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25 August 2023, Volume 43 Issue 4

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Researches and Tests

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Study on Natural Convective Flow Heat Transfer in Supercritical Carbon Dioxide Cavity

YE Maojing, WU Tianyu, LIU Kairui, WANG Limin, CHE Defu

2023, 43(4):  1-8.  doi:10.3969/j.issn.1008-0198.2023.04.001

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Horizontal flow of supercritical carbon dioxide (S-CO₂) will flow stratification under heating or cooling conditions, resulting in different heat transfer phenomena at the top and bottom of the tube. In order to study the flow heat transfer behavior driven by upward lift in vertical flow direction, the development process of S-CO₂ natural convection and the influence of pressure, pipe diameter and temperature interval on the development process are studied based on a two-dimensional circular cavity physical model. The results show that the development process of flow heat transfer away from the pseudo-critical temperature range is relatively stable compared with the pseudo-critical temperature range. In the pseudo-critical temperature range, the higher the pressure, the faster the heat transfer development process. In the pseudo-critical temperature range, the larger the diameter of the pipe, the longer the time for heat transfer to reach stability, and the more intense the main flow zone is in the initial stage of development.

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A New Approach Law Sliding Mode Fault Tolerant Control Method for Double Fed Induction Generator Actuator Fault

LI Shengqing, WEN Yanxi, CHEN Xin

2023, 43(4):  9-15.  doi:10.3969/j.issn.1008-0198.2023.04.002

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In order to overcome the gain-bias fault of the actuator during the operation of the double fed induction generator, a second order non-singular fast terminal sliding mode fault tolerant control is designed by combining the PID sliding surface with the nonlinear non-singular terminal sliding mode surface, and by associating the sliding mode surface function with the control gain using a new adaptive reaching law. Then Lyapunov function is used to prove the stability of the controller. The simulation and experimental results show that compared with the traditional PID and the traditional sliding mode control, the proposed control method weakens chattering, improves the response speed by 49.8%, reduces the steady-state error of the system, and has better fault tolerance.

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Ahead Optimal Dispatch of Multi Energy Power System Considering Power Flexibility and Complementarity

XIAO Bai, ZHANG Bo

2023, 43(4):  16-23.  doi:10.3969/j.issn.1008-0198.2023.04.003

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A multi energy power system day ahead optimization scheduling method considering power flexibility and complementarity is proposed to address the volatility and intermittency of wind and photovoltaic power generation, as well as the coordinated and optimized operation of multi energy power systems. Firstly, a supply and demand model for power flexibility and complementarity is established. Then, a multi-objective coordinated hierarchical optimization scheduling model for wind power, solar power, hydroenergy, gas energy, and thermal power,energy storage storage is constructed with the optimization objectives of optimizing the economy and stability of thermal power operation, and minimizing the total pollutant emissions. Renewable energy complementary power sources and complementary power demand indicators are defined, and the aggregation ratio of renewable energy complementary power sources is determined to minimize the complementary power demand indicators. Finally, the artificial bee colony algorithm is improved by introducing dynamic probability and developing the optimal guidance strategy for the bee colony, and the improved artificial bee colony algorithm is used to solve the established optimization scheduling model. The numerical results show that the proposed model and algorithm are feasible for the multi energy complementary coordinated scheduling problem.

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Load Aggregator Strategic Quotation and Peak Market Clearing Optimization Considering Adjustment Cost

ZHANG Lingqiao, ZHOU Zhengcheng, SHEN Shasha, XIANG Yunkun, LIU Hanlin, WANG Wei, MENG Ke

2023, 43(4):  24-31.  doi:10.3969/j.issn.1008-0198.2023.04.004

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The access of high proportion of new energy makes the uncertainty of power supply increasing, the unbalance of power supply outstanding and the difference between peak and valley of load increasing. In order to solve the problem of unbalance of power supply and demand during peak hours, a strategic bidding strategy of load aggregator considering adjusting cost and its optimal clearing strategy in peak market are proposed. Firstly, the load aggregator is defined, and the flexible resource is classified according to the characteristics of voltage level, load curve, unit power regulation cost and power consumption characteristics. Secondly,the paper analyzes the characteristics and adjustment potential of various kinds of end-user load, establishes the model of load adjustment cost of various kinds of end-users, and constructs the strategic quotation model, to minimize the sum of load adjustment costs of load aggregators, a clearing model is established. Finally, a typical peak demand response scenario involving a regional load aggregator is taken as an example to demonstrate the validity and scientificity of the proposed method.

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Mechanism and Hierarchical Coordinated Control of Solar Photovoltaic Inverter Cluster Resonance in Civil Buildings

DING Jinsong, YAO Hongde, LI Shengqing, MENG Huanping, ZHU Hui

2023, 43(4):  32-39.  doi:10.3969/j.issn.1008-0198.2023.04.005

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The clustering of photovoltaic(PV) inverter in residential buildings is prone to harmonic resonance, which seriously affects system stability and power quality. To address this problem, a mathematical model of PV inverter clusters connected to the grid is established, the resonance mechanism and resonance characteristics of single inverters and inverter clusters are derived, and a hierarchical coordination control strategy for PV inverter cluster resonance is proposed. In the first layer, for the inherent resonance of LCL-type PV inverters, an active damping method based on capacitor-voltage inertia feedback with forward-channel series trap is proposed.In the second layer, for the resonance generated by the coupling of PV inverter clusters with grid impedance,a method for suppressing the resonance of parallel virtual admittance of common coupling points is proposed.The grid-connected current quality is improved through the hierarchical division and coordinated control of the grid-connected resonance of inverter clusters.The simulation results show that compared with the traditional capacitor current feedback strategy, the harmonic distortion rate of grid-connected current decreases obviously, and the grid-connected resonant of the inverter is effectively suppressed, which proves the feasibility of the proposed strategy.

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Research on Multi-Objective Optimal Control of Virual Synchronous Generator Inverter in Unbalanced Power Grid Based on Wolf Pack Algorithm

ZHU Hongping, ZHU Hongzhi, QIAN Wanming, GUO Liwen, HAN Yinglong

2023, 43(4):  40-47.  doi:10.3969/j.issn.1008-0198.2023.04.006

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This paper presents a multi-objective coordinated optimal control of virtual synchronous generator(VSG)inverter based on wolf swarn algorithm to address the issues of unbalanced grid connected output current and fluctuations in active and reactive power when the grid voltage is unbalanced.For the current balance, suppression of active and reactive power fluctuations between the contradictions,a multi-objective optimization control is designed, introducing adjustment coefficients and imbalance, and establishing a unified expression for negative sequence reference current and a multi-objective optimization function. And through the wolf swarm algorithm, the multi-objective function is optimized to achieve coordinated control among the three controls, improving the output power quality of the VSG inverter. Finally, the proposed control method is simulated to verify its feasibility and effectiveness.

New technology and Application

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Capacity Optimization Configuration of Grid-Connected Wind-Solar-Hydrogen-Storage Microgrid

ZHAO Na, ZHANG Lian, WANG Shibin, LI Duo, HUANG Wei

2023, 43(4):  48-55.  doi:10.3969/j.issn.1008-0198.2023.04.007

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A single type of energy storage device is difficult to take into account the advantages of multiple types of energy storage devices, while the hybrid energy storage system can integrate the technical and economic advantages of different types of energy storage. Aiming at the optimal configuration of hybrid energy storage based on battery and hydrogen energy storage in grid-connected mode, economic and environmental protection are taken as the objective function, the analytic hierarchy process is used to solve the multi-objective weight problem, and the particle swarm optimization algorithm is used to solve the optimal configuration of microgrid capacity. Different energy storage configuration schemes are analyzed and compared by economy and evaluation index. The results show that the cost of hybrid energy storage is 2.46% and 10.02% lower than that of single battery and hydrogen energy storage. The self-balancing rate is 7.65% and 23.89% higher than that of single battery and hydrogen energy storage, and the redundancy is 19% and 38.16% lower than that of single battery and hydrogen energy storage.

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Governance Method of Power Quality in New Power Distribution Area Based on Energy Storage System

LAN Zheng, YIN Rui, ZOU Bin, HE Dong

2023, 43(4):  56-62.  doi:10.3969/j.issn.1008-0198.2023.04.008

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In the new power distribution area, due to the wide application of power electronic devices and the access of a large number of distributed energy sources, the power quality of the new power distribution area is seriously affected and the power fluctuation is caused. In order to improve the power quality and power fluctuation of the new power distribution area, a new power quality management method based on energy storage system is proposed. This method can improve the comprehensive adjusting ability of the energy storage system at the head of the area. It can not only control the current harmonics, reactive power and unbalance current of the new power distribution area, but also stabilize the active power effectively. Firstly, the structure of the new power distribution area and the topology of the energy storage system are introduced, and the mathematical model is built. Then, in the harmonic detection section of the control section, the four-wire i_p-i_q harmonic detection method based on moving mean filter is adopted. And in the process of energy storage power adjustment, the strategy of battery charging and discharging considering energy storage capacity is adopted. At the same time, the command current is accurately tracked by repetitive control and PI control. Finally, the simulation results show that the proposed energy storage system and its control strategy can not only effectively improve the power quality of the new power distribution area, but also smooth the active power fluctuation.

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Strategy of An Improved Adaptive Sliding Mode Controlling Virtual Synchronous Generator Control Based on Direct-Driven Permanent Magnet Wind Power System

CHEN Anping, HU Xiaolin, LUO Zhaoxu, CHENG Zhun

2023, 43(4):  63-73.  doi:10.3969/j.issn.1008-0198.2023.04.009

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For the direct-drive permanent magnet synchronous wind generator system, because of the difference of equivalent output impedance between inverters and transmission line impedance, the problems of multi-inverters controlled by traditional virtual synchronous generator (VSG) , such as unequal power distribution and poor circulating current suppression are presented,and an improved adaptive sliding mode control strategy is proposed for multiple VSG power sharing and circulation suppression. The given power calculating is calculated according to the total load capacity and the capacity of each inverter, and the virtual impedance according to the given reactive power to compensate the voltage drop caused by the difference of line impedance is adjusted .The sliding mode control of two VSG is designed in coordinate system, and the sliding mode surface is designed based on the difference between the inverter output voltage and the VSG reference voltage, based on Lyapunov stability theory, an adaptive sliding mode controller is designed, which consists of equivalent control, switching control and adaptive compensation. Compared with the traditional control method, the proposed control strategy power sharing and circulation suppression are achieved , and the distribution accuracy of reactive power and VSG output voltage are improved. Finally, the correctness and validity of the control strategy are verified in MATLAB/Simulink.

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Research on Distortion Correction Method of Aerial Photovoltaic Module Images

WANG Jiawen, ZHU Yongcan, WANG Shuai, LI Kefeng

2023, 43(4):  74-79.  doi:10.3969/j.issn.1008-0198.2023.04.010

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Aerial photography of photovoltaic components often suffers from distortion due to shooting angle issues, which affects the measurement, recognition, and classification of elements like straight lines, angles, and proportions. To address this problem, this paper proposes an undistorted aerial photovoltaic component image correction method that requires no calibration. The approach first extracts four critical feature points from the photovoltaic component image using a feature point extraction algorithm and then matches them using a feature point matching algorithm to obtain their corresponding relationships before and after distortion. Secondly, the theoretical principles of computational geometry are utilized to compute the parameters T necessary for distortion correction through triangulation and coordinate transformation of the corresponding points. Finally, distortion correction is carried out on the image using parameter T to obtain the corrected photovoltaic component image. This algorithm not only improves the visual correction effect of the image but also increases the accuracy of data by 20%~55%.This method has a high application value in the foreign object recognition, operation and maintenance of the aerial photovoltaics module image.

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Measurement and Simulation Analysis of Electrochemical Energy Storage Power Station Model

HONG Quan, YANG Dan, XIONG Shangfeng, SUN Jieyi, LI Li, DING Yu

2023, 43(4):  80-84.  doi:10.3969/j.issn.1008-0198.2023.04.011

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In order to broaden the application range of electrochemical energy storage in power grid regulation, and make full use of its advantages of flexible active and reactive power regulation and fast response speed, it is necessary to establish a model for power grid simulation analysis, which provides an analysis basis for electrochemical energy storage to participate in multiple scenarios such as peak shaving, frequency modulation, voltage regulation and transient reactive power support. In this paper, the measurement method of electromechanical simulation model of electrochemical energy storage power station is studied. Based on the parameter identification method of response characteristic matching and the field measurement characteristics, the simulation analysis model of an energy storage station in Hunan province is established, and its effect on improving the transient voltage characteristics of Hunan power grid is analyzed, which has certain engineering application value.

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Heat Dissipation Optimization Design for Outdoor Box Capacitors

ZHANG Yuan, WANG Shuo

2023, 43(4):  85-89.  doi:10.3969/j.issn.1008-0198.2023.04.012

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Outdoor box capacitors often encounter problems such as uneven temperature, water leakage at the inlet and outlet, and dust blockage in traditional left and right ventilation and heat dissipation methods in rainy, snowy, cold, or high-temperature environments. A heat dissipation scheme for side inlet and top outlet air is design based on the internal configuration and heat dissipation requirements of box capacitors. By optimizing the number and position of air inlet and outlet, fans and installing guide plates at the air inlet, the internal components meet the heat dissipation requirements at an ambient temperature of 55 ℃, and the box body meets the structural protection requirements of IP54. The actual operation effect of this scheme is good, providing a reference for the heat dissipation design of box capacitors.

Experience and Discussion

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Finite Element Simulation of Abrasive Wear Characteristics for a Ring Chain Line Fitting

ZENG Ping, LIU Zhigang, HUANG Changyong, LUO Fangxu, ZHANG Huapeng, CAI Xinjing

2023, 43(4):  90-94.  doi:10.3969/j.issn.1008-0198.2023.04.013

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Electric power fittings located in the strong wind area are prone to abrasive wear. In order to study abrasive wear mechanism of electric power fittings, the wear process of a ring chain line fitting is simulated based on the finite element method. It is indicated that the maximum stress of the U-shaped ring is 692.2 MPa, far exceeding the yield strength of 45# steel which is equal to 355 MPa. After 1 400 times of abrasive wear, a negative strain along the Z-axis is shown on the contact area of the U-shaped ring, and plastic deformation outward in both the X and Y directions is observed. The wear rate of U-shaped ring makes a cycle that repeats itself from large to small and then from small to large.

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Optimization Method of Power Supply Capacity of Distribution Network Considering Participation of Power Sales Companies in Spot Power Trading

ZHAO Qingsong, XU Jianyuan

2023, 43(4):  95-101.  doi:10.3969/j.issn.1008-0198.2023.04.014

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As an important part of the electricity trading market, the power sales companies can change the flow distribution of the distribution network by purchasing electricity from the market or delivering electricity to the market and users, thereby affecting the power supply capacity of the distribution network. Previous studies have rarely considered the impact of the uncertainty of power market trading on the operation of distribution networks when analyzing the power supply capacity of distribution networks. Based on the dual role of power sales companies, this paper first analyzes the interaction between market trading and distribution network power supply capacity. Secondly, considering the internal controllable distributed generation and controllable load participating demand-side response within the distribution network, a double-layer optimization model for distribution network power supply capacity considering power sales companies participating in electricity market spot trading is established, and it is solved based on the improved repetitive power flow algorithm and the original dual interior point method. Finally, the improved IEEE 33 test system is used to verify the algorithm, and the results show that power sales company participates in the power transaction by flexibly adjusting the power purchase and sale strategy, which not only ensures the profit but also improves the power supply capacity of the distribution net-work. This research can provide a theoretical basis for optimizing the configuration of the power market and improving the power supply capacity of the distribution network.

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Multi-Section Active Power Flow Control Algorithm Based on Multiple Regression Analysis and Iterative Linear Plan

YI Min, ZHAO Miao, ZHOU Hengyi

2023, 43(4):  102-107.  doi:10.3969/j.issn.1008-0198.2023.04.015

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A control algorithm based on multiple regression for multi-section active power flow is proposed in the paper.Firstly, the feature quantities with strong correlation with cross-section power flow are extracted.The Pearson correlation coefficient is used to calculate the correlation coefficient between the extracted feature quantity and the power flow of each section.According to the correlation coefficient, the extracted feature quantity is screened and multiple regression analysis is performed.Then, a multi-section power flow optimal control solution model is proposed.The model is used to calculate the adjustment amount of generator output for a given cross-sectional power flow adjustment.Finally, the proposed algorithm is verified using IEEE39 bus system, and the results show that the algorithm can not only accurately control the active power flow of multiple sections, but also calculate quickly.

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Analysis and Research on Influence of High Temperature and Dry Weather on Regional Power System in 2022 Summer

BIE Fangmei, FANG Rengcun, WAN Jing, FAN Yuhong, CHEN Xi

2023, 43(4):  108-113.  doi:10.3969/j.issn.1008-0198.2023.04.016

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In view of the difficulties and challenges faced by the power system during the extremely hot weather in summer in 2022, taking the operation of typical provincial power grids as an example, the maximum load, peak load duration and summer power grid load characteristics of the whole network are studied, and the outstanding problems in power supply during the summer vacation are analyzed, so as to put forward countermeasures and suggestions for how to ensure the safe and stable operation and reliable supply of the power system in summer.

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Case Analysis and Application of Waste Oil Disposal in Transformer

REN Qiaolin, ZHANG Yi, ZHANG Wei, CAI Xuan, WU You, LI Zhongling

2023, 43(4):  114-117.  doi:10.3969/j.issn.1008-0198.2023.04.017

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Taking the waste oil treatment of a power supply company as an example, the Meyers index classification and differentiation treatment of oil products are introduced, it not only reduces environmental pollution, but also extends the life cycle of transformer oil, saves the cost of oil treatment and new oil purchase, and promotes the utilization of renewable resources.

Faults and Analysis

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Research on Grounding Grid Corrosion Diagnosis Based on Electromagnetic Field Theory and Earth Surface Potential

CHU Xu, YU Shaoshuai, YAN Yabing, LI Hui

2023, 43(4):  118-124.  doi:10.3969/j.issn.1008-0198.2023.04.018

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Because of its large scale, complex structure and strong electromagnetic interference, the grounding grid of the substation has the problems of difficult detection and large error in corrosion diagnosis. Aiming at these problems,this article proposes a method based on the combination of electromagnetic field theory (EFT) and earth surface potential (ESP) to diagnose the corrosion conductor of grounding grid,so as to make up for the defect of poor measurement accuracy of EFT method under strong magnetic interference. This method first analyzes the magnetic induction intensity distribution of the corroded conductor on the basis of EFT. Then the paper analyzes the ESP distribution of the corroded conductor, combines the magnetic induction intensity curve with the ESP distribution curve, and finally determines the location and type of conductor corrosion. The test shows that the position of the corroded conductor obtained by this method is consistent with the position of the set corroded conductor, which shows the accuracy of the method in diagnosing the corroded conductor.

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Transformer Fault Diagnosis Method of Optimized Hybrid Kernel Extreme Learning Machine Based on Improved Northern Goshawk Optimization Algorithm

WANG Shibin, LI Duo, ZHAO Na, XIE Wenlong, HUANG Wei, JI Hongyu

2023, 43(4):  125-132.  doi:10.3969/j.issn.1008-0198.2023.04.019

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To improve the accuracy of transformer fault diagnosis, a transformer fault diagnosis method of optimized hybrid kernel extreme learning machine(HKELM)based on improved northern goshawk optimization algorithm(INGO) is proposed. Firstly, the ReliefF algorithm is used to filter and reduce the dimensionality of 19 dimensional transformer fault features. Secondly, three strategies of Logistic tent chaotic mapping, Cauchy mutation operator, and nonlinear increasing weight, are introduced to improve the Northern Hawk optimization algorithm and enhance its global optimization ability. Then, the improved INGO algorithm is used to optimize the initial parameters of HKELM to improve its classification accuracy and robustness. Finally, the features optimized by ReliefF are used as input features for the model and compared with different transformer fault diagnosis models. The simulation results show that the INGO-HKELM fault diagnosis model has higher fault diagnosis accuracy compared to other models.

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A Condition Estimation Method for DC-link Capacitors Based on Pre-charging Model

TIAN Rui, LIU Weike, WU Xun

2023, 43(4):  133-138.  doi:10.3969/j.issn.1008-0198.2023.04.020

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DC-link capacitors are key components for energy buffering in converter systems and are widely used in fields such as locomotive traction, aerospace, wind power generation and photovoltaic power generation. In harsh working environments, the performance of DC-link capacitors deteriorates, the failure rate increases, and they are easily damaged. Currently, the existing methods for state identifying of capacitors are easily affected by sensor measurement noise, resulting in a significant difference between the capacitance identification results and the actual values. To solve these problems, this paper proposes a capacitor state identification method based on the pre-charging process. By constructing the pre-charging model, the mapping relationship between capacitance and voltage signal is obtained, and the influence of measurement noise is minimized. Then, the recursive auxiliary variable least square method is used to estimate the parameters of the pre-charging model, so as to obtain the accurate capacitor capacity identification results. The verification results show that this method can effectively resist the interference of measurement noise, and has good identification effect when the signal sampling frequency is greater than 500 Hz. The capacitance identification error is 0.569% when the sampling frequency reaches 1 kHz.