Research On SOC Observation Method Of Li-Ion Batteries Based On Model With Variable Parameters

With high energy density,long life period and low self-discharge rate,the lithium ion battery is known as one of the fastest growing and promising large scale energy storage battery in the field of power generation.However,the core problems such as safety,performance and the lifetime of the battery have not been fundamentally solved.As one of the core technologies of battery management system?BMS?,the observation technology of the battery state of charge?SOC?plays an indispensable role in maintaining the safety and high efficiency of the battery system and prolonging the battery's life period etc..In this thesis,the research on the real-time observation method of SOC of the Li-ion battery is carried on aiming at the current problems of the low precision of the battery models and the SOC observation results,and the TS-EKF union estimator based on 2^nd-order RC model with variable parameters is finally designed.In order to realize the accurate modeling of the Li-ion battery,firstly some basic experimental tests are carried out on the target Li-ion battery,the test data is analyzed to obtain the performance characteristics and response laws of the Li-ion battery;Secondly,based on the conclusion of these basic tests and the commonly used and improved equivalent circuit model,the 2^nd-order RC model with variable parameters is built to adapt to complicated and changeable working conditions;Thirdly,The functional relationship between electromotive force and SOC of the Li-ion battery,and the relationship between ohmic resistance and temperature of the battery are calibrated respectively,and the parameters of the polarization processes are obtained by the hybrid pulse power characteristics?HPPC?test;then,the same inputs are applied to the actual Li-ion battery and the model,and then the model is proved to be accurate by comparison of the two output responses.Based on the battery model above,an accurate and efficient SOC observation method is designed for Li-ion battery.Firstly,the AH integral estimator is built according to the definition of SOC,and then the EKF estimator is established by introducing the Extended Kalman Filter principle;Then,combined with the T-S fuzzy principle,the TS-EKF union estimator is eventually designed.Finally,the accuracy and the practicability of the SOC observation method with the core technologies are verified based on the simulation platform of Simulink and the practical platform of Raspberry Pi respectively.Then compared with the existing BQ27546-G1 estimator,the accuracy and practicability of the TS-EKF joint estimator are proved to be better.The research ideas and results in this thesis can be used as reference to the multi-state joint estimation of the Li-ion battery for a deeper level.Meanwhile,an effective theoretical basis and an exploration direction are provided for the research and development of the BMS.