A dynamic equivalent modeling method for renewable energy grid-connected systems

Abstract

The present invention discloses a method for dynamic equivalent modeling of a new energy grid-connected system, and relates to the technical field of power systems. The steps are: under different operating modes, measure the input admittance of the new energy grid-connected system, and collect the steady-state current value of the PCC point; use the transfer function identification method and the function fitting method to fit the transfer function and its various-order coefficients of the measured admittance in turn; on this basis, calculate the equivalent admittance and small signal component of the system according to the dynamic characteristics of the phase-locked loop; at the same time, use the function fitting method to fit the steady-state current of the PCC point; finally, superimpose the fitted steady-state component and the small signal component to obtain the reference output of the controlled current source in the equivalent model, and realize the dynamic equivalent modeling of the new energy grid-connected system under variable working conditions. The present invention can perform time domain simulation while maintaining frequency domain consistency, does not rely on the specific structural parameters of the original system, speeds up the time domain simulation speed of the system, and can also be applied to the stability analysis and research of broadband oscillations.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a dynamic equivalent modeling method for a new energy grid-connected system. Background Art

[0002] As a renewable energy source with low cost, abundant reserves and high utilization rate, wind power has become the new energy power generation technology with the largest increase in installed capacity in recent years, and has been developed and utilized on a large scale worldwide. However, in recent years, broadband oscillation events in wind power grid-connected systems have often occurred. The propagation path and inducing mechanism of such oscillations have not yet been clarified, which is an important factor threatening the safe and stable operation of new energy power systems. In order to study the problem of broadband oscillation, it is necessary to construct a wind power grid-connected system model for theoretical analysis and simulation calculations. Due to the large scale and high order of actual wind power systems, detailed modeling of each device will lead to the problem of dimensionality disaster. Therefore, an equivalent model is usually used to study the dynamic characteristics of wind power grid-connected systems.

[0003] Aggregation method is a commonly used dynamic equivalent modeling method for renewable energy grid-connected systems. It reduces the number of target units by equating the wind turbines in the entire renewable energy grid-connected system to a single or multiple units, thereby simplifying the modeling analysis. However, in the existing literature on aggregation method, most of them only focus on the consistency of the time domain response of the active and reactive output of renewable energy grid-connected systems before and after the equivalent. It is difficult to guarantee whether such modeling methods can characterize the multi-scale dynamic interaction characteristics of large-scale wind power grid-connected systems and conduct effective analysis of broadband oscillations. Summary of the invention

[0004] The object of the present invention is to provide a dynamic equivalent modeling method for a new energy grid-connected system. The proposed method equates the new energy grid-connected system to a current source obtained by superimposing a steady-state component and a small signal component. The input admittance matrix of the new energy grid-connected system under different operating modes is obtained by adopting an admittance measurement method based on a dq coordinate system, and the transfer function identification method is used to fit the measured admittance under each operating mode. The relationship between each order coefficient of the admittance transfer function and the operating point of the new energy grid-connected system is obtained based on the function fitting method, and then the equivalent admittance matrix of the original system is calculated based on the dynamic response characteristics of the phase-locked loop. At the same time, under different operating modes of the new energy grid-connected system, the steady-state current of the PCC point is collected and the relationship between it and the operating point of the new energy grid-connected system is fitted. Then, the voltage of the PCC point in the three-phase stationary coordinate system is collected for dq coordinate transformation, and the corresponding voltage small signal components are obtained after subtracting the corresponding voltage steady-state components. Further, the current small signal component in the dq control coordinate system is calculated based on the equivalent admittance of the new energy grid-connected system, and the current component in the dq control coordinate system can be obtained by superimposing the fitted current steady-state components. Finally, the current component is transformed from the dq control coordinate system to the three-phase stationary coordinate system as the reference value output of the controlled current source of the equivalent model, realizing the dynamic equivalent modeling of the new energy grid-connected system under variable operating conditions, and providing a basis for the stability analysis and simulation calculation of wide-band oscillations.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A dynamic equivalent modeling method for a new energy grid-connected system, characterized in that the new energy grid-connected system is equivalent to a three-phase controlled current source, and the equivalent modeling method comprises the following steps:

[0007] Step S1: Under different operation modes of the new energy grid-connected system, the admittance measurement method based on the dq coordinate system is used to obtain the input admittance matrix of the new energy grid-connected system.

[0008]

[0009] Wherein, k and i represent the kth operation mode and the ith measurement frequency respectively;

[0010] Step S2: Under each operation mode of the new energy grid-connected system, use the transfer function identification method to identify all the measured frequencies obtained in step S1. Perform transfer function fitting and obtain

[0011]

[0012] Step S3: Take out the The coefficients of each order of each admittance in the matrix are used to obtain the relationship between each coefficient and the operating point of the new energy grid-connected system using the function fitting method, and the final admittance transfer function fitting result of the new energy grid-connected system is obtained. and

[0013] Step S4: Based on the dynamic response characteristics of the phase-locked loop, and Compensation is performed to obtain the equivalent admittance matrix Y of the new energy grid-connected system Eq ;

[0014] Step S5: Under different operation modes of the new energy grid-connected system, collect the component I of the steady-state current at the PCC point in the dq coordinate system of the AC system gd ,I gq ;

[0015] Step S6: Use a function fitting method to calculate the steady-state current component I in step S5. gd ,I gq The relationship between the operating point of the renewable energy grid-connected system is fitted to obtain the fitted steady-state current component and

[0016] Step S7: Collect the voltage u of the PCC point in the three-phase stationary coordinate system pa 、u pb 、u pc And perform dq coordinate transformation to obtain the corresponding components in the dq control coordinate system and

[0017]

[0018] Where θ is the phase angle provided by the phase-locked loop;

[0019] Step S8: Using the data obtained in step S7 and Subtract the steady-state component U of the PCC voltage in the infinite power grid dq coordinate system pd and U pq , and the corresponding voltage small signal component is obtained and Right now:

[0020]

[0021] Step S9: Based on the voltage small signal component in step S8 and the equivalent admittance matrix Y in step S4 Eq , calculate the current small signal component in the dq control coordinate system and

[0022]

[0023] Step S10: Current small signal component in step S9 and On this basis, the current steady-state components obtained by step S5 are superimposed respectively. and Get the current component in the dq control coordinate system and

[0024]

[0025] Step S11: Based on the phase angle θ provided by the phase-locked loop, the current and Transform the dq control coordinate system to the three-phase stationary coordinate system and obtain i ga 、i gb and i gc , as the reference value of the three-phase controlled current source of the equivalent model of the new energy grid-connected system:

[0026]

[0027] Furthermore, in the k-th operation mode in step S1, the admittance measurement method based on the dq coordinate system at the i-th measurement frequency is:

[0028] Step S11: Given the system phase angle in the simulation model, keep the q-axis current disturbance at 0, and apply a frequency of f to the d-axis current. i The sinusoidal disturbance signal is converted into a three-phase current disturbance by coordinate transformation;

[0029] Step S12: injecting the three-phase current disturbance in step S11 into the PCC point through a controlled current source, and collecting the voltage and current at the PCC point for dq coordinate transformation;

[0030] Step S13: Separate the frequency f using parameter identification algorithm i The voltage and current are obtained and

[0031] Step S14: in the simulation model, a system phase angle is given, the d-axis current disturbance is kept at 0, a sinusoidal disturbance signal of a specific frequency is applied to the q-axis current, and the signal is converted into a three-phase current disturbance using an abc coordinate transformation;

[0032] Step S15: Repeat the process from step S12 to step S13 to obtain and

[0033] Step S16: Using the voltage and current values ​​in step S13 and step S15, calculate the frequency f i The admittance matrix of the dq coordinate system under

[0034]

[0035] Furthermore, the transfer function fitting process in step S2 is:

[0036] Step S21: taking out all frequency points within the measurement frequency range and the corresponding dq coordinate system measurement admittances, and using them as frequency and response inputs of the transfer function identification algorithm respectively;

[0037] Step S22: Set the number of zeros and poles of the fitting transfer function, and use the transfer function identification algorithm to obtain the fitted admittance transfer function:

[0038]

[0039] In the formula, y(s) represents or or or b m , b m-1 , b m-2 ,…,b1,b0,a n 、a n-1 、a n-2 , …, a1, a0 are all real constants; m and n are the number of zeros and poles of the set fitting transfer function respectively;

[0040] Step S23: adjusting the number of zero poles of the fitting, and taking the transfer function with a fitting degree greater than the set value as the transfer function of the final dq coordinate system measurement admittance.

[0041] Furthermore, the function fitting step of each order coefficient of the admittance transfer function with respect to the operating point in step S3 is:

[0042] Step S31: extracting characteristic parameters of each operating point and coefficients of specific orders of the numerator or denominator of the measured admittance at each operating point;

[0043] Step S32: taking the characteristic parameter as the independent variable and the coefficient of the specific order of admittance as the dependent variable, setting the order of each variable, and inputting the function fitting algorithm to fit the relationship between the variables;

[0044] Step S33: Adjust the order of each variable, and take the fitting function with the lowest order of independent variables among the results whose fitting degree is greater than the set value as the final result.

[0045] Furthermore, in step S4, the equivalent admittance matrix Y of the new energy grid-connected system Eq The calculation method is:

[0046]

[0047] In the formula, G pll (s) is the transfer function of the phase-locked loop control system;

[0048] Furthermore, in step S6, the steady-state current component I gd ,I gq The function fitting method is:

[0049] Step S61: Take out the characteristic parameters of each operating point and the PCC point steady-state current component I at each operating point in step S4 gd ,I gq ;

[0050] Step S62: Taking the characteristic parameter as an independent variable, I gd or I gq For the dependent variable, set the fitting times of each variable, and input the function fitting algorithm to fit the relationship between variables;

[0051] Step S63: Adjust the fitting times of the respective variables, and take the fitting function with the lowest number of independent variables among the results with a fitting degree greater than the set value to describe the relationship between the steady-state component of the PCC point current and the operating point.

[0052] Furthermore, the input signal of the phase-locked loop control system in step S7 is the voltage u of the PCC point in the three-phase stationary coordinate system. pa 、u pb 、u pc

[0053] Beneficial effects of the present invention:

[0054] The dynamic equivalent modeling method of the new energy grid-connected system based on variable operating condition admittance fitting of the present invention is a time domain simulation method based only on system measurement data. It does not rely on the specific structural parameters of the original system and does not need to solve a group of differential algebraic equations reflecting the dynamic characteristics of the power system, thereby accelerating the time domain simulation speed of the system. At the same time, since the method aims at the consistency of the admittance curve of the new energy grid-connected system before and after the equivalent, it also ensures the frequency domain consistency that is closely related to the wide-band oscillation stability, thereby ensuring the correctness of the equivalent model of the new energy grid-connected system for time domain stability analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The present invention will be further described below in conjunction with the accompanying drawings.

[0056] Figure 1 It is a flow chart of the present invention;

[0057] Figure 2 It is a comparison diagram of the measured admittance curves before and after the equalization of the new energy grid-connected system in the first embodiment of the present invention;

[0058] Figure 3 It is a comparison diagram of dynamic characteristic curves before and after the equalization of the new energy grid-connected system in the first embodiment of the present invention;

[0059] Figure 4 is a comparison diagram of the measured admittance curves before and after the equalization of the new energy grid-connected system in the second embodiment of the present invention;

[0060] Figure 5 It is a comparison diagram of dynamic characteristic curves before and after the equalization of the new energy grid-connected system in the second embodiment of the present invention. DETAILED DESCRIPTION

[0061] The following will be combined with the drawings in 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.

[0062] This embodiment adopts a new energy grid-connected system model in which a single direct-drive wind turbine is connected to an infinite power grid, and performs dynamic equivalent modeling of the wind farm based on the PCC point steady-state current and wind farm input admittance obtained by function fitting, such as Figure 1 The equivalent model of the wind farm is a current source obtained by superimposing a steady-state component and a small signal component. The specific equivalent process includes the following steps:

[0063] Step S1: Under different operation modes of the wind farm, the admittance measurement method based on the dq coordinate system is used to obtain the input admittance matrix of the wind farm.

[0064]

[0065] Where k and i represent the kth operation mode and the ith measurement frequency respectively. The specific steps of wind farm input admittance measurement are as follows:

[0066] Step S11: Given the system phase angle in the simulation model, keep the q-axis current disturbance at 0, and apply a frequency of f to the d-axis current. i The sinusoidal disturbance signal is converted into a three-phase current disturbance using abc coordinate transformation;

[0067] Step S12: injecting the three-phase current disturbance in step S11 into the PCC point through a controlled current source, and collecting the voltage and current at the PCC point for dq coordinate transformation;

[0068] Step S13: Separate the frequency f using parameter identification algorithm i The voltage and current are obtained and

[0069] Step S14: in the simulation model, a system phase angle is given, the d-axis current disturbance is kept at 0, a sinusoidal disturbance signal of a specific frequency is applied to the q-axis current, and the signal is converted into a three-phase current disturbance using an abc coordinate transformation;

[0070] Step S15: Repeat the process from step S12 to step S13 to obtain and (i);

[0071] Step S16: Using the voltage and current values ​​in step S13 and step S15, calculate the frequency f i The admittance matrix of the dq coordinate system under

[0072]

[0073] Step S2: Under each operation mode of the wind farm, use the transfer function identification method to identify all the measured frequencies obtained in step S1. Perform transfer function fitting and obtain

[0074]

[0075] The specific steps are:

[0076] Step S21: taking out all frequency points within the measurement frequency range and the corresponding dq coordinate system measurement admittance, and using them as frequency and response inputs of the system identification toolbox in Matlab software respectively;

[0077] Step S22: Set the number of zeros and poles of the fitting transfer function, and use the transfer function fitting module in the system identification toolbox to fit the admittance transfer function:

[0078]

[0079] In the formula, y(s) represents or or or b m , b m-1 , b m-2 ,…,b1,b0,a n 、a n-1 、a n-2, …, a1, a0 are all real constants; m and n are the number of zeros and poles of the set fitting transfer function respectively;

[0080] Step S23: Calculate the fit of the transfer function according to the tfeSt function, adjust the number of zero poles of the fit, and take the transfer function with a fit greater than 95% as the final transfer function of the dq coordinate system measurement admittance.

[0081] Step S3: Take out the The coefficients of each order of each admittance in the matrix are used to obtain the relationship between each coefficient and the operating point of the wind farm using the function fitting method. The specific steps are as follows:

[0082] Step S31: Get the wind speed v(k) and q-axis current given values ​​at each operating point and the coefficients of specific orders of the numerator or denominator of the measured admittance at each operating point, such as b m (k), where k = 1, 2, ..., K, represents the kth operating point;

[0083] Step S32: wind speed v(k) and As an independent variable, the coefficient b of a specific order of admittance m (k) as the dependent variable, set the times of each variable, and input the fit function in Matlab software to perform binary function fitting;

[0084] Step S33: Using the goodness of fit R 2 Calculate the fit, adjust the times of each variable, and take the fitting function with the lowest times of independent variables among the results with a fit greater than 95% as the final result. 2 The calculation formula is:

[0085]

[0086] In the formula, X i is the actual value; x i is the fitted value; For X i The average value of .

[0087] Step S4: Based on the dynamic response characteristics of the phase-locked loop, Y * Re_qd (s) and Compensation is performed to obtain the equivalent admittance matrix Y of the new energy grid-connected system Eq , where Y Eq The calculation method is:

[0088]

[0089] In the formula, G pll(s) is the transfer function of the phase-locked loop control system. The transfer function of the phase-locked loop used in the embodiment is:

[0090]

[0091] Among them, k p and k i are the proportional and integral coefficients of the phase-locked loop respectively.

[0092] Step S5: Under different operation modes of the wind farm, collect the component I of the steady-state current at the PCC point in the dq coordinate system of the AC system gd ,I gq .

[0093] Step S6: Use a function fitting method to calculate the steady-state current component I in step S5. gd ,I gq The relationship between the wind farm operation point is fitted to obtain the fitted steady-state current component and Among them, the steady-state current component I gd ,I gq The function fitting method is:

[0094] Step S61: Get the wind speed v and q-axis current given values ​​at each operating point And the PCC point steady-state current component I at each operating point in step S4 gd ,I gq ;

[0095] Step S62: Using wind speed v and is the independent variable, I gd or I gq As the dependent variable, set wind speed v and The highest fitting number is input into the fit function in Matlab software to perform steady-state component I gd and I gq The binary function fitting of ;

[0096] Step S63: Using the goodness of fit R 2 Calculate the fitting degree, adjust the fitting times of each variable, and take the fitting function with the lowest number of independent variables among the results with a fitting degree greater than 95% to describe the relationship between the steady-state component of the PCC point current and the operating point, so as to obtain the fitted steady-state current component and

[0097] Step S7: Collect the voltage u of the PCC point in the three-phase stationary coordinate system pa 、u pb 、u pc And perform dq coordinate transformation to obtain the corresponding components in the dq control coordinate system and

[0098]

[0099] Where θ is the phase angle provided by the phase-locked loop, and the input signal of the phase-locked loop is the voltage u at the PCC point in the three-phase stationary coordinate system. pa 、u pb 、u pc .

[0100] Step S8: Using the and Subtract the steady-state component U of the PCC voltage in the infinite power grid dq coordinate system pd and U pq , and the corresponding voltage small signal component is obtained and Right now:

[0101]

[0102] Step S9: Calculate the current small signal component in the dq control coordinate system according to the voltage small signal component in step S7 and

[0103]

[0104] Step S10: Current small signal component in step S8 and On this basis, the current steady-state components obtained by step S5 are superimposed respectively. and Get the current component in the dq control coordinate system and

[0105]

[0106] Step S11: Based on the phase angle θ provided by the phase-locked loop, the current and Transform the dq control coordinate system to the three-phase stationary abc coordinate system and obtain i ga 、i gb and i gc , as the reference value of the three-phase controlled current source of the wind farm equivalent model:

[0107]

[0108] The method is further described below in conjunction with the results of a specific embodiment. Based on the simulation system of this embodiment, Y qd Always 0, so Y is not considered in the embodimentqd Correlated fits and isovalues.

[0109] Embodiment 1: Wind speed v = 4.5 m / s, Comparison of wind farm equivalent results under different conditions

[0110] (1) Comparison of measured admittance curves before and after wind farm equalization

[0111] Figure 2 Given the wind speed v = 4.5m / s, The original system admittance curve of the wind farm under the condition and the equivalent model admittance curve based on the phase-locked loop are compared. It can be seen that the measured equivalent system admittance curve is consistent with the original system admittance curve of the wind farm, which verifies that the wind farm equivalent modeling method proposed in the present invention can maintain the frequency domain consistency of the wind farm before and after the equivalent.

[0112] (2) Comparison of dynamic characteristic curves before and after wind farm equalization

[0113] In the second second of the time domain simulation, a pulse disturbance is added to the PCC point voltage in the system before and after the equivalent value, and the wind speed v = 4.5m / s, The dynamic characteristic curves of the wind farm before and after equalization under the condition are as follows: Figure 3 It can be seen that the dynamic process of the wind farm before and after the equalization is basically the same, which verifies the correctness of this method for the dynamic equalization of the wind farm and can be used to judge the time domain stability of the wind power system.

[0114] (3) Comparison of simulation time before and after wind farm equalization

[0115] In the dynamic characteristic curve comparison test of the wind farm before and after the equivalent value in Example 1 (2), the original system simulation took 7.711023 seconds, and the equivalent system simulation took 5.132814 seconds. It can be seen that the system simulation time after the equivalent value is shortened, which verifies that this method can improve the time domain simulation speed.

[0116] Embodiment 2: Wind speed v = 6m / s, Comparison of wind farm equivalent results under different conditions

[0117] (1) Comparison of measured admittance curves before and after wind farm equalization

[0118] Figure 4 Given the wind speed v = 6m / s, The original system admittance curve of the wind farm under the condition and the equivalent model admittance curve based on the phase-locked loop are compared. It can be seen that the measured equivalent system admittance curve is consistent with the original system admittance curve of the wind farm, which verifies that the wind farm equivalent modeling method proposed in the present invention can maintain the frequency domain consistency of the wind farm before and after the equivalent.

[0119] (2) Comparison of dynamic characteristic curves before and after wind farm equalization

[0120] In the second second of the time domain simulation, a pulse disturbance is added to the PCC point voltage in the system before and after the equivalent value, and the wind speed v = 6m / s, The dynamic characteristic curves of the wind farm before and after equalization under the condition are as follows: Figure 5 It can be seen that the dynamic process of the wind farm before and after the equalization is basically the same, which verifies the correctness of this method for the dynamic equalization of the wind farm and can be used to judge the time domain stability of the wind power system.

[0121] (3) Comparison of simulation time before and after wind farm equalization

[0122] In the dynamic characteristic curve comparison test of the wind farm before and after equalization in Example 2 (2), the original system simulation took 7.533677 seconds, and the equivalent system simulation took 4.858612 seconds. It can be seen that the system simulation time after equalization is shortened, which verifies that this method can improve the time domain simulation speed.

[0123] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A dynamic equivalent modeling method for a new energy grid-connected system, characterized in that: The new energy grid-connected system is equivalent to a three-phase controlled current source, and the equivalent modeling method includes the following steps: Step S1: Under different operation modes of the renewable energy grid-connected system, the admittance measurement method based on the dq coordinate system is used to obtain the input admittance matrix of the renewable energy grid-connected system. Wherein, k and i represent the kth operation mode and the ith measurement frequency respectively; Step S2: Under each operation mode of the new energy grid-connected system, use the transfer function identification method to identify all the measured frequencies obtained in step S1. Perform transfer function fitting and obtain Step S3: Take out the The coefficients of each order of each admittance in the matrix are used to obtain the relationship between each coefficient and the operating point of the new energy grid-connected system using the function fitting method, and the final admittance transfer function fitting result of the new energy grid-connected system is obtained. and Step S4: Based on the dynamic response characteristics of the phase-locked loop, and Compensation is performed to obtain the equivalent admittance matrix Y of the new energy grid-connected system Eq ; Step S5: Under different operation modes of the new energy grid-connected system, collect the component I of the steady-state current at the PCC point in the dq coordinate system of the AC system gd ,I gq ; Step S6: Use the function fitting method to calculate the steady-state current component I in step S5 gd ,I gq The relationship between the operating point of the renewable energy grid-connected system is fitted to obtain the fitted steady-state current component and Step S7: Collect the voltage u of the PCC point in the three-phase stationary coordinate system pa 、u pb 、u pc And perform dq coordinate transformation to obtain the corresponding components in the dq control coordinate system and Where θ is the phase angle provided by the phase-locked loop; Step S8: Using the data obtained in step S7 and Subtract the steady-state component U of the PCC voltage in the infinite power grid dq coordinate system pd and U pq , and the corresponding voltage small signal component is obtained and Right now: Step S9: Based on the voltage small signal component in step S8 and the equivalent admittance matrix Y in step S4 Eq , calculate the current small signal component in the dq control coordinate system and Step S10: The current small signal component in step S9 and On this basis, the current steady-state components obtained by step S5 are superimposed respectively. and Get the current component in the dq control coordinate system and Step S11: Based on the phase angle θ provided by the phase-locked loop, the current and Transform the dq control coordinate system to the three-phase stationary coordinate system and obtain i ga 、i gb and i gc , as the reference value of the three-phase controlled current source of the equivalent model of the new energy grid-connected system: The transfer function fitting process in step S2 is: Step S21: taking out all frequency points within the measurement frequency range and the corresponding dq coordinate system measurement admittances, and using them as frequency and response inputs of the transfer function identification algorithm respectively; Step S22: Set the number of zeros and poles of the fitting transfer function, and use the transfer function identification algorithm to obtain the fitted admittance transfer function: In the formula, y(s) represents or or or b m 、b m-1 、b m-2 ,…,b1,b0,a n 、a n-1 、a n-2 , …, a1, a0 are all real constants; m and n are the number of zeros and poles of the set fitting transfer function respectively; Step S23: adjusting the number of zero poles of the fitting, and taking the transfer function with a fitting degree greater than the set value as the transfer function of the final dq coordinate system measurement admittance; The function fitting steps of each order coefficient of the admittance transfer function with respect to the operating point in step S3 are: Step S31: extracting characteristic parameters of each operating point and coefficients of specific orders of the numerator or denominator of the measured admittance at each operating point; Step S32: taking the characteristic parameter as the independent variable and the coefficient of the specific order of admittance as the dependent variable, setting the order of each variable, and inputting the function fitting algorithm to fit the relationship between the variables; Step S33: adjusting the number of independent variables, and taking the fitting function with the lowest number of independent variables among the results whose fitting degree is greater than the set value as the final result; The equivalent admittance matrix Y of the new energy grid-connected system in step S4 Eq The calculation method is: In the formula, G pll (s) is the transfer function of the phase-locked loop control system; In step S6, the steady-state current component I gd ,I gq The function fitting method is: Step S61: Take out the characteristic parameters of each operating point and the PCC point steady-state current component I at each operating point in step S4 gd ,I gq ; Step S62: Taking the characteristic parameter as an independent variable, I gd or I gq For the dependent variable, set the fitting times of each variable, and input the function fitting algorithm to fit the relationship between variables; Step S63: Adjust the fitting times of the respective variables, and take the fitting function with the lowest number of independent variables among the results with a fitting degree greater than the set value to describe the relationship between the steady-state component of the PCC point current and the operating point.

2. A dynamic equivalent modeling method for a new energy grid-connected system according to claim 1, characterized in that: In the kth operation mode in step S1, the admittance measurement method based on the dq coordinate system at the ith measurement frequency is: Step S11: Given the system phase angle in the simulation model, keep the q-axis current disturbance at 0, and apply a frequency of f to the d-axis current. i The sinusoidal disturbance signal is converted into a three-phase current disturbance by coordinate transformation; Step S12: injecting the three-phase current disturbance in step S11 into the PCC point through a controlled current source, and collecting the voltage and current at the PCC point for dq coordinate transformation; Step S13: Separate the frequency f using parameter identification algorithm i The voltage and current are obtained and Step S14: in the simulation model, a system phase angle is given, the d-axis current disturbance is kept at 0, a sinusoidal disturbance signal of a specific frequency is applied to the q-axis current, and the signal is converted into a three-phase current disturbance using an abc coordinate transformation; Step S15: Repeat the process from step S12 to step S13 to obtain and Step S16: Using the voltage and current values ​​in step S13 and step S15, calculate the frequency f i The admittance matrix of the dq coordinate system under 3. A dynamic equivalent modeling method for a new energy grid-connected system according to claim 1, characterized in that: The input signal of the phase-locked loop control system in step S7 is the voltage u of the PCC point in the three-phase stationary coordinate system. pa 、u pb 、u pc .

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