New energy equipment sequence impedance multi-level frequency domain identification method

Abstract

The invention discloses a new energy equipment sequence impedance multi-level frequency domain identification method, and relates to the field of power electronic equipment parameter and model frequency domain identification. Complex vector fitting is carried out on frequency domain response data of impedance measurement, an analytical model or an equivalent zero-pole model of power electronic equipment is obtained, and a basis is provided for grid-connected resonance stability analysis and impedance remodeling; comprising the following steps: S1, carrying out sequence impedance frequency scanning of single harmonic disturbance injection to obtain impedance frequency domain response data; s2, performing complex vector fitting to obtain a pole-residue type port frequency domain model; s3, evaluating'grey / black box 'characteristics according to the transparency of the control architecture information; s4, deducing a theoretical sequence impedance model of the grey box equipment, and identifying parameters based on a pole-residue expression; deducing an equivalent zero pole model for the black box equipment or the new energy cluster; compared with traditional qualitative analysis, accurate quantitative analysis and impedance remodeling are achieved, and analysis accuracy and engineering applicability are improved.

Description

Technical Field

[0001] The present invention relates to the field of parameter and model frequency-domain identification of power electronic equipment, and specifically to a multi-level frequency-domain identification method for sequence impedance of new energy equipment. Background Technique

[0002] With a high proportion of new energy connected to the power grid through power electronic converters, the dynamic characteristics of the power system have changed profoundly. Power electronic equipment has heterogeneity, with complex control structures and numerous parameters. Due to factors such as manufacturer confidentiality, detailed information about the controller is often not available, and power electronic equipment exhibits "black / gray box" dynamic characteristics, making the characteristics of the power system tend to be unknown and causing difficulties in analyzing the grid connection stability and damping control of power electronic equipment.

[0003] Many existing studies have carried out parameter identification of power electronic equipment separately in the time domain and frequency domain. For doubly-fed induction wind turbines, some scholars have applied algorithms such as particle swarm optimization, K-means clustering, and Sindy to identify controller parameters through time-domain operation data. However, such algorithms often require obtaining the operation data of all state variables of the power electronic device to be measured in order to accurately identify the controller parameters. In actual operation, data of the vast majority of state variables in the system are often unavailable. Therefore, such methods are often unable to be applied in engineering practice. Existing frequency-domain identification methods identify controller parameters through the frequency-domain response data of the ports of power electronic equipment. There are mainly algorithms such as recursive least squares method, neural network, and vector fitting. The controller parameters and impedance models are identified by means of iterative optimization, training, fitting, etc. on the discrete frequency response data of the ports of power electronic equipment. However, such methods can only achieve rational function identification and are applicable to the identification of impedance models in the dq coordinate system, and cannot identify non-conjugate pole pairs and complex coefficient cases in the sequence impedance model. At the same time, in actual engineering, the inherent coupling term of dq impedance has no physical meaning and cannot be measured, which makes it difficult for the current frequency-domain identification technology of power electronic equipment to be implemented and practical. Therefore, how to invent and design a method for measuring the frequency-domain response of the ports of power electronic equipment with high engineering practicability and a technology for identifying the parameters of complex sequence impedance models with high accuracy is an urgent problem to be studied in the industrial production field. Summary of the Invention

[0004] Based on the above background, the technical solution proposed by the present invention is: a multi-level frequency-domain identification method for sequence impedance of new energy equipment, which is used to solve the problems mentioned in the above background.

[0005] The object of the present invention can be achieved by the following technical solutions: a multi-level frequency-domain identification method for sequence impedance of new energy equipment, including:

[0006] S1: Conduct a sequence impedance frequency scan with single - harmonic perturbation injection on the power electronic device under test within the frequency range to be analyzed, and obtain discrete data of the impedance frequency - domain response of the device under test at each measurement frequency.

[0007] S2: According to the impedance frequency - response measurement data, perform complex vector fitting to obtain the pole - residue form of the port frequency - domain model of the power electronic device under test.

[0008] S3: Evaluate the gray / black - box characteristics of the power electronic device according to the transparency of the control architecture information of the object under test.

[0009] S4: For the gray - box power electronic device with a known control structure, derive the theoretical analytical sequence impedance model and identify the parameters of the theoretical sequence impedance model based on the pole - residue form; for the black - box power electronic device or the new - energy power - electronic cluster at the substation level, derive the zero - pole form of the equivalent sequence impedance model based on the pole - residue form.

[0010] As a preferred implementation mode of the present invention, in S1, for any power - electronic grid - connected device, apply a small - signal perturbation source with a variable frequency at the grid - connection port, and obtain discrete data points of the device port impedance by calculating the ratio of the perturbation signal to the port response signal at each frequency point, including:

[0011] S11: For the power - electronic device, operate from the initial state to the steady - state operating point under the condition of being connected to an ideal grid, record and maintain the steady - state operation.

[0012] S12: Set positive - sequence and negative - sequence three - phase sinusoidal perturbation signal sources with variable frequencies. The amplitude of the perturbation signal source is 10% of the fundamental - wave amplitude of the power - electronic device under the steady - state grid - connection operation condition; the frequency change range F of the perturbation signal source is [f min , f max , where f min represents the lower frequency limit and f max represents the upper frequency limit; the frequency measurement points are linearly distributed in the low - frequency band [f min , 100] Hz of F with a step size of 1 Hz between adjacent frequency measurement points; in the medium - high - frequency band [100, f max Hz of F, they are logarithmically distributed. All frequency measurement points are combined into a row vector, denoted as the frequency - sweep range f p , and the total number is N.

[0013] S13: When the device is in steady - state operation, inject a positive - sequence three - phase perturbation signal at the grid - connection point. The frequency of the perturbation signal increases sequentially according to the frequency - sweep range f p in step S12. After each change in the frequency of the perturbation signal, wait for the system to run for T s seconds to reach a new steady - state operating point, and measure and record the port voltage and current data of the power - electronic device at this perturbation frequency for 1 second, denoted as Vpb ; For the measurement process of negative-sequence three-phase disturbance signals, it is the same. The port voltage and current data are measured and denoted as V pb ; For the measurement process of negative-sequence three-phase disturbance signals, it is the same. The port voltage and current data are measured and denoted as V nb 、I nb ; Repeat step S13 until the disturbance injection and data measurement are completed for all frequency measurement points;

[0014] S14: Perform a fast Fourier transform on the port voltage and current data of the positive-sequence and negative-sequence disturbance signals at each frequency measurement point within the swept frequency range f p to decompose the port voltage and current components at a specific frequency f p . The positive-sequence ones are denoted as V pp 、I pp , and the negative-sequence ones are denoted as V np 、I np ; Perform positive, negative, and zero-sequence decomposition on V pp 、I pp 、V np 、I np . Retain the positive-sequence components of the positive-sequence disturbance port voltage and current signals and denote them as V pp1 、I pp1 ; Retain the negative-sequence components of the negative-sequence disturbance port voltage and current signals and denote them as V np2 、I np2 ; Then the positive / negative-sequence impedance calculation of the power electronic device port is: Among them, Z ap represents the positive-sequence impedance of the device port, and Z an represents the negative-sequence impedance of the device port.

[0015] As a preferred embodiment of the present invention, in S2, according to the discrete measurement values of the positive-sequence and negative-sequence impedances of the power electronic device, complex vector fitting is performed to obtain the pole-residue form of the port positive / negative-sequence impedance, including:

[0016] S21: Determine the input data form: Convert the swept frequency range f p to the Laplace domain: S p = 2πf p , where S p represents the Laplace variable; Express the discrete measurement values of the positive / negative-sequence impedance as row vectors Z ap 、Z an ; Then the impedance input data set to be subjected to complex vector fitting is (S p ,Z ap ), (S p ,Z an );

[0017] S22: Establish the complex vector fitting pole-residue formula: Based on rational polynomial fitting, represent the frequency response model of the power electronic port through the mathematical expression of the sum of pole-residue formulas: where, f b (s) represents the frequency response model of the power electronic port, s represents the Laplace operator, K represents the model order, p k represents the pole, r k represents the residue, and d is a real number; p k , r k , and d are all parameters to be identified;

[0018] S23: Initial pole setting: The complex vector fitting requires artificial setting of the initial poles. The number of initial poles is equal to the model order K, and the initial poles are expressed as: p k = α k + jβ k ; α k = -c|β k |, where, α k represents the real part of the pole, β k represents the imaginary part of the pole, j is the imaginary unit, and c is the proportionality coefficient; the imaginary part β k of the initial pole is linearly distributed in the frequency range [2πf min , 2πf max ;

[0019] S24: Complex vector least squares fitting: Substitute the input impedance data sets (S p , Z ap ), (S p , Z an ) into f b (s) respectively, and obtain:

[0020]

[0021] where, represents the estimated value of the residue; for any frequency point s p in S n , transform Equation (1) into the least squares form:

[0022] A n x = b n (2)

[0023] where:

[0024]

[0025]

[0026] b n = f(s n )

[0027] According to the sweeping range S p For the total number of medium frequency points, write N equations of formula (2), and transform the identification problem of parameter x into a least-squares fitting problem.

[0028] As a preferred embodiment of the present invention, in S3, according to the transparency of the control architecture information of the power electronic device under test, evaluate the gray / black box characteristics of the power electronic device, including:

[0029] S31: Classify the object under test according to the rated operating condition information of the object under test, distinguish the single-machine operating condition and the substation-level operating condition, and further distinguish the model levels;

[0030] S32: According to the transparency of the control strategy information provided by the power electronic device manufacturer, distinguish the gray / black box characteristics of the single-machine model, and classify the object under test into two categories, the single-machine gray box model and the single-machine and substation-level black box model.

[0031] As a preferred embodiment of the present invention, in S4, according to the pole-residue formula obtained in step S2 and the gray / black box characteristics obtained in step S3, carry out multi-level frequency-domain model equivalent transformation, including:

[0032] S41: For the single-machine "gray box" power electronic device, deduce its theoretical sequence impedance analysis model according to the control architecture and the topology of the device itself; taking the three-phase power electronic converter as the topology framework of the new energy power electronic equipment, the three-phase converter is an inherent unit of wind power, photovoltaic, and flexible DC transmission equipment, representing the nature of the power electronic grid-connected equipment, and deduce the theoretical impedance model of its port:

[0033]

[0034] Among them, Y ap (s), Y an (s) are the positive-sequence admittance and negative-sequence admittance of the power electronic converter port respectively, Y pd (s), Y nd (s) are the AC-DC transfer admittances when positive-sequence and negative-sequence disturbances are applied to the three-phase AC port, Y dp (s), Y dn (s) represent the positive-sequence and negative-sequence transfer admittances of DC-AC when a disturbance is applied to the DC port, Y dd (s) represents the self-admittance when a disturbance is applied to the DC port, Y pp (s), Y nn (s) represent the positive-sequence and negative-sequence self-admittances when positive-sequence and negative-sequence disturbances are applied to the three-phase AC port; Z dc (s) represents the small-signal impedance of the DC side system of the three-phase converter, and the calculation method is different for different new energy grid-connected scenarios; s +1, s -1 respectively represent shifting the frequency up and down by one fundamental wave; based on the known control architecture, substitute the transfer function of the controller containing unknown control parameters into the positive / negative sequence admittance, and derive the positive / negative sequence admittance into the theoretical pole-residue form:

[0035]

[0036] where r kp , r kn respectively represent the residues of the positive and negative sequence admittances, p kp , p kn respectively represent the poles of the positive and negative sequence admittances, d p , d n respectively represent the remaining constant terms of the positive and negative sequence admittances; based on the pole-residue form of the power electronic device port obtained by fitting the swept-frequency data in step S2, identify the control parameters for the theoretical pole-residue form, and then realize the frequency-domain identification of the sequence impedance of the gray-box power electronic device. The obtained Y ap (s), Y an (s) are the theoretical admittance expressions of the power electronic device, which are directly used for the system stability analysis based on the impedance method;

[0037] S42: For single-machine and substation-level black-box power electronic devices, derive the zero-pole formula of the device according to the pole-residue form of the device port obtained in step S2:

[0038]

[0039] where Y(s) represents the zero-pole formula of the port admittance of the single-machine and substation-level power electronic device, β represents the numerator coefficient, α represents the denominator coefficient, m and n respectively represent the orders of the numerator and denominator, and s represents the Laplace operator; by solving the zeros of Y(s) and judging whether the zeros fall in the right half-plane, the grid connection stability of the single-machine or substation-level power electronic device can be analyzed.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] 1. The present invention can accurately measure the frequency-domain discrete data of the power electronic sequence impedance model through single-harmonic injection, and then can realize the complex vector fitting of the frequency-domain discrete data, accurately restoring the theoretical sequence impedance model or equivalent impedance zero-pole formula with complex coefficients and non-conjugate pole pairs, laying a foundation for the grid connection stability analysis and damping controller design of "gray / black-box" power electronic devices.

[0042] 2. The present invention has practical applicability in the whole process of engineering. The impedance measurement has the advantages of being easy to implement and being compatible with various power electronic devices, solving the problem that the coupling impedance cannot be measured in traditional impedance measurement. Compared with traditional identification algorithms, the complex vector fitting algorithm has the advantages of strong adaptability and high accuracy, and can be applied to the identification of non-ideal impedance measurement data.

[0043] 3. Compared with traditional identification methods, the multi-level impedance frequency-domain identification method of the present invention has the advantages of a wide range of applicable scenarios and high efficiency. This method divides the transparency and levels of power electronic devices according to known information, and adaptively selects different impedance model structures to identify the system impedance model for "grey box" single-machine systems, "black box" single-machine and substation-level systems, realizing accurate analysis of the grid connection stability of "black / grey" box systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] For the convenience of those skilled in the art to understand, the present invention will be further described below with reference to the accompanying drawings.

[0045] Figure 1 is the flowchart of the method of the present invention;

[0046] Figure 2 is the schematic diagram of the sequence impedance frequency scan of the present invention;

[0047] Figure 3 is the schematic diagram of the topology of the three-phase converter driven by a constant power source of the present invention;

[0048] Figure 4 is the schematic diagram of the sequence impedance frequency-domain identification result of the three-phase converter based on complex vector fitting of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0050] It should be understood that the terms "including" and "comprising" used in the specification and claims of this disclosure indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0051] It should also be understood that the terms used in this disclosure specification are only for the purpose of describing specific embodiments and are not intended to limit this disclosure. As used in this disclosure specification and the claims, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms. It should further be understood that the term " / 1or" used in this disclosure specification and the claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0052] Please refer to Figures 1-4 As shown, a method for multi-level frequency-domain identification of the sequence impedance of a new energy equipment includes:

[0053] To describe the present invention more specifically, the present invention will be further described below in conjunction with the specification drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0054] As Figure 1 As shown, the steps of this embodiment for a three-phase power electronic converter driven by a constant power source include:

[0055] S1: Conduct a sequence impedance frequency scan with single-harmonic perturbation injection on the three-phase grid-connected inverter to be measured within the frequency range to be analyzed, and obtain the discrete data of the impedance frequency-domain response of the device to be measured at each measurement frequency;

[0056] S2: According to the impedance frequency response measurement data, perform complex vector fitting to obtain the pole-residue form of the port frequency-domain model of the power electronic device to be measured;

[0057] S3: Evaluate the "gray / black" box characteristics of the power electronic device according to the transparency of the control architecture information of the object to be measured;

[0058] S4: For the gray-box power electronic device with a known control structure, deduce the theoretical analytical sequence impedance model and identify the parameters of the theoretical sequence impedance model based on the pole-residue form. For the black-box power electronic device or the new energy power electronic cluster at the station level, deduce the zero-pole form of the equivalent sequence impedance model based on the pole-residue form.

[0059] In the step S1, first, the three-phase power electronic converter driven by a constant power source is operated from the initial state to the rated steady-state operating condition. A three-phase voltage disturbance is injected at the ports of the three-phase power electronic converter. The frequency of the voltage disturbance is distributed between 1 Hz and 10 kHz. When injecting a disturbance of a certain frequency, after the system operates for 5 seconds, 1-second operating data of the three-phase voltage and current at the grid-connected port are collected. The steps of frequency injection and data collection are repeated until the data measurement is completed for all frequency disturbance points. The measured discrete frequency-domain response data is subjected to FFT analysis, and positive, negative, and zero-sequence decompositions are performed to obtain the ratio of the voltage disturbance to the current response at each frequency, and the sequence impedance measurement value of the power electronic device is obtained. Specifically, it includes:

[0060] S11. Establishment of steady-state operating point. For the power electronic device, it is operated from the initial state to the steady-state operating point under the condition of being connected to an ideal grid, and the steady-state operation is recorded and maintained.

[0061] S12. Setting of disturbance signal source. Set positive-sequence and negative-sequence three-phase sinusoidal disturbance signal sources with variable frequencies. The amplitude of the disturbance signal source is 10% of the fundamental wave amplitude under the steady-state grid-connected operating condition of the power electronic device. The frequency change range F of the disturbance signal source is [f min , f max , where f min represents the lower frequency limit, and f max represents the upper frequency limit. The frequency measurement points are linearly distributed in the low-frequency band [f min , 100] Hz of F, and the step size between adjacent frequency measurement points is 1 Hz; in the medium-high frequency band [100, f max Hz of F, they are logarithmically distributed. All frequency measurement points are combined into a row vector, denoted as the frequency sweep range f p , and the total number is N.

[0062] S13. Disturbance injection and data measurement. When the device is operating in a steady state, a positive-sequence three-phase disturbance signal is injected at the grid-connected point. The frequency of the disturbance signal increases sequentially according to the frequency sweep range f p in step S12, such as Figure 2 . After each change in the frequency of the disturbance signal, after the system operates for T s seconds to reach a new steady-state operating point, the voltage and current data at the ports of the power electronic device at this disturbance frequency for 1 second are measured and recorded, denoted as V pb , I pb . The measurement process for the negative-sequence three-phase disturbance signal is the same, and the measured port voltage and current data are denoted as V nb , I nb . Step S13 is repeated until the disturbance injection and data measurement are completed for all frequency measurement points.

[0063] S14. Data processing and impedance calculation. For the positive-sequence and negative-sequence disturbance signals in the frequency sweep range fp Perform a fast Fourier transform (FFT) on the port voltage and current data at each frequency measurement point within, and decompose the port voltage and current components at a specific frequency f p The positive sequence is denoted as V pp 、I pp The negative sequence is denoted as V np 、I np . For V pp 、I pp 、V np 、I np Perform positive, negative, and zero-sequence decomposition. For the positive-sequence perturbed port voltage and current signals, retain the positive-sequence components, denoted as V pp1 、I pp1 ; for the negative-sequence perturbed port voltage and current signals, retain the negative-sequence components, denoted as V np2 、I np2 , and eliminate the influence brought by three-phase imbalance. Then the positive / negative-sequence impedance calculation of the power electronic device port is:

[0064]

[0065] where Z ap represents the positive-sequence impedance of the device port, and Z an represents the negative-sequence impedance of the device port.

[0066] In the step S2, perform complex vector fitting on the sequence impedance measurement values through a fixed pole-residue formula , determine the fitting order as 5th order, and obtain the analytical pole-residue expression of the sequence impedance measurement values. Specifically, it includes:

[0067] S21. Determine the form of the input data. Convert the swept frequency range f p to the Laplace domain:

[0068] S p =2πf p

[0069] where S p represents the Laplace variable. Express the positive / negative-sequence impedance discrete measurement values as row vectors Z ap 、Z an . Then the impedance input data set to be subjected to complex vector fitting is (S p ,Z ap ), (S p ,Z an ).

[0070] S22. Establish a complex vector fitting pole-residue formula. Based on rational polynomial fitting, characterize the frequency response model of the power electronic port through a mathematical expression of the sum of pole-residue formulas.

[0071]

[0072] Among them, f b (s) represents the frequency response model of the power electronic port, s represents the Laplace operator, K represents the model order, p k represents the pole, r k represents the residue, and d is a real number. p k , r k , and d are all parameters to be identified.

[0073] S23. Initial pole setting. Complex vector fitting requires manual setting of the initial poles. The number of initial poles is equal to the model order K, and the initial poles are expressed as:

[0074] p k = α k + jβ k ; α k = -c|β k |

[0075] Among them, α k represents the real part of the pole, β k represents the imaginary part of the pole, j is the imaginary unit, and c is the proportionality coefficient. The imaginary part β k of the initial pole is linearly distributed in the frequency range [2πf min , 2πf max . The default value of the proportionality coefficient c is 0.001.

[0076] S24. Complex vector least squares fitting. Substitute the input impedance data sets (S p , Z ap ), (S p , Z an ) into f b (s) respectively, and obtain:

[0077]

[0078] Among them, represents the estimated value of the residue. For any frequency point s p in S n , equation (1) can be transformed into the least squares form:

[0079] A n x = b n (2)

[0080] Among them,

[0081]

[0082] b n = f(s n )

[0083] According to the leveling range S p For the total number of medium frequency points, a total of N equations (2) can be written. At this time, the identification problem of parameter x is transformed into a least squares fitting problem.

[0084] In step S3, according to the three-phase converter control architecture and strategy information provided by the manufacturer, it is determined that the three-phase power electronic converter with constant power drive in this embodiment is of the "grey box" nature. Specifically, it includes:

[0085] S31. According to the rated operating condition information of the object under test, classify the object under test, distinguish the single-machine operating condition and the substation-level operating condition, and further distinguish the model levels.

[0086] S32. Further, according to the transparency of the control strategy information provided by the power electronic equipment manufacturer, distinguish the "grey / black box" characteristics of the single-machine model. Finally, the object under test is divided into two categories: the single-machine "grey box" model and the single-machine and substation-level "black box" model.

[0087] In step S4, based on the "grey box" characteristics of the equipment, deduce the theoretical analytical expression of the sequence impedance of the equipment ports And further deduce the theoretical analytical expression of Y ap (s) according to the pole-residue form in step S2 to obtain the pole-residue expression of the theoretical sequence impedance Finally, complete the identification of the sequence impedance parameters of the three-phase converter. If the evaluation result in step S3 is a "black box" system, then in step S4, deduce the zero-pole form of the equipment based on the pole-residue formula. Specifically, it includes:

[0088] S41. For the single-machine "grey box" power electronic equipment, according to the control architecture and the topology of the equipment itself, its theoretical sequence impedance analytical model can be deduced. Taking the three-phase power electronic converter as an example, such as Figure 3 , as the most typical topological framework of new energy power electronic equipment, the three-phase converter is an inherent unit of wind power, photovoltaic, and flexible DC transmission equipment, and can represent the general properties of power electronic grid-connected equipment. Deduce the theoretical impedance model with general significance at its ports:

[0089]

[0090] Among them, Y ap (s), Y an (s) are the positive sequence admittance and negative sequence admittance of the power electronic converter ports respectively, Y pd (s), Y nd (s) are the AC-DC transfer admittances when positive sequence and negative sequence perturbations are applied to the three-phase AC ports, Y dp (s), Y dn(s) represents the positive-sequence and negative-sequence transfer admittances from DC to AC when a perturbation is applied to the DC port, Y dd (s) represents the self-admittance when a perturbation is applied to the DC port, Y pp (s), Y nn (s) represents the positive-sequence and negative-sequence self-admittances when positive-sequence and negative-sequence perturbations are applied to the three-phase AC port. Z dc (s) represents the small-signal impedance of the DC side system of the three-phase converter. The calculation method is different for different new energy grid-connected scenarios. s +1 , s -1 respectively represent shifting the frequency up by one fundamental wave and down by one fundamental wave. Based on the known control architecture, substitute the transfer function of the controller containing unknown control parameters into the positive / negative-sequence admittance, and derive the positive / negative-sequence admittance into the theoretical pole-residue form:

[0091]

[0092] where, r kp , r kn respectively represent the residues of the positive-sequence and negative-sequence admittances, p kp , p kn respectively represent the poles of the positive-sequence and negative-sequence admittances, d p , d n respectively represent the remaining constant terms of the positive-sequence and negative-sequence admittances. Based on the pole-residue form of the power electronic device port obtained by fitting the sweep frequency data in step S2, identify the control parameters for the theoretical pole-residue form, and then realize the frequency-domain identification of the sequence impedance of the "grey-box" power electronic device. The obtained Y ap (s), Y an (s) is the theoretical admittance expression of the power electronic device, which can be directly used for the system stability analysis based on the impedance method.

[0093] S42. For single-machine and substation-level "black-box" power electronic devices, according to the pole-residue form of the device port obtained in step S2, derive the zero-pole form of the device:

[0094]

[0095] where, Y(s) represents the zero-pole form of the port admittance of the single-machine and substation-level power electronic device, β represents the numerator coefficient, α represents the denominator coefficient, m and n respectively represent the orders of the numerator and denominator, and s represents the Laplace operator. By solving the zeros of Y(s) and judging whether the zeros fall in the right half-plane, the grid connection stability of the single-machine or substation-level power electronic device can be analyzed.

[0096] To verify the effectiveness of the present invention, the example method of the present invention is now applied to the grid connection scenario of a three-phase power electronic converter driven by a constant power source. The architecture of the three-phase power electronic converter is as Figure 3 shown. Figure 4The port sequence impedance measurement results (red dotted line), complex vector fitting identification results (blue dashed line), and theoretical analytical sequence impedance results (orange solid line) of a three-phase power electronic converter driven by a constant power source are shown. The coincidence degree between the sequence impedance model identified by complex vector fitting and the impedance measurement results is extremely high, and there is a very small model error (green solid line) between the identification results and the theoretical sequence impedance curve, indicating the accuracy of equipment parameter identification and verifying the effectiveness of the sequence impedance identification method based on complex vector fitting of the present invention.

[0097] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only the specific embodiments. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A multi-level frequency domain identification method for the sequence impedance of new energy equipment, characterized in that, Including: S1: Conduct a sequence impedance frequency scan of the power electronic device under test with single - harmonic perturbation injection within the frequency range to be analyzed, and obtain discrete data of the impedance frequency - domain response of the device under test at each measurement frequency; S2: Based on the impedance frequency - response measurement data, perform complex vector fitting to obtain the pole - residue form of the port frequency - domain model of the power electronic device under test; S3: Evaluate the grey / black - box characteristics of the power electronic device according to the transparency of the control architecture information of the object under test; S4: For the grey - box power electronic device with a known control structure, deduce the theoretical analytical sequence impedance model and identify the parameters of the theoretical sequence impedance model based on the pole - residue form; for the black - box power electronic device or the new - energy power - electronic cluster at the substation level, deduce the zero - pole form of the equivalent sequence impedance model based on the pole - residue form.

2. The multi-level frequency domain identification method for the sequence impedance of a new energy equipment according to claim 1, characterized in that, In S1, for any power - electronic grid - connected device, apply a small - signal perturbation source with a changing frequency at the grid - connection port, and obtain discrete data points of the device port impedance by calculating the ratio of the perturbation signal to the port response signal at each frequency point; Including: S11: For the power - electronic device, operate from the initial state to the steady - state operating point under the condition of being connected to an ideal grid, record and maintain the steady - state operation; S12: Set a positive-sequence and negative-sequence three-phase sinusoidal disturbance signal source with variable frequency. The amplitude of the disturbance signal source is 10% of the fundamental wave amplitude under the grid-connected steady-state operation condition of the power electronic device; the frequency change range F of the disturbance signal source is [f min , f max , where f min represents the lower frequency limit and f max represents the upper frequency limit; the frequency measurement points are linearly distributed in the low-frequency band [f min , 100] Hz with a step size of 1 Hz between adjacent frequency measurement points; in the medium-high frequency band [100, f max Hz, they are logarithmically distributed. All frequency measurement points are combined into a row vector, denoted as the frequency sweep range f p , and the total number is N; S13: When the device is in a steady parallel operation state, a positive-sequence three-phase disturbance signal is injected at the point of common coupling, and the frequency of the disturbance signal increases sequentially according to the frequency sweep range f in step S12. p After each change in the frequency of the disturbance signal, wait for the system to run for T s seconds to reach a new steady-state operating point, measure and record the port voltage and current data of the power electronic device at this disturbance frequency for 1 second, denoted as V pb , I pb ; The measurement process for the negative-sequence three-phase disturbance signal is the same. The measured port voltage and current data are denoted as V nb , I nb ; Repeat step S13 until the disturbance injection and data measurement have been completed for all frequency measurement points. S14: Perform fast Fourier transform on the port voltage and current data at each frequency measurement point within the sweep frequency range f p to decompose the port voltage and current components at a specific frequency f p . Denote the positive-sequence as V pp and I pp , and the negative-sequence as V np and I np . Perform positive, negative, and zero-sequence decomposition on V pp , I pp , V np , and I np . Retain the positive-sequence components of the positive-sequence perturbed port voltage and current signals, denoted as V pp1 and I pp1 . Retain the negative-sequence components of the negative-sequence perturbed port voltage and current signals, denoted as V np2 and I np2 . Then the positive / negative-sequence impedance calculation of the power electronic device port is: where Z ap represents the positive-sequence impedance of the device port, and Z an represents the negative-sequence impedance of the device port.

3. A method for multi-level frequency-domain identification of the sequence impedance of a new energy equipment according to claim 1, characterized in that, In S2, based on the discrete measured values of the positive - sequence and negative - sequence impedances of the power - electronic device, perform complex vector fitting to obtain the pole - residue form of the positive / negative - sequence impedance of the port, including: S21: Determine the form of the input data: Convert the frequency sweep range f p to the Laplace domain: S p = 2πf p , where S p represents the Laplace variable; Express the positive / negative sequence impedance discrete measurement values as row vectors Z ap , Z an ; Then the impedance input data set to be subjected to complex vector fitting is (S p , Z ap ), (S p , Z an ); S22: Establish a complex vector fitting pole-residue formula: Based on rational polynomial fitting, represent the frequency response model of the power electronic port through the mathematical expression of the sum of pole-residue formulas: where f b (s) represents the frequency response model of the power electronic port, s represents the Laplace operator, K represents the model order, p k represents the pole, r k represents the residue, and d is a real number; p k , r k , and d are all parameters to be identified; S23: Initial Pole Setting: Complex vector fitting requires manual setting of initial poles. The number of initial poles is equal to the model order K, and the initial poles are expressed as: p k = α k + jβ k ; α k = -c|β k |, where α k represents the real part of the pole, β k represents the imaginary part of the pole, j is the imaginary unit, and c is the proportionality coefficient; the imaginary part β k of the initial poles is linearly distributed over the frequency range [2πf min , 2πf max ; S24: Complex vector least squares fitting: Substitute the input impedance data sets (S p , Z ap ), (S p , Z an ) into f b (s) respectively, and obtain: Among them, represents the estimated value of the residue; for any frequency point s p in S n , transform Equation (1) into the least squares form: A n x = b n (2) Where: b n = f(s n ) According to the sweeping range S p Based on the total number of medium frequency points, N equations of formula (2) are written, and the identification problem of parameter x is transformed into a least-squares fitting problem.

4. A method for multi-level frequency-domain identification of sequence impedance of a new energy equipment according to claim 1, characterized in that In S3, evaluate the grey / black - box characteristics of the power - electronic device according to the transparency of the control - architecture information of the power - electronic device under test, including: S31: Classify the object under test according to the rated - condition operation information of the object under test, distinguish between the single - machine operation condition and the substation - level operation condition, and further distinguish the model levels; S32: According to the transparency of the control - strategy information provided by the power - electronic device manufacturer, distinguish the grey / black - box characteristics of the single - machine model, and classify the object under test into two categories: the single - machine grey - box model and the single - machine and substation - level black - box model.

5. A method for multi-level frequency-domain identification of the sequence impedance of a new energy equipment according to claim 1, characterized in that In S4, based on the pole - residue form obtained in step S2 and the grey / black - box characteristics obtained in step S3, carry out multi - level frequency - domain model equivalent transformation, including: S41: For the single - machine "grey - box" power - electronic device, deduce its theoretical sequence impedance analytical model according to the control architecture and the topology of the device itself; take the three - phase power - electronic converter as the topology framework of the new - energy power - electronic equipment. The three - phase converter is an inherent unit of wind power, photovoltaic, and flexible DC transmission equipment, which characterizes the nature of the power - electronic grid - connected device, and deduce the theoretical impedance model of its port: Among them, Y ap (s), Y an (s) are the positive-sequence admittance and negative-sequence admittance of the power electronic converter port respectively, Y pd (s), Y nd (s) are the AC-DC transfer admittances when positive-sequence and negative-sequence perturbations are applied to the three-phase AC port, Y dp (s), Y dn (s) represent the positive-sequence and negative-sequence transfer admittances from DC to AC when a perturbation is applied to the DC port, Y dd (s) represents the self-admittance when a perturbation is applied to the DC port, Y pp (s), Y nn (s) represent the positive-sequence and negative-sequence self-admittances when positive-sequence and negative-sequence perturbations are applied to the three-phase AC port; Z dc (s) represents the small-signal impedance of the three-phase converter DC-side system, and the calculation method is different for different new energy grid connection scenarios; s +1 , s -1 respectively represent shifting the frequency up and down by one fundamental wave; based on the known control architecture, substitute the controller transfer function containing unknown control parameters into the positive / negative-sequence admittance, and derive the positive / negative-sequence admittance into the theoretical pole-residue form: where r kp and r kn represent the positive and negative sequence admittance residues respectively, p kp and p kn represent the positive and negative sequence admittance poles respectively, d p and d n represent the positive and negative sequence admittance remaining constant terms respectively; Based on the pole-residue formula of the power electronic device port obtained by fitting the swept frequency data in step S2, the control parameters of the theoretical pole-residue formula are identified, and then the sequence impedance frequency domain identification of the grey-box power electronic device is realized. The obtained Y ap (s) and Y an (s) are the theoretical admittance expressions of the power electronic device and are directly used for the system stability analysis based on the impedance method; S42: For the single - machine and substation - level black - box power - electronic device, deduce the zero - pole form of the device according to the pole - residue form of the device port obtained in step S2: Where, Y(s) represents the zero - pole form of the port admittance of the single - machine and substation - level power - electronic device, β represents the numerator coefficient, α represents the denominator coefficient, m and n represent the orders of the numerator and denominator respectively, and s represents the Laplace operator; by solving the zeros of Y(s) and judging whether the zeros fall into the right - half plane, the grid - connection stability of the single - machine or substation - level power - electronic device can be analyzed.

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