Research On Equivalent Circuit Model Of Lithium Ion Battery Based On Electrochemical Impedance Spectroscopy And Estimation Of State Of Charge

Recently,with the deterioration of global climate and the response of local governments to policies,electric vehicles have developed rapidly due to their advantages of zero pollution,zero emissions,and low noise,but there are still many problems such as short mileage and poor security and so on.As the power source and core component of electric vehicles,lithium-ion battery’s accurate modeling is crucial for the battery management system to monitor and complete accurate state estimation in real time.To this end,this article takes lithium iron phosphate battery with the best safety performance at present as the research object and uses electrochemical impedance spectroscopy（EIS）technology,a non-destructive measurement of electrochemical testing technology,to establish a second-order equivalent circuit model,which can reflect the battery internal electrochemical reaction information.And based on the model,it can accurately estimate the State of Charge（SOC）of the battery,which provides effective data accumulation and theoretical method for lithium ion battery modeling and state estimation.In this research,firstly,electrochemical impedance spectroscopy and equivalent circuit model theory have been regarded research basis,the battery charging and discharging test system,an electrochemical workstation,a temperature recorder,and a thermostat have been used to establish an experimental bench.Under the full temperature range（-10°C,0°C,10°C,25°C,40℃）and full SOC range（0%-100%）,the maximum available capacity test,U_OC-SOC curve test,and DST test were performed on the lithium iron phosphate battery.Then,through the analysis of electrochemical impedance spectroscopy,an equivalent circuit model based on the internal mechanism of the battery was established,and the physical meaning of the model and model parameters was clarified.After multiple fittings of the measured 55 EIS and simulation verification of pulse discharge,the validity and accuracy of the model are proved.Then,by fitting the calculated model parameters at different temperatures and SOCs,a database is established to study the variation between each model parameter and temperature/SOC.Through the parameters such as ohmic internal resistance and charge transfer internal resistance,the change process of the internal electrochemical reaction of the battery with temperature and SOC is revealed.Finally,the extended Kalman filtering algorithm is studied,and the algorithm is combined with the built model to establish the system space equation.The SOC estimation process is designed,and the estimation is completed on the Simulink simulation platform.The estimation error is within 2%,the results show that the method has good estimation accuracy.The research in this paper shows that the equivalent circuit model based on electrochemical impedance spectroscopy is a fusion of the physical meaning of electrochemical reactions with the characteristics of simple and easy calculation of equivalent circuits.It can accurately simulate the dynamic characteristics of the battery,and this model combined with the extended Kalman filter algorithm also has a higher accuracy for battery SOC estimation,which lays the foundation for effective management and accurate prediction of the battery management system.