Study On Passive Full Equalization Method Of Battery Management System

Lithium batteries have been widely used in new energy and energy storage industries due to their high energy density,low self-discharge rate,and long cycle life.Single lithium batteries have low voltage and small capacity.In order to meet the requirements of voltage level and available capacity in engineering applications,multiple single lithium batteries are usually connected in series and parallel to form a battery pack.The inconsistency between the cells in the pack results in a battery pack whose service life is usually much lower than that of a single cell,and as the frequency of use increases,this inconsistency is magnified,resulting in a rapid decline in the available capacity of the battery pack.This paper studies this issue.First of all,through the analysis of the current main balancing technology,the battery terminal pressure is selected as the reference basis for battery consistency.However,it is difficult for the practical application of balancing technology to achieve consistent battery terminal pressure.In order to solve this problem,this paper proposes a passive full-balance technology that matches the charging and dissipation currents to keep the terminal voltage of the single battery consistent.The on-off time ratio of the built-in switch of the battery management system is adjusted by reading the balance status signal of the single cell,and the average value of the charging current is controlled,so as to match the charging current and the dissipation current,and finally ensure that each cell is fully charged at the end of charging.The terminal pressure of the battery is the same.The terminal pressure of the battery is not amplified with the increase of the cycle frequency,and the terminal pressure tolerance of the single battery can be kept within a small range by only performing a complete charging process,so as to achieve the same terminal pressure.And through simulation experiments,the feasibility of the proposed equalization scheme is verified.Secondly,on the basis of the proposed passive full-balance technology scheme,a low-cost,small-volume battery management system experimental prototype is designed based on the TMS320F28027 chip.In terms of hardware circuit,the main control circuit,power supply circuit,data acquisition circuit,equalization circuit and charge and discharge control circuit are designed and selected.In terms of system software program design,the functional programs such as battery pack SOC estimation,data acquisition,charge and discharge control are analyzed and designed to form a complete battery management system design scheme.Finally,according to the software and hardware scheme designed by the battery management system,a set of BMS for managing 23 strings of lithium iron phosphate battery packs is produced.After multiple charging equalization,the terminal voltage difference of 23 single cells is less than 30 m V,which verifies the effectiveness of passive full equalization technology.