Modeling Method And Comparative Study Of High Frequency Equivalent Circuit Model Of Lithium-ion Battery

Initially,lithium-ion batteries were widely used in electric vehicles due to their light weight,good cycle life,and high energy density.With the continuous development of lithium-ion batteries,they have gradually been applied to the rail transit field in recent years.In rail transit lithium-ion battery energy storage systems,the battery pack is usually connected to a DC-DC converter to control its energy flow.Because the DC-DC converter generates high-frequency noise and current ripple during operation,the lithium-ion battery is excited by high-frequency during the charging and discharging process.Therefore,studying the voltage response characteristics of lithium-ion batteries at high frequencies and establishing an accurate battery model are crucial to the design of battery management systems and DC-DC converters.In this paper,a high-frequency equivalent circuit model is established for the high-frequency characteristics of lithium-ion batteries,and different high-frequency models are compared and analyzed in the time domain and frequency domain.At the same time,the correlation between the ripple current frequency,ripple current amplitude,current rate and model parameters is analyzed.The electrochemical impedance spectroscopy test can obtain the internal information of the battery and the impedance information of the full frequency domain.By comparing the characteristics of each part of the impedance spectrum and the frequency response characteristics of electrical components,and combining with different electrochemical reaction processes of lithium-ion battery,the equivalent circuit model of the battery can be established in the frequency domain.In this paper,a fractional order high frequency equivalent circuit model is established by taking a typical electrochemical impedance spectroscopy as an example.And the discretization expression of the fractional order model in time domain is derived,which extends the fractional order model from frequency domain to time domain.In order to obtain high-frequency time-domain data,this paper builds a high-power high-frequency charge-discharge experiment platform with variable ripple parameters.The experimental platform is a hardware in the loop real-time simulation platform based on d SPACE,with DC-DC converter as the control object,and Go Online as the control logic,which realizes the functions of adjustable ripple current frequency,amplitude and current rate.In addition,using an industrial computer as a data acquisition platform,its higher sampling frequency can more accurately observe the current characteristics and battery voltage response at high frequencies.Finally,ignoring the low-frequency part of electrochemical impedance spectroscopy,five fractional high-frequency equivalent circuit models are established.The modified differential evolution algorithm is used to identify the parameters of the impedance spectroscopy,and the fitting accuracy of the five models is compared in different high-frequency ranges.The results show that the larger the high frequency range,the fewer models that can be accurately fitted.Then combined with the time-domain fitting results of the five models at 1k Hz,the applicability of different models in different frequency ranges is analyzed.In addition,by identifying the time-domain data under different current conditions,the influence of the frequency and amplitude of the ripple current and the current rate on the model parameters is analyzed.The results show that the model parameters have nothing to do with the ripple current frequency and amplitude,while the(RQC)element parameters are related to the current rate.From the fitting results of different ripple current frequencies,the fitting accuracy of time domain and frequency domain are consistent.