Study On SOC Prediction Method Of Lithium Iron Phosphate Battery Based On Modified Thevenin Model

The performance of hybrid armored vehicles can be used as a standard to measure the level of a country’s operations.In recent years, lithium iron phosphate battery has been paid more and more attention because of its high specific energy and safety.The remaining power of lithium iron battery is the primary research problem of battery management system and has great significance to improve the vehicle performance of armored vehicles.The purpose of this paper is to study a method of on-line measurement of battery SOC, mainly from two aspects of research model and estimation method of battery.By comparing with the commonly used battery model,the paper uses a wide range of Thevenin model.In order to better simulate the chemical reaction of battery, a RC loop is added on the basis of the Thevenin model and the parameters of the model are identified by the HPPC experiment.Then voltage simulation model is built in Matlab/Simulink.The modified model is validated in the constant current pulse condition.The simulation results show that error of the improved model is smaller than the original model.The average error of the improved model is 0.01 V, and the original model is 0.04 V, which shows that the improved model has higher accuracy.Determining the model, the results of model parameters identification and the initial voltage determined by open circuit voltage method are taken into extended Kalman filter(EKF) to predict SOC.Then a battery simulation model is built in Simulink,and the input is the battery load voltage and current,output for SOC of the battery and the measurement noise covariance.Bringing the experimental data into the model. Finally compared with EKF estimation results and simulation results, it can be seen that the SOC estimate can fast convergence to the theoretical value, and fluctuating near the theoretical value,and SOC estimation precision is within 5%, which shows that the model and algorithm can be used in a real reflect the working state of the armored vehicle, meeting the test requirement.The software and hardware of SOC estimation are also designed. The hardware is mainly the design of the current and voltage storage test device which has the advantages of anti interference, electromagnetic shielding, strong stability, data is not easy to lose.The software is the software design of acquisition device and estimation system.