Research On SOC Estimation And Balance Control Of Lithium-ion Battery For Electric Vehicle

Recently,as countries around the world begin to set up carbon neutrality goals to respond to the challenges of climate change.And the development of electric vehicles is just one of the important measures for the automobile industry to achieve carbon neutrality.China’s electric vehicle industry is also developing rapidly in this context,and the speed of technological update and iteration is also accelerating.The battery management system(BMS)connects the power battery and the electric vehicle,and is also the link between the power battery and the electric vehicle.Among them,State of Charge(SOC)estimation and equalization control technology are the research emphases in BMS.Accurate SOC estimation is of great significance for extending battery life,optimizing battery management system and ensuring the safe operation of electric vehicles.The fast and efficient equalization control can maintain the energy balance of the battery,prolong the battery life and improve the safety of the battery system.This paper studies the SOC estimation and equalization control of lithium-ion batteries.The specific works are as follows:(1)Working principle and characteristic analysis of lithium-ion battery.This paper analyzed the advantages of lithium-ion batteries,compared the characteristics of different types of lithium-ion batteries,and studied the working characteristics of the selected lithium-ion batteries,such as voltage characteristics,internal resistance characteristics and capacity characteristics,so as to provide data support for subsequent SOC estimation and balance control research.(2)Modeling and parameter identification of lithium-ion battery.This paper analyzed several common battery models.Suitable and simple second-order RC equivalent circuit model was selected for research,and the battery model parameters were identified using offline identification method.As offline identification method cannot be used online,an online parameter identification method using recursive least squares method with forgetting factor(FFRLS)was proposed to identify model parameters,which provided an accurate model basis for subsequent SOC estimation and balance control research.(3)Study on SOC estimation of lithium-ion battery.This paper studied the principle of classical Kalman filter,and introduced singular value decomposition to solve the problem of negative determination of error covariance matrix in unscented Kalman filter algorithm.Because of the low accuracy problem caused by unknown prior statistics of system noise,a CA-SVDUKF algorithm based on covariance adaptation was proposed to estimate SOC.The traditional extended Kalman filter,unscented Kalman filter and the proposed algorithm were verified under different working conditions,and it was proved that the proposed algorithm had high accuracy and anti-interference ability.(4)Research on the balance control of lithium-ion battery pack based on SOC.This paper analyzed and compared various equalization topologies,proposed an active equalization topology based on flyback transformer,developed corresponding equalization strategies,and verified the effectiveness of the equalization scheme under the three different working conditions of lithium-ion battery charging,discharging and shelving under simulation conditions.The results showed that the equalization scheme had high efficiency and could effectively improve the consistency of the battery pack.