SOC Estimation Based On Thermo-Electric Model Of Li-Ion Battery Pack

In recent years,China’s electric vehicle industry has entered a period of rapid growth from the introduction period.The Battery Management System(BMS)undertakes the mission of efficient,safe and long-life operation of electric vehicles.As the core function of BMS,the estimation of the remaining battery capacity(SOC)provides an important basis for the energy and safety management of electric vehicles.However,the estimation accuracy is affected by two main factors,one is due to the limitation of electrode potential and material,the voltage and capacity of the single battery can not fully attain the energy requirements of the electric vehicle,and a large number of batteries must be connected in series and parallel to form the power battery pack,but there is inconsistency in the parameters of the battery in the production and use process,which will lead to obvious differences between the batteries;The second is that the battery pack will generate heat during the working process,and the heat that has not been released in time is absorbed by the battery itself,resulting in an increase in the working temperature,and the temperature will further affect the battery parameters.Therefore,a Improved Mean-Difference Method(IMDM)was proposed to estimate SOC of power battery packs by considering the inconsistency of battery packs and the change of battery operating temperature.The main research contents of this paper are as follows:(1)Research on the working principle and electrical characteristics and thermal characteristics of lithium-ion batteries.Taking lithium-ion batteries as the research object,this paper analyzes the influencing factors of the performance of single cells and battery packs,explores the heat generation and transfer characteristics of lithium-ion batteries,and establishes a foundation for building a thermoelectric coupling model.(2)Establishment of thermoelectric coupling model and parameter identification.Based on the in-depth analysis of the heat generation and transfer characteristics of lithium-ion batteries,a thermoelectric coupling model is established to enable the parameters of the equivalent circuit model and the thermal model to be transferred and coupled with each other.Through the battery experimental dataset disclosed by Calce,the two identification algorithms of COA(Coyote Optimization Algorithm)and FFRLS(Forgetting Factor Recursive Least Square)were applied to the parameter identification of the thermoelectric coupling model,which met the requirements of model parameter accuracy.(3)SOC estimation method for single lithium-ion battery.In this paper,Improved Sage-Husa Adaptive Extended Kalman Filter(ISH-AEKF)was combined with the thermoelectric coupling model,and the core temperature,surface temperature and SOC of single lithium-ion battery were estimated at the same time.The difference between the measured surface temperature and measured voltage of battery was used to modify the model parameters.The error of SOC estimation caused by the deviation between temperature change and initial SOC value is solved.The accuracy and robustness of the proposed method are verified by simulation experiments.(4)Lithium-ion battery pack SOC estimation method.In order to solve the problem of inconsistency and operating temperature variation in battery packs,the thermoelectric coupling model is applied to the mean difference method to estimate the SOC of battery packs.By setting up a charge-discharge test platform and verifying the method based on the measured data,the experimental results show that the proposed method has a high accuracy in estimating the battery pack SOC.