Research On Active Balance Technology Of Power Battery

Lithium-ion batteries,which are the most comprehensive power batteries,are widely used as electric power sources in electric vehicles.However,since the performance indexes of the single-cell battery cannot meet the requirements of the electric vehicle,it is usually required to form a battery pack by serially connecting a plurality of cells to obtain a higher output voltage and output power.However,due to the existing lithium battery manufacturing technology,the performance difference between the individual cells is unavoidable.And as the usage environment changes and the usage time increases,this performance difference will be gradually amplified,eventually affecting the normal use of the battery pack and the normal operation of the electric vehicle.This paper analyzes the various causes of inconsistencies in single cells and summarizes the possible negative effects of this problem.The open circuit voltage of the four Sanyo 18650 lithium batteries and the relationship between the operating voltage and the state of charge(SOC)of the battery were calibrated by experiments.A simple SOC estimation method is studied.Based on this analysis,the advantages,disadvantages and possibilities of SOC,open circuit voltage and working voltage as equalization variables are compared.In order to make full use of battery energy and improve equalization efficiency,this paper designs a bidirectional flyback converter based on active clamp technology as the main circuit of the equalization system.The topology is suitable for centralized active equalization technology,which can achieve bidirectional flow of energy between any single cell and the entire battery.Firstly,the working principle of this topology is analyzed in detail,and the possibility of implementing soft switching is demonstrated.Then the main parameters of the converter are designed.Finally,the correctness and feasibility of theoretical analysis and parameter design are verified by Matlab simulation.A complete active equalization system is designed,including the main signal acquisition circuit and a switch array for centralized active equalization.Then a clear equilibrium process and strategy is developed to help the entire system increase the speed and efficiency of active balancing.On the basis of all software and hardware design,build a complete equalization system prototype,develop a balanced strategy,and use four Sanyo 18650 series battery packs as test objects to carry out related equilibrium experiments to evaluate the equilibrium effect of the equalization system and prove its improvement of body battery inconsistency.