Research And Design Of Active Equilibrium System For Lithium-ion Battery Of Electric Vehicle

In recent years,the state has now vigorously developed pure electric vehicles,and the power battery group is the energy source of the electric vehicle,the management of the battery pack is particularly important.A good battery management system can improve the battery power and life expectancy.In this paper,the ternary polymer lithium pouch battery is taken as the research object,and the active equalization technology of the battery management system is deeply studied.A double balanced extension structure based on the SOC(State Of Charge)consistency as the equilibrium index,based on the transformation of the traditional resonant converter,is proposed,and then complete the design of battery management system based on the equalization circuit.The main work of this article is as follows:Firstly,summarize the advantages and disadvantages of the existing battery equivalent model,and then combine the actual operating conditions of the pure electric vehicle,finally found the equivalent circuit modelPNGV model suitable for this article,In order to increase the guiding significance of the equivalent model to the practical use in the later period,the PNGV model is improved.After that,the parameters of the improved model were identified by using the HPPC experimental data of the battery,and the built-up battery model was verified by constant current pulse discharge.Then the existing equalization methods of battery pack are summarized,and the advantages and disadvantages of each circuit are analyzed from the aspects of balance efficiency,control difficulty and so on.Finally,an energy non-dissipative type circuit based on resonant converters is selected.The energy loss of the circuit equalization process is small,but the efficiency is low.Therefore,the equalization circuit has been modified.and the original single-layer structure is improved to a double-layer structure to improve the equalization efficiency.In addition,In order to solve the problem of low efficiency in the later period of charge equalization,A diode-assisted equalization module has been added.Then the simulation model is built in MATLAB,and the simulation results show that the circuit can effectively improve the efficiency of equilibrium.Finally,in order to verify the effectiveness of the improved equilibrium structure used,a battery management system based on the abo ve balanced circuit is designed.The hardware and software were designed respectively.The hardware structure was a master-slave structure.The hardware structure is a master-slave structure.The main chip adopts Freescale’s 16-bit microcontroller MC9SXDP512,and the acquisition chip uses AD7280 A voltage and temperature acquisition and ACS712 current acquisition.After that,based on the CodeWarrior software development environment,the main program and the subprograms are written,designed the Labview as upper computer to display and record battery real-time data.Then,based on the built experimental platform,the charging equalizatio n experiment of the 6-cell batteries is done.The experimental results also show that the battery management system can manage the battery pack well,and effectively improve the balance efficiency.