The Power Battery Model And SOC Estimation Algorithm Research Oriented To Pure Electric Vehicle Simulation

In recent years,with the shortage of energy and the increasingly-serious environmental situation,the automotive industry is studying the key technologies related to new energy vehicles on the world.Pure Electric Vehicle（EV）becomes one of the most concerned research directions.As the core component of EV,the battery management system（BMS）can guaranteed the driving safety and increase the range of electric vehicle as far as possible by the effective control and management of battery.It is still the important problem and difficulty to establish a battery model which can accurately describe the battery characteristics and to improve the estimation accuracy of the battery’s state of charge（SOC）in the BMS research.This thesis takes the LiFePO₄ battery as the research object.Based on the characteristics analysis of LiFePO₄ battery,an improved equivalent circuit battery modelis proposed.On the basis of considering the influence factors of SOC estimation accuracy,the extended Kalman filter（EKF）algorithm is proposed to improve the estimation accuracy.The main work is as follows:1.Characteristic analysis of LiFePO₄ battery.The internal structure,theworking principle,the performance parameters and the basic charge-discharge characteristics of LiFePO₄ battery are analyzed.During the charge-discharge period,the electro-chemical mechanism of the hysteretic voltage and the voltage rebound are emphatically analyzed.2.Modeling of power battery.The common battery models are analyzed and an improved equivalent circuit model is proposed for the electromotive force and the overpotential characteristics of the LiFePO₄ battery.The battery model is established with the Matlab/Simulink and the model parameters are identified by the test data.3.Estimation of SOC.The common SOC estimation algorithms are analyzed.Mainly based on the EKF algorithm,the influence factors are analyzed in the process of SOC estimation.The correction coefficients are set and the improved EKF algorithm is formed.The correction coefficients are determined by the experimental data and the simulation model is established with the Matlab/Simulink.4.Simulation and experimental verification.By using the testbed of the electric vehicle power system and taking three common automobile working conditions:European NEDC working condition,American UDDS working condition and typical urban working condition in China,the battery model and the improved EKF algorithm are simulated and verified.