Study On State Of Charge Estimation And Thermal Performance Of Power Lithium Batteries

In order to alleviate energy resources and ecological environment's enormous pressure caused by automobile industry,the rapid development of electric vehicles has become a strategic measure in various countries.As the core technology of electric vehicle,the estimation of state of charge(SOC)and the thermal management of battery in power battery system are key indexes,which affect the endurance,cost and safety of electric vehicle.This paper focuses on the two core parts of the power battery system-“electricity and heat”.A second-order equivalent circuit model and an electrochemical-thermal coupling model of the cylindrical 18650 ternary lithium-ion battery were established.In addition,Lithium-ion battery open circuit voltage test,maximum capacity and custom dynamic condition test were conducted.Based on the above model and experiment,this paper estimates the state of charge of the lithium ion battery for vehicle and researches on the thermal performance of the lithium ion battery.This paper briefly introduces the research background and summarizes the development history of electric vehicles.It is pointed out that lithium ion batteries are ideal vehicle power batteries by comparing advantages and disadvantages of several commonly used power batteries.This paper further analyzes the working principle of lithium-ion batteries and several commonly used modeling methods.The current state of research on the SOC estimation and the thermal performance of the battery during discharge were listed in this paper.On the basis of the experimental data of lithium ion battery extracted from National Aeronautics and Space Administration(NASA),the off-line SOC estimation of the lithium battery with the back propagation(BP)neural network model optimized by genetic algorithm(GA)were completed.The results show that the maximum estimated error of SOC is 4.21% and the average absolute error is 1.70%.This paper introduces the uncharged Kalman filter(UKF)method to estimate the SOC of the lithium-ion battery.This method can realize on-line identification of parameters in the second-order RC equivalent circuit model of lithium battery by the improved least squares algorithm and then applies the identified parameters to the SOC estimation.The results show the maximum estimation error is 4.94% and the average absolute error is 1.43% with the method.Finally,this paper establishes the electrochemical-thermal coupling model of ternary lithium battery,the accuracy of the model was verified by charging and discharging experiments.Simulation results of lithium battery thermal performance under different discharge rates,ambient temperatures and convective surface coefficients were analyzed,which provide theoretical basis for the design of thermal lithium battery thermal management system.