Design And Research Of Pure Electric Vehicle Battery Equalization Management System

Along with the development of new energy and environmental protection attracting more and more people's attention,pure electric vehicles gradually become a very important part of the sustainable development of the auto industry because of the advantages of its feature of zero emissions and high energy utilization rate.As the only power supply of pure electric vehicle,the performance and capacity utilization rate of power battery pack are far lower than the battery monomer because there is inconsistency between the battery monomer in the group,and due to the complexity of pure electric vehicles' working environment and running condition,it makes the power battery pack's inconsistency in the practical working may be increasing,all of these have seriously restricted on the development and promotion of pure electric vehicles.This paper based on analyzing and studying the reasons for the formation of inconsistencies,put lithium iron phosphate power battery as the research object,and designed the corresponding equalization circuit structure and control strategy to simulation validation,came true the system hardware and software,finally carried on the bench test to verify.The main content of this paper is as follows:(1)The cause of the formation of the inconsistencies of power battery packwas parsed from the three aspects such as manufacture,work and store.Then this paper analyzed and summarized the existing solution measures that can improve the consistency of the power battery pack,and illustrated parameters'(power battery voltage,resistance and SOC)form of the behavior in performance aspect.Next the thesis studied and analyzed the advantages and disadvantages when put open circuit voltage,the working voltage or SOC as balanced variable.Ultimately this thesis determined the working voltage as balanced variable for power battery equilibrium under different state.(2)The characteristics of existing kinds of different balanced circuit structures were compared and studied.Then the paper selected active equalization circuit structure based on fly-back transformer and calculated relevant parameters of this circuit structure(3)This thesis developed two equilibrium control strategies(charging equalization and discharging equalization)according to the selected circuit structure: 1)when the maximum voltage value of power battery monomer reached charging cut-off voltage,equilibrium control system immediately would stopped charging to balance at this time,power battery pack recharged when battery voltage was less than the set threshold.Repeating the process until the voltage of each monomer battery achieving consistently or equalizing charging number reaching the set value;2)when the minimum voltage value of power battery monomer reached discharging cut-off voltage,equilibrium control system immediately would start to balance at this time,power battery packstopped the equilibrium when battery voltage was less than the set threshold or equalizing discharging number reaching the set value.Repeating the process until the voltage of each monomer battery achieving consistently or equalizing charge number reaching the set value.(4)This paper selected the distributed structure as equilibrium system overall architecture.Then the thesis respectively designed the power supply module,voltage sampling module,current sampling module,balanced module and communication module of hardware circuit and developed corresponding software.Next equalization charging and discharging test benches were constructed to do charging and discharging experiments.Finally the paper verified that the designed balanced control system did improve the consistency and available capacity of power battery pack.