Research On State Of Charge Estimation And Equalization Technology For Battery Management System

In electric vehicles,Battery Management System(BMS),as the link between the battery and the vehicle system,plays a huge role in ensuring the reliable operation of the battery and improving the safety performance and range of electric vehicles.The problem of low accuracy of SOC estimation and battery inconsistency has become a bottleneck to the development of BMS.In this paper,a SOC estimation method based on Extended Kalman Filter(EKF)and an active equalization scheme based on a bi-directional flyback converter topology are investigated to improve the estimation accuracy and equalization efficiency of the BMS.The main work of this paper is as follows:(1)A lithium-ion battery modeling study is carried out to provide a battery model basis for the EKF algorithm.A second-order RC equivalent circuit is used to model the battery,and the offline identification of the battery model parameters is completed based on the Hybrid Pulse Power Characteristic(HPPC)test data.The accuracy of the battery model is verified by simulation,and the simulation results show that the identification of the battery model parameters is accurate and the model has high accuracy.(2)The battery SOC is estimated by an EKF algorithm based on the second-order RC model.Simulation experiments of SOC estimation based on EKF algorithm are carried out to verify the estimation performance of EKF algorithm.The simulation results show that the EKF algorithm has high estimation accuracy.(3)A study on the active equalization system for Li-ion batteries was conducted.The system combines a bi-directional flyback converter-based equalization topology and a charge/discharge equalization strategy to achieve battery pack voltage consistency The operating mode,control method and circuit parameters of the equalization topology are designed in detail,and the rationality of the design is verified by simulation.(4)The BMS management system of a 12-cell Li-ion battery was built.and the experimental study of SOC estimation method and equalization system was carried out.SOC estimation experiments,equalization topology performance and equalization strategy feasibility verification experiments were conducted.The experimental results show that the maximum SOC estimation error of the EKF algorithm is less than 5%,and the active equalization scheme can control the voltage polarity at the end of charging and discharging of the battery pack to 2m V and 4m V,respectively.The SOC estimation method and active equalization scheme can improve the SOC estimation accuracy and equalization efficiency of the BMS.