The Battery SOC Estimation Of College Students' Pure Electric Formula

State of Charge(SOC)is an important parameter in the battery management system(BMS)which guarantees the best performance and security,and the directreflection of battery capacity.On one hand,it provides the driving range information tothe driver,on the other hand,it provides the related information for management and maintenance of BMS.Therefor,accurate SOC estimation is indispensable in improving the energy efficiency of the battery as well as preventing the battery from overcharge /over-discharge.In response to the country's new energy vehicle development policy,Chinese college students Formula(Formula SAE,FSAE)pure electric car raceemerges in this context.Because of harsh race condition and strict rules,safety and reliability of high degree are badly needed.Against this background,SOC estimation of the car battery is particularly important.In this thesis,18650 model lithium iron phosphate battery of 2000mA(hereafter refer to as Fe battery)provided by Ankao Energy Ltd.Company being used as the subject,introduces the working principles and parameters of the Fe battery,and analyzes the characteristics of its open circuit voltage.Then,Thevenin model is established and the parameters of the model are identified by the method of exponential fitting.The model simulation test was carried out with MATLAB/Simulink by applying pulse current and user-defined current.The simulation results fit the experimental data quite well,which verifies the accuracy of the battery model and parameters identification.On the basis of traditional analysis of estimation methods of State of Charge(SOC),the extended Kalman filter(EKF)algorithm is used as the SOC estimation method in thispaper's.Due to the SOC estimation value of the battery which is obtained by using the Kalman filter can only converge to the current model,high accuracy of the model is required.The estimation of SOC here is performed on the basis of the combination of Ah-EKF and battery model,selected variate and equation and the recursive algorithm.The simulation of EKF algorithm and Ah-EKF algorithm was carried out with MATLAB/Simulink.Compared to the experimental data,the simulation results show that the estimation error of Ah-EKF algorithm is less than 4% and the Ah-EKF algorithm has better estimation accuracy.Lithium-ion battery simulationmodels and the whole vehicle model of FSAE werebuiltbasedonADVISOR.BychoosingdrivingconditionsCYC_IM240,CYC_HWFETand CYC_CUMMUTERto simulate,curve of SOC,current and temperature of battery pack were obtained.Compared with realtest results of FSAE it shows that the models are reasonable to some extent.