Research On Parameter Online Identification And SOC Estimation Of Lithium-ion Battery

Lithium-ion batteries have become one of the main energy sources and are commonly used in various small and medium-sized devices.Therefore,the safety of lithium-ion batteries has a major impact on our production and life.The battery management system mainly monitors the battery operating status,and the battery state of charge(SOC,state of charge)is estimated to be one of the main functions of the battery management system.The accuracy of battery state of charge estimation can not only provide timely feedback on the power usage of various electrical equipment,but also contribute to the safety of battery use,which is very important for the study of lithium battery SOC estimation.Whether the battery SOC estimation is accurate or not has a great relationship with whether the battery parameter identification conforms to the internal change law of the battery,so this article mainly focuses on the lithium-ion battery identification method and SOC estimation.Firstly,the background and significance of the subject are introduced,and the current research status of battery estimation models and SOC estimation are discussed.Based on the analysis of the structure and working principle of the lithium battery,experimental research on the characteristics of the lithium battery,mainly including battery voltage characteristics,discharge rate characteristics,capacity characteristics and resistance characteristics,etc.Secondly,based on the second-order RC equivalent circuit model,the offline and online parameter identification methods of lithium batteries are studied,and the validity of the conclusion identification method is verified by using the experimental data of charging and discharging.Among them,the off-line identification method obtains the internal resistance,polarization internal resistance,polarization capacitance and other parameters of the second-order RC model through curve fitting identification based on phased discharge experiments.The online identification adopts the recursive least square identification method with forgetting factor to identify the battery second-order RC model parameters online in real time.Finally,based on the analysis of the classic Kalman filter method(KF)principle,the realization method of lithium-ion battery SOC estimation based on the extended Kalman filter method(EKF)and the unscented Kalman filter method(UKF)is given.And it has been simulated and verified in MATLAB/Simulink environment.The simulation results show that,compared with EKF,when the UKF method is used to estimate the lithium battery SOC,the convergence speed is faster and the error is smaller.