Research On State Of Charge Estimation And Equalization Technique Of Lithium-Ion Battery

Faced with the depletion of fossil energy shortages and the increasingly serious environmental pollution problems caused by the use of fossil energy,green travel and low-carbon transportation have become the development direction of the social and transportation industries.Nowadays,with the continuous advancement of science and technology,the automotive industry is developing towards electrification,intelligence,networking and light weight.The rise of electric vehicles is precisely adapted to this development trend and technology direction.The development of new energy vehicles will bring extremely favorable opportunities for China to seize the commanding heights and voice in the global automotive industry.The energy of electric vehicles mainly comes from vehicle power batteries,so battery management system is an extremely important part of electric vehicles.The main functions of battery management system include battery state of charge(SOC)estimation,balance management,battery pack thermal management and so on.The battery management system can realize the safe and effective operation of the battery pack,prolong the service life of the battery pack,and improve the utilization efficiency of the battery pack energy.This dissertation selects the SOC estimation and balance management in the battery management system as the research direction and conducts research on the subject.In this dissertation,the ternary lithium-ion battery is taken as the research object,and the Thevenin equivalent circuit model with temperature compensation is established.In the wide temperature range(0~40°C),the capacity test,open circuit voltage test,hybrid pulse power characterization and other tests were carried out with an interval of 10°C.The battery parameters were calculated by the recursive least squares method with forgetting factor.This dissertation establishes the three-dimensional relationship among battery parameters,temperature and SOC,and fully depicts the variation of internal parameters of the battery with temperature.In MATLAB/Simulink,a battery model was built to verify the effectiveness of the established battery model.Secondly,the unscented Kalman filter algorithm is introduced in detail.In this dissertation,based on the established Thevenin equivalent circuit model,an unscented Kalman filter algorithm based on temperature compensation is proposed to estimate the SOC of ternary battery.In this dissertation,the effectiveness of the proposed algorithm is verified by the new European driving circle.Experiments and simulations show that compared with the traditional unscented Kalman filter algorithm in different ambient temperatures,the effectiveness and robustness of the proposed algorithm are verified.Finally,an active equalization circuit topology that can achieve simultaneous equalization between different layers is proposed.Combined with the designed hierarchical equalization strategy,the problem of battery voltage inconsistency in the power battery pack can be quickly solved.The feasibility of the proposed topology and equalization strategy is verified by simulation and experiment.