Li-ion Battery Modeling And SOC Estimation Based On Equivalent Circuit And Simplified Electrochemical Model

Lithium-ion batteries are widely used in plug-in hybrid electric vehicles and pure battery electric vehicles due to their high voltage,large specific energy,long life and low self-discharge rate.In order to ensure the safe and stable operation of lithium-ion batteries,a accurate battery management system(Battery Management System,BMS)to provide real-time battery status.The battery state of charge(SOC)not only provides information on the remaining available capacity,but also indicates the charging and discharging strategy,which has a significant impact on the performance and life of the battery,and model-based SOC estimation has become mainstream.To this end,this paper takes the ternary material lithium-ion power battery as an example,and conducts the following research on the common equivalent circuit model and simplified electrochemical model of the battery as well as the SOC estimation based on the model:Firstly,the experimental scheme of lithium-ion battery is introduced,and the basic characteristics of ternary lithium-ion power battery with rated capacity of2500 mah and nominal voltage of 3.7V are analyzed.Considering the accuracy and complexity,a second-order equivalent circuit model is selected,the state space equation of the second-order equivalent circuit model is deduced and discretized,and battery parameters are obtained by offline parameter identification experiments.Secondly,three SOC algorithms,Ampere-hour integral method(Ah),Extended Kalman Filter(EKF)and Dual Extended Kalman Filter(DEKF),are introduced.The robustness of the three SOC estimation algorithms is compared from the four scenarios of initial SOC error,parameter identification error,current sensor error and voltage sensor error,and it is concluded that the DEKF algorithm has strong robustness and higher SOC.Estimation accuracy,the absolute value of SOC estimation error is within 3%,and the convergence speed is within 100 s.After that,the five processes of solid-phase diffusion,liquid-phase diffusion,solid-phase potential distribution,liquid-phase potential distribution,and Butler-Volmer were introduced in detail,and the five processes were simplified to obtain an extended single process.The particle model(Extended Single Model,ESP)was verified,and the model accuracy before and after the simplification was verified.The maximum error of the simplified electrochemical model was 30 m V.Finally,based on the charging and discharging data of the battery experiment,many parameters of the simplified electrochemical model are identified separately.First,the lithium intercalation interval of the positive and negative electrodes is identified based on the double water tank model,and then the sensitivity analysis of the remaining parameters is carried out,and the high sensitivity is selected.Based on the simplified electrochemical model,the closed-loop SOC estimation algorithm is proposed and verified.The accuracy of the simplified electrochemical model is within30 m V,and the maximum error of SOC estimation is about 3%.