Design And Improvement Of The Method For Estimating The Electric Quantity Of Lithium Battery

In the context of the development of the green concept,electric vehicles with lithium batteries as the main power source and new solar energy applications with lithium batteries as energy storage devices have been vigorously developed,making the application of lithium batteries more and more demanding.Accurately measuring the remaining power SOC of lithium batteries directly affects people’s travel safety and quality of life.Therefore,how to accurately estimate the remaining power of lithium batteries has become a contemporary research hotspot.There are three main reasons for the inaccuracy of power estimation.One is the equivalent circuit model representing the physical characteristics of the battery;the second is the influence of the battery’s working state on the parameters of the equivalent circuit model;the third is the accuracy of the battery’s working state on the SOC estimation Impact.In order to reduce the influence of these three aspects,the external characteristics of the lithium battery during the charging and discharging process were studied,and the second-order RC equivalent circuit model of the lithium battery was constructed.Through the constant capacity intermittent charge and discharge experiment,the model parameters of the lithium battery in the charging state and the discharging state were identified.The functional relationships between the open circuit voltage,ohmic resistance,concentration polarization resistance and capacitance,electrochemical polarization resistance and capacitance,and the remaining power SOC in the equivalent circuit model under charging and discharging conditions are established respectively.The main factors affecting the’ SOC estimation of lithium batteries are analyzed.Based on the research of the extended Kalman filter method(EKF),a second-order EKF algorithm is adopted,and a combination of ampere-hour integration method and open circuit voltage method is designed to improve the SOC estimation.The precision method is the improved extended Kalman filtering algorithm.Combining the result of model parameter identification with the improved extended Kalman filter algorithm,the SOC of the remaining power of the lithium battery in the charging and discharging state is estimated separately.The model parameters of the lithium battery are obtained through experimental parameters and fitting methods.Completed the estimation of the remaining power SOC under constant current charge and discharge and pulse charge and discharge conditions.Experimental results show that the maximum error of SOC estimation under constant current conditions does not exceed 2.6%;the maximum error of SOC estimation under pulse conditions does not exceed 3%.The experimental results prove the accuracy of the model parameters and the effectiveness of the designed SOC estimation method,which improves the estimation accuracy of the remaining power SOC of the lithium battery.