SOC Estimation Of Lithium Batteries For Electric Vehicles And Equalization Technology Research

In recent years,with the improvement of people's living standards,cars have gradually become an indispensable tool for people's daily travel.However,the large consumption of fossil energy has seriously polluted and damaged the air environment around people,and even threatened their physical and mental health.With the continuous change of the energy structure,new energy pure electric vehicles with power battery packs as the energy core have become the mainstream of China's future automotive industry development due to the advantages of energy saving and almost zero emissions.Lithium batteries have become the first choice for electric vehicle power battery materials due to their high energy density,low self-discharge rate,long cycle life,and better safety performance.In order to better improve the cycle life of the power battery pack,increase the cruising range of the vehicle,and at the same time ensure the safety of the battery pack,it is very important to have an excellent Battery Management System(BMS).This article focuses on the main problems in the current development of electric vehicles.Taking ternary lithium batteries as research objects,the two main issues of state of charge(SOC)estimation and energy imbalance of power lithium batteries are solved.The main research contents are as follows:(1)Establishment of equivalent model of lithium battery and parameter identification.Analyze the working mechanism of lithium battery,take the second-order RC equivalent circuit model as the research object in this paper,identify the model parameters based on the HPPC(Hybrid Pulse Power Characterization,HPPC)experimental principle,and verify the model in Matlab simulation environment Simulation accuracy and timeliness.Then analyze the causes and effects of the energy inconsistency of the lithium battery pack,determine the key factors of the equilibrium strategy and the choice of variables.An excellent energy balance control system should have the advantages of fast equalizationrate,energy balance between non-adjacent cells,The choice of equilibrium variable is subject to SOC.(2)An algorithm based on Unscented Kalman Filter(UKF)is proposed to estimate the battery SOC value.First analyze the UKF algorithm,take current and other variables as the system input,write a simulation program for verification in Matlab environment,and perform the evaluation with the A-time integration method and Extended Kalman filter(EKF)algorithm.The results show that the UKF algorithm has better estimation accuracy.(3)An energy balance control scheme for lithium battery based on energy conversion strategy is proposed.The inductance is used as the energy carrier,and the range of the SOC between the cells is used as the basis for judging whether the equalization system is turned on.The proposed equilibrium control strategy is simulated and analyzed.The main advantage of this balancing strategy is the ability to quickly equalize and achieve energy balancing between non-adjacent single cells.As the battery ages,capacity decays and internal resistance become large,the balancing rate will increase.