Research On Estimation Method For SOC Of Lithium-ion Batteries

With the increasing use of lithium-ion batteries,research on their management is getting deeper and deeper.Lithium-ion battery state of charge?SOC?is usually defined as the ratio of available battery capacity to rated capacity.It acts as an important state quantity of the battery to help managers or users understand the available battery power in real time and predict its energy output.It also helps prevent overcharging or overdischarging of the battery,ensuring safe use and prolonged service life.Lithium-ion batteries are a complex nonlinear time-varying electrochemical system.The SOC cannot be directly observed and can only be estimated indirectly by control quantities and observable measurements.Therefore,how to use the control quantity and observable measurement of lithium-ion battery for accurate real-time estimation of SOC has become an important research topic,with important theoretical research and engineering practical significance.Firstly,the background and significance of the research are introduced.The research status of SOC estimation methods for lithium-ion batteries at home and abroad is summarized,and the research content of the subject is clarified.Secondly,the structure and working principle of lithium-ion batteries are analyzed,the definition of SOC of lithium-ion batteries and the expression of its ampere-time integral are briefly described,the battery charging and discharging experimental system is designed and built,and the related charging and discharging experiments are carried out.According to the experimental results,the characteristics and charging and discharging efficiency of lithium-ion batteries are analyzed andThirdly,based on the analysis of common equivalent circuit models of lithium-ion batteries,the second-order RC model is selected as the battery SOC estimation model,and the second-order RC model is parameter-identified according to the battery charging and discharging experimental data.The battery model was built in MATLAB/Simulink environment,and the model was identified by battery discharge experimental data.The accuracy of the second-order RC model and the validity of parameter identification were verified.Fourthly,based on the analysis of extended Kalman filter?EKF?and approximate second-order extended Kalman filter?ASEKF?,the state equations of lithium-ion batteries with SOC,RC branch voltageU₁ andU₂ as state variables are established based on the second-order RC model of lithium-ion batteries,and the estimation methods of SOC for lithium-ion batteries based on EKF and ASEKF are studied respectively.The SOC estimation model is built in MATLAB/Simulink and simulated.The simulation results show that both EKF algorithm and ASEKF algorithm can accurately estimate the SOC of lithium-ion batteries,but compared with ASEKF,the SOC estimation method based on ASEKF has higher accuracy and better convergence.Finally,a SOC estimation system for lithium-ion batteries based on DSP is designed.The SIL test,PIL test and HIL test of the SOC estimation method based on ASEKF are carried out.The experimental results show that the SOC estimation system based on DSP runs stably and can accurately estimate the SOC of lithium-ion batteries in real time.