of other power generation equipment, load demand and system loss data and substituting them into the model, it is possible to verify whether the system has achieved power balance and thus determine whether the system remains stable under steady-state conditions. If the power is unbalanced, it may be necessary to adjust the output of the wind farm or the configuration of other power generation equipment to achieve balance.

[0186] The voltage stability model is as follows:

[0187]

[0188] Among them, (V bus ) is the grid bus voltage, (P load ) and (Q load ) are the active and reactive power of the load, respectively, (Z bus ) is the impedance of the grid bus.

[0189] The model is used to assess whether the bus voltage is within the expected range, thereby ensuring the voltage stability of the power grid.

[0190] In steady-state analysis, the active and reactive power of the load and the grid impedance value are substituted into the model to calculate the voltage of the grid bus. If the calculated voltage deviates from the expected range, it may cause voltage instability, requiring grid regulation or load distribution adjustment.

[0191] S7. Evaluate the impact of grid connection on the power grid

[0192] Evaluate the impact of wind farm connection on the power grid, determine whether it will have a negative impact on the stability of the power grid, analyze the voltage fluctuations, frequency changes and system harmonics of the power grid, and use power system simulation tools to simulate and analyze the power grid after connection.

[0193] like Figure 3 As shown, in this embodiment, when performing simulation analysis, the following process is specifically included:

[0194] Build simulation models, and build wind farm models and power grid models in power system simulation tools DlgSILENT PowerFactory, PSS / E, and MATLAB / Simulink;

[0195] Set up simulation scenarios to simulate the grid-connected operation of wind farms under normal wind speed and load conditions, and set up different fault and disturbance scenarios, such as sudden changes in wind speed, sudden increases and decreases in load, and grid faults, to observe the response of wind farms after grid connection;

[0196] Perform simulation analysis to conduct voltage fluctuation analysis, frequency variation analysis, and harmonic analysis.

[0197] S8. Design control strategy

[0198] The control strategy includes wind turbine power control, converter current control, and system voltage and frequency regulation. By designing control algorithms such as PID control and fuzzy control, the stability and performance of the system are improved, and multiple simulation tests are performed to determine the optimal control parameters and strategies.

[0199] like Figure 2 As shown, in this embodiment, the control strategy:

[0200] Wind turbine power control, power regulation algorithms based on wind speed prediction and grid demand, such as maximum power point tracking (MPPT) combined with power limiting strategies, ensure that wind turbine output matches grid demand;

[0201] Current control of the converter, design the current control loop of the converter, including dq axis current control, using PI controller to quickly respond to grid current demand;

[0202] Voltage and frequency regulation, designing active regulation strategies for voltage and frequency, such as using droop control or virtual synchronous generator (VSG) technology, simulating the characteristics of conventional generators.

[0203] Embodiment 2:

[0204] See also Figure 4 A wind farm grid-connected stability rapid assessment system based on an impedance model is constructed based on the wind farm grid-connected stability rapid assessment method based on an impedance model described in Example 1, and includes a data collection module, a model building module, an assessment index selection module, an impedance matching analysis module, a dynamic response assessment module, a steady-state analysis module, a power grid impact assessment module, and a control strategy design module.

[0205] The data collection module receives data from the wind farm and the power grid.

[0206] The model building module builds the physical model of the wind farm grid-connected system and the impedance model of the wind farm and the power grid.

[0207] The evaluation index selection module selects the evaluation index based on user needs and wind farm characteristics.

[0208] The impedance matching analysis module outputs the impedance matching analysis results based on the impedance model of the wind farm and the power grid.

[0209] The dynamic response assessment module is used to evaluate the wind farm’s ability to respond to disturbances during the grid connection process.

[0210] Steady-state analysis module, for performing steady-state analysis of the system.

[0211] The grid impact assessment module evaluates the impact of wind farm connection on the grid, including grid voltage fluctuations, frequency changes and harmonics.

[0212] The control strategy design module designs the control strategy of the wind farm, including the power control of the wind turbine, the current control of the converter, and the voltage and frequency regulation of the system.

[0213] In this embodiment, the system further includes a data management module for recording all evaluation data, simulation results and test results and performing data backup, and generating a report based on the evaluation data, simulation results and test results.

[0214] By recording all evaluation data, simulation results, and test results, detailed analysis and summary can be performed to identify potential problems and improvement points in the system, providing a basis for future optimization. In addition, the report generated by the recorded results can be shared with relevant departments or agencies for further review and verification.

[0215] At the same time, as the technology and operating environment of wind farms and power grids continue to develop, the evaluation methods need to be continuously optimized and updated. The system regularly updates the evaluation methods, models, and control strategies based on new technological advances and operating experience to adapt to changing conditions and requirements. Continuous optimization methods include improving the accuracy of the model, introducing new control technologies, and updating evaluation indicators. Ensure that the evaluation methods can keep pace with the times and maintain their effectiveness and reliability in practical applications.

[0216] The beneficial effects of the present invention are:

[0217] This impedance model-based wind farm grid-connected stability rapid assessment method and system achieves a comprehensive and rapid assessment of wind farm grid-connected stability by constructing an accurate wind farm and grid impedance model and combining multiple assessment indicators and control strategies. This method not only improves the accuracy and real-time performance of the assessment, but also effectively identifies and solves potential stability problems, providing strong support for the safe and efficient grid connection of wind farms. At the same time, by designing a reasonable control strategy, the stability and performance of the wind farm grid-connected system are further improved, promoting the large-scale development and utilization of wind power resources.

[0218] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0219] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for rapid assessment of wind farm grid-connected stability based on impedance model, characterized in that: The following steps are involved: S1. Establish the physical model of the wind farm grid-connected system Collect data on the wind farm grid-connected system, analyze the overall structure and parameters of the wind farm grid-connected system, and build a physical model of the wind farm grid-connected system. The physical model shows the interaction between the various components in the system and provides a framework for subsequent impedance modeling; S2. Establish impedance model of wind farm and power grid The impedance model of the wind farm includes the impedance of the wind turbine system, the impedance of the converter and the total impedance of the wind farm; the impedance model of the power grid includes the impedance of the transmission line, the impedance of the transformer and the load impedance of the power grid. By calculating the impedance of the wind farm and the power grid, the complex impedance matrix of the wind farm grid-connected system is obtained. S3. Choose appropriate evaluation metrics Determine the evaluation indicators to measure the stability of the wind farm grid-connected system, including voltage stability, frequency stability, and power factor; when selecting the evaluation indicators, consider the characteristics of the wind farm and the requirements of the power grid, such as selecting indicators of voltage transient response, frequency response, and power fluctuation for analysis; S4. Perform impedance matching analysis By comparing the impedance of the wind farm and the grid, the stability of the system is judged. Impedance matching analysis is used to identify potential stability issues and ensure that the system remains stable in all operating frequency ranges. S5. Evaluate dynamic response characteristics Evaluate the wind farm's ability to respond to disturbances during the grid connection process, and observe the system's response behavior under disturbances by simulating the actual operation of the wind farm and the grid; S6. Perform steady-state analysis Evaluate the power balance, power factor, and voltage and frequency stability of the wind farm grid-connected system by calculating the system's power flow, load distribution, and the system's voltage and frequency stability to determine the system's stability under steady-state conditions; S7. Evaluate the impact of grid connection on the power grid Evaluate the impact of wind farm connection on the power grid, determine whether it will have a negative impact on the stability of the power grid, analyze the voltage fluctuation, frequency change and system harmonics of the power grid, and use power system simulation tools to simulate and analyze the power grid after connection; S8. Design control strategy The control strategy includes wind turbine power control, converter current control, and system voltage and frequency regulation. By designing control algorithms such as PID control and fuzzy control, the stability and performance of the system are improved, and multiple simulation tests are performed to determine the optimal control parameters and strategies.

2. A method for rapid assessment of wind farm grid connection stability based on impedance model according to claim 1, characterized in that: In step S1, the data of the wind farm grid-connected system includes wind speed and direction data, power generation data, wind turbine operation data, power grid data, converter and electrical equipment data, environmental factor data, and fault and abnormality data.

3. The method for rapid assessment of wind farm grid connection stability based on impedance model according to claim 1, characterized in that: In step S2, when establishing the impedance model of the wind farm: Impedance Z of the fan system wind It is expressed as: Z wind =R wind +jX wind Among them, R wind is the resistance of the fan, X wind is the reactance of the fan; The impedance Z of the converter converter It is expressed as: Z converter =R converter +jX converter Among them, R converter is the resistance of the converter, X converter is the reactance of the converter; The total impedance of the wind farm is Z total The parallel impedance of the fan and converter is calculated as follows: When establishing the impedance model of the power grid: The impedance of the transmission line Z line It is expressed as: Z line =R line +jX line Among them, R line is the resistance of the transmission line, X line is the reactance of the transmission line; The impedance of the transformer is Z transformer It is expressed as: Z transformer =R transformer +jX transformer Among them, R transfirner is the resistance of the transformer, X transformer is the reactance of the transformer; The load impedance of the power grid is Z load It is expressed as: Z load =R load +jX load The total impedance of the power grid is Z grid It is expressed as: WITH grid =Z line +Z transformer +Z load When calculating the complex impedance matrix of the wind farm grid-connected system: Z system is the complex impedance matrix of the wind farm and the power grid, then the matrix is ​​expressed as: Among them, Z interface is the impedance of the interface between the wind farm and the grid.

4. The method for rapid assessment of wind farm grid connection stability based on impedance model according to claim 1, characterized in that: In the step S4, a wind farm impedance analysis model and a power grid impedance analysis model are constructed, and frequency domain analysis is performed to check the impedance characteristics of the system at different frequencies; The wind farm impedance analysis model is as follows: Among them, (Z wind (s)) is the impedance of the wind farm, where (s) is the complex frequency variable in the Laplace transform, (R wind ) is the DC resistance of the wind farm, (L wind ) is the inductance of the wind farm, (τ wind ) is the time constant of the wind farm; The grid impedance analysis model is as follows: Among them, (Z grid (s)) is the impedance of the grid, (R grid ) is the DC resistance of the grid, (L grid ) is the inductance of the grid, (τ grid ) is the time constant of the power grid, (C grid ) is the capacitance of the grid; In the frequency domain analysis, different frequencies are selected, and the wind farm impedance analysis model and the power grid impedance analysis model are used to calculate the impedance of the wind farm and the power grid, and a frequency response diagram is drawn to compare the matching degree between the wind farm impedance and the power grid impedance.

5. The method for rapid assessment of wind farm grid connection stability based on impedance model according to claim 1, characterized in that: In step S5, when evaluating the response capability of the wind farm to disturbances during the grid connection process, the wind farm dynamic response model and the frequency domain response model are used for evaluation; The wind farm dynamic response model is as follows: Where, (ΔV(t)) is the change in system voltage at time (t), (Pwind(t)) is the power generated by the wind farm at time (t), (Pload(t)) is the load power, (Vbase) is the reference voltage, and (Zwind) is the equivalent impedance of the wind farm; The frequency domain response model is as follows: Where, (H(ω)) is the frequency domain response function, (ω) is the angular frequency, (T wind ) is the time constant of the wind farm system; Through frequency domain analysis, we can understand the stability of the system at different frequencies.

6. The method for rapid assessment of wind farm grid connection stability based on impedance model according to claim 1, characterized in that: In step S6, the system has a built-in power balance model and a voltage stability model to evaluate the stability of the wind farm and the power grid in long-term operation; The power balance model is as follows: [P wind +P gen =P load +P loss ] Among them, (P wind ) is the output power of the wind farm, (P gen ) is the output power of other power generation equipment, (P load ) is the load power demand of the power grid, (P loss ) is the power loss in the system; The voltage stability model is as follows: Among them, (V bus ) is the grid bus voltage, (P load ) and (Q load ) are the active and reactive power of the load, respectively, (Z bus ) is the impedance of the grid bus.

7. The method for rapid assessment of wind farm grid connection stability based on impedance model according to claim 1, characterized in that: In the step S7, when performing simulation analysis, the following process is specifically included: Build simulation models, and build wind farm models and power grid models in power system simulation tools DIgSILENT PowerFactory, PSS / E, and MATLAB / Simulink; Set up simulation scenarios to simulate the grid-connected operation of wind farms under normal wind speed and load conditions, and set up different fault and disturbance scenarios, such as sudden changes in wind speed, sudden increases and decreases in load, and grid faults, to observe the response of wind farms after grid connection; Perform simulation analysis to conduct voltage fluctuation analysis, frequency variation analysis, and harmonic analysis.

8. The method for rapid assessment of wind farm grid connection stability based on impedance model according to claim 1, characterized in that: In step S8, in the control strategy: Wind turbine power control, power regulation algorithms based on wind speed prediction and grid demand, such as maximum power point tracking (MPPT) combined with power limiting strategies, ensure that wind turbine output matches grid demand; Current control of the converter, design the current control loop of the converter, including dq axis current control, using PI controller to quickly respond to grid current demand; Voltage and frequency regulation, designing active regulation strategies for voltage and frequency, such as using droop control or virtual synchronous generator (VSG) technology, simulating the characteristics of conventional generators.

9. A wind farm grid-connected stability rapid assessment system based on an impedance model, constructed based on the wind farm grid-connected stability rapid assessment method based on an impedance model according to any one of claims 1 to 8, characterized in that: It includes data collection module, model building module, evaluation index selection module, impedance matching analysis module, dynamic response evaluation module, steady-state analysis module, power grid impact evaluation module and control strategy design module; A data collection module receives data from wind farms and power grids; Model building module, which builds the physical model of the wind farm grid-connected system and the impedance model of the wind farm and the power grid; Evaluation index selection module, which selects evaluation indexes based on user needs and wind farm characteristics; Impedance matching analysis module, based on the impedance model of wind farm and power grid, outputs impedance matching analysis results; Dynamic response assessment module, which evaluates the wind farm’s ability to respond to disturbances during the grid connection process; Steady-state analysis module, to perform steady-state analysis of the system; The grid impact assessment module evaluates the impact of wind farm grid connection on the grid, including grid voltage fluctuations, frequency changes and harmonics; The control strategy design module designs the control strategy of the wind farm, including the power control of the wind turbine, the current control of the converter, and the voltage and frequency regulation of the system.

10. A wind farm grid-connected stability rapid assessment system based on impedance model according to claim 9, characterized in that: The system also includes a data management module for recording all evaluation data, simulation results and test results and performing data backup, and generating reports based on the evaluation data, simulation results and test results.

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