Research On Equalization Control Strategy Of Electric Vehicle Battery Pack Based On State Of Charge Estimation

In recent years,in response to the problems of energy crisis,environmental pollution and climate warming,electric vehicles have become the main development trend in the automotive field.The power battery pack of electric vehicle is composed of several single batteries in series or in parallel to meet the voltage,power and energy requirements of electric vehicles.However,the inconsistency of the single battery is caused by the difference in manufacturing and using process,which affects the range and safety of electric vehicles.Therefore,in this paper,the equalization control based on the estimation of the state of charge of the battery is carried out to reduce the inconsistency of the battery pack.First of all,this paper analyzes the advantages and disadvantages of different equalization circuits.Based on the distributed non-dissipative equalization circuit,an improved Buck-Boost equalization circuit is designed,which makes the series batteries form a ring-shaped energy loop,and transfers energy through the optimal equalization path to reduce the equalization time.Secondly,this paper introduces the characteristics of the existing battery model,selects the second order RC equivalent circuit model to establish the single battery model,completes the open circuit voltage(OCV)-state of charge(SOC)curve fitting and resistance and capacitance parameters identification through experiments.In this paper,the SOC of battery is selected as the equalization variable,and back propagation(BP)neural network algorithm is used to estimate the SOC.Then,this paper proposes an equalization control algorithm based on SOC,which is composed of the following two parts:the first part is the energy path optimization algorithm based on particle swarm optimization(PSO),which can find the optimal energy path of battery equalization to improve the energy utilization rate;the other part is the variable universe fuzzy logic control algorithm based on fuzzy inference,which can realize the dynamic adjustment of the equalization current to reduce the time consumption.Finally,the battery equalization system is built in MATLAB/Simulink.The simulation results show that the improved Buck-Boost equalization circuit can shorten the equalization time by 26%;the energy path optimization algorithm based on PSO can reduce the energy loss by 2.02%;the variable universe fuzzy logic control algorithm based on fuzzy inference can shorten the equalization time by 31%compared with the traditional fuzzy logic control algorithm.The proposed equalization scheme reduces the time consumption,improves the energy utilization rate,and effectively reduces the inconsistency of battery pack.