Lithium Battery Pack Management System Design And Active Equalization Technology Research

With the increasing global energy crisis,in order to enhance my country’s competitiveness in the world energy market and reduce the negative impact of the instability of the international situation,the vigorous development of the new energy automobile industry has been raised to the height of the national strategy.Lithium-ion batteries(hereinafter referred to as lithium batteries)are widely used in new energy electric vehicles due to their high energy density,light weight,and low self-discharge rate.In the actual use of lithium batteries,multiple single lithium batteries are usually connected in series and parallel into groups to meet the application requirements of different capacities and different voltage levels.However,due to the inconsistency between the individual cells,on the one hand,the overall usable capacity of the battery pack is reduced,and on the other hand,there are hidden safety hazards;therefore,it is necessary to design a reliable battery management system to ensure safe,efficient and long-life operation of lithium batteries.Starting from the battery information collection technology of the battery management system,the current methods of voltage collection,current collection,and temperature collection are analyzed and compared,and the advantages and disadvantages of the existing sampling methods are summarized;then the balanced topology and balanced variables are detailed in combination with actual engineering applications.Description,and then introduced other issues in the battery management system.This article analyzes the causes of lithium battery inconsistency in detail and discusses the improvement measures for inconsistency;for the selection of equilibrium variables,through comparative analysis of the advantages and disadvantages and feasibility of commonly used equilibrium variables,appropriate equilibrium variables and state of charge are selected.(State of Charge,SOC)estimation method.At the same time,through charging and discharging test experiments,the functional relationship between SOC and Open Circuit Voltage(OCV)is obtained,which is a good foundation for the subsequent formulation of equilibrium strategies.Based on the actual engineering problem,the overall plan of the balance management system is designed.Aiming at the problem of the high price of the voltage sampling chip,based on the switch array P2 C type balance architecture,it is proposed to use the switch in turn to gate the voltage of each single cell of the lithium battery pack.This method realizes the multiplexing of voltage sampling and equalization functions.With only one AD port,all battery voltages of the battery pack can be collected,avoiding the use of voltage sampling chips and greatly reducing the equalization cost.At the same time,the flyback converter is selected as the equalization main circuit of the equalization management system,its working mode is analyzed in detail,and the corresponding parameters of the equalization main circuit are designed in combination with the equalization scheme,and the correctness of the theoretical analysis is verified by Saber simulation.Aiming at the long balance time each time,the switch should be normally open and normally closed,and the MOS transistor drive needs to be isolated and floating,a normally open and normally closed isolated drive circuit is designed.Taking into account the large number of switches and the need for a PWM signal to be turned on,combined with the feature that each switch does not need to be turned on at the same time for each strobe,a switch gating circuit is designed.This circuit only uses one PWM,6 I/O ports can realize the gating of 14 lithium batteries.Then combined with the balanced architecture,analyzed its balanced ideas,and proposed a fast constant current balancing strategy based on the switch array P2 C balanced architecture.The balancing strategy has the advantages of low cost,high speed,high precision,simple control,and fewer switch gating times,etc.advantage.Finally,a balanced management experiment platform was built,and the functions of each module of the balanced management system were tested.The balance test of 14 lithium batteries verified the feasibility and practicability of the proposed balancing strategy.