Research On State Of Health Estimation Of Electric Vehicle Lithium Power Battery

In the "13th Five-Year Plan" national key research and development projects of Auto-related industry,the direction of the new energy vehicles focused on the power battery,battery management system as well as six technical directions.The study of the State of Health(SOH)estimation,which is one of the important aspects of the battery management system(BMS),lags far behind the state of charge(SOC)and balance control research.Accurate real-time estimation of battery SOH plays an important role for the balance control research system and extend the mileage of electric vehicle.It also ensures the safety of the battery significantly.In this paper,to estimate electric vehicle power lithium-ion battery SOH done the following work:First defines the definition of SOH,divides into off-line estimation method and the online estimation method and introduced the common SOH estimation methods.The seven battery performance indexes with large influence of SOH were studied.Based on these factors,the influencing factors of SOH were summarized,and four measures to extend battery aging were put forward.The Thevenin equivalent circuit model is selected as the basic battery model for SOH estimation based on the requirements of cost and estimation accuracy.Designed experiment uses the fast standing and multiple measurements to reduce the error,calibrated the SOC-OCV curve,fits the RC parameters in the equivalent circuit model by exponential fitting,and validates the parameters accuracy using the random excitation current simulation experiment.Based on the principle that the capacity is a slow change parameter,a battery capacity model for SOH estimation is established.An accurate estimate of SOC is an prerequisite for estimating SOH.Estimated SOC by using the extended Kalman filter method based on the Ansonia integral method and the SOH is estimated by Kalman filter based on the capacity method.Finally,the system state equation and system observation equations based on SOC and capacity are established.The capacity of the current time of the battery is estimated by using the double extended Kalman filter method,and the SOH is calculated by the capacity calculation.The experimental results show that the effect is good and the SOH is estimated well.The accuracy error is within 1%.By analyzing the simulation results of dual Kalman filter,the basic requirements of SOH estimation circuit board are obtained.The hardware circuit and its supporting software of SOH estimation are designed.The hardware circuit mainly includes The circuit for the system to provide the appropriate voltage,as well as the voltage and temperature measurement circuit,communication circuit and its peripheral circuit,The final measured voltage and current temperature and the estimated SOH are displayed on the display screen.Based on the SOH estimation hardware and dual Kalman filter method,the framework of the system software is analyzed,and the system initialization and parameter setting are designed in a modular design.After the circuit board is finished,the hardware and software verification circuit based on the battery test box are designed.The accuracy error is controlled within 1%,the robustness is good and the result is stable and reliable.