Joint Estimation Of SOC And SOP For Traction Power Battery In Electric Vehicles

Peak power is the major parameter for acceleration,climbing,and energy recovery,which is an important performance for electric vehicles(EV).The traditional method estimating peak power is based on calibration method,which fails to consider the influence of polarization effects and leads to large estimation results,and there are problems such as long test period,large workload,and high equipment requirements,which restricts the development of the battery management system.Considering the close relationship between the SOC(state of charge)and SOP(state of power),joint estimation of SOC and SOP was adopted in this thesis,The main work is as follows:The ternary material lithium-ion battery was selected for research,in order to grasp the performance of the battery.Some basic performance tests under different temperatures,different discharge rates and different power were couducted based on the battery test platform.Subsequently,two low-order equivalent circuit models were established to evaluate model accuracy and evaluation perfermance difference.The HPPC(hybrid pulse power charateristics)tests were used to identify the battery parameters,and the battery polarization characteristics were analyzed.Based on the charge and discharge characteristics of the battery,considering the deficiency of single parameter constrained SOP estimation and the inherent relationship between SOC and SOP,the peak power estimation method based on DP battery model and multi-parameter constrains was proposed and the related equations were introduced.SOC and SOP joint estimation model was established based on the EKF algorithm and validated experimentally.The SOC and SOP estimation accuracy and estimation perfermance were analysed.The results show that:(1)Low temperature has a significant effect on battery performance.The discharge capacity and discharge platform decreased significantly in low temperature;high temperature,the rate of discharge and power of discharge have little effects on the battery capacity;The discharge energy decreases as the discharge power increases.(2)The polarization voltage has a plateau in high and middle SOC,which increases obviously in low SOC.The polarization voltage during the discharge process is higher than that during the charging process;the polarization voltage is obviously increased and the plateau period is shortened at low temperature;the rate of discharge is larger and the polarization effect is greater.(3)The estimated voltage based on Dual Polarization(DP)model has small error and the SOC estimation maximum error based on low-order equivalent circuit models is less than 3%,but the maximum error based on the DP model is about 2%,which is better than the Thevenin model.(4)The maximum error of peak power estimation with the SOC and SOP joint estimation based on DP model is less than 3%,which is smaller than that with the Thevenin model;The longer the discharge duration with peak power,the smaller the peak power value.The SOC and SOP can rapidly converge to the accurate values when initial SOC has errors.