Research On SOC Estimation Method Of Lithium Ion Battery

With the development of economy and technology,energy and environmental problems are increasingly severe,and electric energy is a clean secondary energy with the unique advantage of using renewable energy to generate electricity.As an important carrier of electric energy,batteries play a decisive role in production and life.Accurate estimation techniques of State of Charge(SOC)of batteries have always been the focus of research in academia.SOC estimation should be provided high accuracy information.Firstly,this thesis analyzed the working principle of lithium-ion batteries,and battery performance testing equipment is selected to perform different performance testing experiments for specific lithium ion batteries,and several characteristics,such as the open-circuit voltage characteristics,capacity characteristics,charge and discharge characteristics,temperature characteristics,and the effect of the number of charging cycles on the battery capacity of the battery,are tested and analyzed,laying the foundation for the whole battery research.Secondly,to improve the accuracy of SOC estimation,the methods to improve accuracy of battery equivalent circuit model.After analyzing a variety of models,the PNGV(Partnership for a New Generation of Vehicles)equivalent circuit model of battery was selected at last.Open-circuit voltage and state of charge(OCV-SOC)curves was obtained through experiments.At the same time,the polarization characteristics of the battery were analyzed through HPPC(Hybrid Pulse Power Characterization)pulse experiments.After fitting the experimental data,the parameters of the battery equivalent circuit model were identified,and the 0.1C constant current discharge simulation was implemented in MATLAB.Simulation results prove that the improved model can truly reflect the internal working state of the battery.Due to the non-linear characteristics of the battery,after analyzing the commonly used SOC estimation methods at home and abroad,the extended Kalman filter(EKF)algorithm,with better adaptability to nonlinear systems,is picked out finally.Based on Kalman filter algorithm SOC estimation,EKF algorithm is used to estimate the ohmic resistance of the battery to optimize the battery equivalent state space model,thus forming a new Kalman filter estimation algorithm(NEKF).Through the simulation in MATLAB under the constant current and US Urban Cycle Conditions(UDDS)conditions,the effectiveness of improved method to improve the estimation accuracy is validated.