Research On SOC Estimation And Equilibrium Management Technology For Lithium Ion Power Battery

In recent years,the problem of worldwide environmental pollution and oil depletion has become prominent increasingly.With the problems of Global warming,frequent smog and terrible air quality appeared,people's health will be threatened and quality of life can not be guaranteed.In order to improve the above problems,in response to the national concept of green,coordinated and sustainable development,the research and development of environment-friendly new energy electric vehicles has become the focus of future development.At present,lithium-ion power batteries,as the main source of power for new energy electric vehicles,have attracted increasing attention.Considering the inconsistencies and non-linear structural characteristics of their single cells,they are improving the accuracy of SOC estimation and improving battery imbalance.This aspect has brought greater difficulties to scientific research.Therefore,this paper focuses on the research of SOC estimation and the strategy of lithium-ion battery equalization.The specific work is as follows:(1)Equivalent circuit model construction.Based on the analysis of the internal characteristics of lithium-ion battery,according to its nonlinear characteristics,combined with the steady-state characteristics and transient characteristics of lithium battery,a second-order RC equivalent circuit model is established.The SOC-OCV function curve is fitted by experimental,using MATLAB fitting tools.Under HPPC pulse discharge conditions,the parameters of the model are identified and verified.(2)Estimation of battery state of charge SOC.Considering the effect of the actual high and low temperature conditions on the ohmic internal resistance of the battery,the ohmic resistance exhibits a large sensitivity at a low temperature state and a gentle performance at a high temperature state.Therefore,the deviation control error is added to the observation equation.The SOC value estimation is completed by the improved extended Kalman filter EKF algorithm and the particle filter PF algorithm using residual resampling for weight redistribution respectively.The results show that the absolute error of the EKF algorithm is within 3.12%,and the absolute error of the PF algorithm is within 2.81%.Both algorithms improve the estimation accuracy of SOC to a certain extent,and the estimation accuracy of PF algorithm is better,so as to provide the basis for balancing control variables for battery pack equalization.(3)Research on active equalization strategy of lithium ion power battery pack.A two-layer active equalization circuit with SOC as the equalization control variable and based on power inductor and supporting energy bidirectional transmission is proposed.A two-level equalization strategy was developed to equalize the SOC between any adjacent two cells,and a circuit model was built in MATLAB/Simulink for simulation equalization.The results show that under this strategy,the battery pack equalization effect is obvious.At the end of the thesis,the full text is summarized,and the future work is prospected.