Research On The State-of-charge Estimation Of Lithium-ion Batteries

The development and application of new energy electric vehicles have alleviated the energy shortage and environmental pollution to a certain extent,but there are still many technical problems to be solved urgently in the process of industrialization,such as improving the endurance mileage,increasing battery life,improving vehicle performance,etc.The main methods to solve the above problems are: to develop battery technology to find appropriate power battery technology solutions,and to improve the battery management system(BMS)to give full play to the best performance of power batteries.The state of charge(SOC)estimation of batteries is the core and key technology of BMS.In order to study the accurate estimation method of SOC,this paper takes the ternary lithium-ion batteries with high energy density as the research object,puts forward the SOC estimation method using 2RC-Thevenin equivalent circuit model and ASRUKF algorithm,and carries out the corresponding simulation and experiment.The specific research contents are as follows:Firstly,the development status of electric vehicle is briefly introduced.The working principle and related technical parameters of lithium-ion battery are analyzed.The charging and discharging characteristics,rate characteristics,temperature characteristics and cycle characteristics of the selected ternary lithium-ion battery are tested.Secondly,the commonly used battery models are compared.Considering the accuracy,complexity and computational complexity,the 2RC-Thevenin equivalent circuit model is selected as the research model of ternary lithium-ion battery.The parameters of the circuit model and OCV-SOC curve are identified and fitted by pulse discharge experiment,and the accuracy of parameter identification is verified in the battery simulation of MATLAB/Simulink.In order to improve the negative covariance of UKF algorithm and reduce the interference of uncertain noise in the process of SOC estimation,the idea of Sage-Husa adaptive algorithm and square-root filter is introduced based on UKF algorithm.An Adaptive Square-Root Unscented Kalman Filter(ASRUKF)algorithm is formed,and the correction factors such as temperature and cycle life are added to the SOC estimation algorithm.The three algorithms of EKF,UKF and ASRUKF are simulated and compared under four different conditions: constant current discharge,constant current charging,pulse discharge and DST.The simulation results show that ASRUKF algorithm has higher accuracy,better stability and faster convergence speed than the other two.To verify the estimation accuracy of ASRUKF algorithm based on 2RC-Thevenin equivalent circuit model,the experimental platform of SOC estimation is built by using dSPACE MicroLabBox.The experimental verification of SOC estimation for ternary lithium-ion battery under constant current discharge and constant voltage charging is carried out.The experimental results show that the ASRUKF algorithm can converge steadily and rapidly with an error of less than 1.5%.