Research On State Of Charge Estimation And Equalization Technique Of Electric Vehicle Power Battery

In recent years,China's electric vehicle industry has developed rapidly,as one of the three core technologies of electric vehicles,battery management technology has also become a hot topic of research.This dissertation mainly studies the state of charge(SOC)estimation and active equalization control technology in the battery management system(BMS)of electric vehicles.The SOC estimation method based on DEKF algorithm is used to improve the accuracy of the battery state of charge estimation and prevent damage to the battery pack from overcharge or overdischarge.Based on the working principle of the flyback transformer,an active equalization topology and balanced control strategy are designed to give a good balanced control of each cell of the power battery pack,so that all the cells in the battery pack maintain good consistency and prolong the driving of the vehicle mileage and battery life,give full play to the battery performance.The specific work is summarized as follows:(1)Power battery basic characteristics analysis.First of all,the working principle and voltage characteristics,internal resistance characteristics and capacity characteristics of the lithium-ion battery in this study are analyzed,which provides reference for the following SOC estimation and balanced control technology research.(2)Power battery equivalent circuit modeling and battery parameter identification.Based on the comparative analysis of the modeling method of the power battery,built the 2-order RC equivalent circuit model of the battery.The parameters of the battery under different states of charge are identified by means of off-line identification and on-line identification respectively.Finally,the accuracy of on-line identification is proved by model simulation.This model provides a control object and simulation platform for the accuracy verification of the subsequent SOC estimation algorithm and the verification of the effects of the equalization control.(3)Study on estimating methods of the battery's SOC.In this dissertation,the estimation method based on double Kalman filter(DEKF)is designed to solve the problems such as the error accumulation in the traditional Ah integration method(Ah)and the difficulty of parameter identification in the extended Kalman filter(EKF)algorithm.The algorithm design and simulation verification is completed in Matlab platform,which proves the superiority of SOC estimation method based on DEKF algorithm.(4)Study on active equalization control technology of EV battery pack.Firstly,the working principle of the balancing circuit based on the flyback transformer and the related parameter design method are analyzed.Then the equalization starting criterion is determined and the equalization starting threshold is set.Finally,the equilibrium control strategy is formulated.The simulation results show that the active equalization control system can maintain the consistency of the battery pack in charge,discharge and hold state.