Reasearch On Active Equalization Technology Of Battery Pack Based On Symmetrical Switch Array

In recent years,with national guidance and market promotion,power batteries have been widely used in the field of new energy vehicles,but because the batteries are easily affected by the manufacturing process and working environment,resulting in the unbalanced state of charge between batteries and other conditions,which reduces the energy utilization and available capacity of the battery pack and seriously affects the cycle life of the battery pack.The purpose of this paper is to improve the inconsistency problem among batteries and propose a research scheme of active battery pack equalization system based on symmetrical switch array.Firstly,the main equalization units are studied in the equalization system.The equalization units can be used in different bidirectional DC-DC converters,and the topologies of three of them,the bidirectional flyback converter,the bidirectional forward converter and the dual active full-bridge circuit(DAB),are analyzed and compared in this paper.After that,the control methods of the bidirectional flyback converter,including voltage closed-loop control and current closed-loop control,are analyzed.The operating principle of RCD absorption circuit is analyzed for the problem of high frequency transformer leakage and partial excitation energy renewal in flyback converters.The transmitted power analysis and current stress analysis are performed for the dual active full-bridge circuit.Finally,a simulation model is built in MATLAB/Simulink to simulate the basic operating principles and control strategies of the bidirectional forward converter and flyback converter.Secondly,the battery pack equalization system is introduced,and the structure of active equalization system based on symmetrical switch array is proposed,and analyzed and compared with the equalization system of single-switch array and modular equalization system.The single-switch array equalization system has a single power direction;the modular equalization system is relatively complicated to control;while for the symmetrical switch array equalization system,the power of its whole circuit is bidirectional,the control strategy is more flexible and the equalization speed is faster.Finally,the working principle and structure of the equalization system are analyzed respectively.Again,the voltage-based equalization control strategy,the SOC-based equalization control strategy and the symmetric switch array-based equalization control strategy are introduced to address the inconsistency problem among cells.In order to verify the effectiveness and feasibility of the equalization control strategy,a simulation platform is built to verify and analyze it.Finally,the hardware and software design of the battery pack equalization system is carried out,and the experimental platform of the equalization system is built to verify the equalization control strategy and the equalization effect of the single switch array equalization system and the symmetric switch array equalization system,which can realize the equalization control among the battery modules.