Research On Modeling And SOC Estimation Of LiFePO₄ Battery Considering Temperature Effect

LiFePO₄ battery,which has a small size,long life,can be large current discharge and maintenance-free.It has been widely used in electric vehicles,communications tools,energy storage systems and other fields.At present,LiFePO₄ batteries,as the power source of pure electric vehicles,are most often used in such occasions.And as the core components of electric vehicles,its performance affects the vehicle performance.The SOC of power battery is an important parameter of electric vehicles,reflecting the amount of its remaining power.In the process of driving,ambient temperature has a great influence on the battery,and thus affects the estimated accuracy of the battery SOC.Therefore,the efficient management of these batteries,accurate prediction of the actual operation of the battery SOC,can be more efficient battery and vehicle management,to predict the mileage of electric vehicles.It has important significance onthe use and maintenance of the battery pack.The application background of LiFePO₄ battery in pure electric vehicle,its electrochemical principle and working characteristics are introduced at first,and the factors that affect the performance of the battery are analyzed.The battery model used in this dissertation is then selected by analyzing and comparing the conventional battery models.Aiming at the problem that the SOC of LiFePO₄ battery is influenced by the ambient temperature,a new type of battery modeling method based on Nernst electrochemical equation is proposed by analyzing and comparing.The experimental data are applied to the statistical design of experiment?DOE?.A more accurate battery internal resistance model is obtained by measuring less data,and the other parameters in the model can be fitted with the continuous change of the temperature and the battery SOC at different time to realize the real-time estimation of the entire battery model.Finally,the extended Kalman filter?EKF?algorithm is introduced.The state space equation of the LiFePO₄ battery based on the modified Nernst battery model is analyzed.Under the laboratory conditions,the charge and discharge experiments at different temperatures and different working conditions are carried out.And the EKF model of SOC estimated in the MATLAB / Simulink module is used to simulate the experimental data.The dynamic estimation of the SOC of the lithium battery is realized.The error between the improved battery model and the traditional battery model in the SOC estimation is compared.The results show that improved Nernst battery model can achieve higher SOC estimation accuracy.