Research On Series Equalization Control Strategy Of Power Battery Pack

Under the guidance of national policies and the promotion of market situation,the new energy electric vehicle industry has experienced a stage of rapid development.After a cycle of use,a large number of power batteries ushered in the peak of retirement.Although decommissioned power batteries cannot be used in electric vehicles,they can be used in domains such as energy storage where battery performance is not highly required.When reusing the battery,the most important thing is to ensure that the State of Charge(SOC)of the single battery in the battery pack is consistent,so it is necessary to control the balance of the battery pack.Due to the large number of single cells in series battery pack,the energy transfer efficiency of simple equalization method is low,so the modular equalization control strategy is adopted.(1)For the SOC estimation method of lithium battery,the Least Square Support Vector Machine(LSSVM)is adopted as the prediction model,and the Estimation of Distribution Algorithm(EDA)is proposed to optimize the width of the radial basis kernel and regularization parameters of LSSVM,which makes the prediction model have higher accuracy.(2)Aiming at the inductance equalization circuit of the underlying module,a layered and piecewise equalization control strategy is proposed,which uses SOC consistency as the goal of equalization.The equalization circuit is divided into three levels.The difference between the SOC of battery B4 and the average value of battery pack is taken as the equalization opening condition.When the difference is less than or equal to ?,the first and second level circuits are equalized at the same time,and the third level circuit is equalized after completion.When the difference is larger than ?,the three-level circuit is equalized according to the SOC difference as the opening condition.(3)As for the two-way fly-back convertor equilibrium circuit of the top module,the consistency of SOC is also taken as the equilibrium goal.The difference between the average SOC of the bottom module and the average SOC of all the single battery is taken as the opening condition,so as to determine the flow direction of energy.For the overall equalization control,a piecewise equalization control strategy is proposed.The range of the single battery in each bottom module is taken as the opening condition.If the range is less than or equal to ?,the bottom and the top layer are equalized simultaneously.If the range is larger than ?,the bottom module is balanced first,and then the top module is balanced to achieve time-sharing equilibrium.(4)In the MATLAB environment,the ADVISOR software is used to extract the data of current,voltage,temperature and SOC,and the obtained data are used to verify the effectiveness of the proposed EDA-LSSVM method to estimate the battery SOC.A simulation model is built to simulate the bottom level and the overall equalization control strategy respectively.Compared with other strategies,the proposed equalization strategy in this paper has the highest energy transfer efficiency and a faster equalization speed,which verifies the feasibility of the bottom level and the overall piecewise equalization control strategy.