A Study On SOC Estimation Of Power Battery Based On Linear Parameter Varying Kalman Filter

Power battery is the energy source of electric car.Not only is the SOC estimation one of the most important functions in battery management system,but also the SOC value is an important parameter of vehicle performance.Accurate SOC estimation of power battery could improve battery performance and reduce maintenance costs.Meanwhile,it may provide accurate basis for the energy distribution and protection for the drivers to drive safely.Lithium iron phosphate(LiFePO4) battery is studied in this paper.The study is carried out from the aspects of battery performance tests,equivalent circuit model,SOC estimation methods,etc.The main work of this paper are as follows:⑴ The charging and discharging characteristics,open circuit voltage characteristic,resistance characteristic,efficiency characteristic and hysteresis voltage characteristic of lithiumion battery are studied based on the working principles and numerous test.Considering the influence from coulomb efficiency, temperature and the self-discharge, correction factor is presented to amend the definition formula of SOC.⑵ A second-order RC circuit model combined with hysteresis voltage is established and the battery model parameters are gained using least square method and identification tests designed.The maximum error between test value and simulation value accounts for 0.47% of nominal voltage and meet the test requirement.The result shows that the model has a good precision.⑶ LPV-Kalman filter is designed to estimate SOC of battery based on KF and LPV theory.Hybrid vehicle model and battery SOC estimation model are established in software MATLAB Simulink.The result of simulation under NEDC condition shows that the SOC varies from 0.95 to 0.35 and conforms to the setting of control strategy.The feasibility and effectiveness of SOC estimation which presented in this paper are verified.