Design Of Battery Management System Based On SOC Estimation And Active Equalization

With the national efforts to promote the development of green transportation,new energy vehicles have been rapidly developed and popularized.Subsequently,the failure rate of electric vehicles is also increasing.The main cause of the failure is the failure of the power battery pack,so it is urgent to improve the design of the battery management system(BMS),in order to improve the accuracy of the real-time monitoring and regulation of the battery state,of which the estimation of the battery state of charge(SOC)and the battery pack balance are the two core technologies of the battery management system.In this thesis,the estimation of battery SOC and the improvement of battery pack active equalization technology based on SOC are studied.Finally,the hardware and software of BMS are designed.The main research contents are as follows:(1)Three common battery equivalent circuit models were compared and analyzed,and the equivalent circuit model of lithium-ion battery was established as second-order Thevenin equivalent circuit.The simulation results of the equivalent circuit model were in good agreement with the experimental results.Based on the equivalent model,the extended Kalman filter(EKF)algorithm was introduced to estimate the SOC of the battery based on the nonlinear characteristics of the battery performance.Under different operating conditions,the actual SOC values of the battery test are basically consistent with the estimated value curves obtained by the extended Kalman algorithm,which proves that the EKF algorithm can be applied to the estimation of SOC in BMS,and provides a basis for subsequent active equalization.(2)The concept of topological matrix T is proposed to analyze the active equalization of the battery pack,and on this basis,an active equalization circuit based on Buck-Boost bi-directional equalization control is designed.Fuzzy control was used as the balancing strategy,and the SOC estimated by EKF was used as the balancing criterion.The balancing current of each single cell in the battery pack was controlled to achieve the purpose of active balancing.The mathematical modeling was carried out on Matlab.The simulation results show that,whether static or dynamic balancing,the fuzzy control active balancing based on SOC can make the SOC of each single battery rapidly converge and improve the balancing ability.The bidirectional active balancing design of fuzzy control strategy can be applied to the development of actual battery management system.(3)The hardware design of the battery management system is carried out,and the design of balancing circuit,voltage and current detection and charging circuit on the control board is completed.On the basis of the hardware design,the software part is designed with C#,and the BMS object is finally obtained.After the system design and construction,the experimental test results show that,based on the monitoring of battery voltage,current and SOC by the upper computer,the characterization parameters of each single battery can be consistent through the equalization control,which improves the equalization control performance,thus verifying the function and reliability of the developed battery management system.