Reerarch On Power Battery Management System Based On Redundant Unit

Lithium-ion battery has been the ideal power source for electric vehicles because of its merits such as high specific capacity,long cycle life,no memory effect,fast charging,small self-discharge rate and high safety.However,there is a serious problem of inconsistency in the practical use when lithium-ion battery cells are conneted cast in creased reduction of battery state of charge(SOC)than single cells.In order to solve this problem,this paper studies the redundant-unit-based battery management system,which can be real-time monitoring of single cell voltage,temperature,SOC and other parameters.When a particular battery cell is fully charged,it will be cut out of the circuit system-automatically and the charging voltage will be adjusted accordingly in the charging process,which will not be ended up until the entire batteries are finished full-charge.On the other hand,those batteries of higher power will be firstly selected to discharge system-automatically in the discharging process,which will not be ended up until all the redundant battery power is discharged to zero.What’s more,when battrry fails,the specific battery cell can be automatically bypassed from the circuit to avoid the potential safety hazards,and thus the overall reliability of the battery pack.The main contents of this paper are as follows:Firstly,the overall structure of the battery management system is designed with STC12C5A32S2 of single-chip 51 as the MCU of battery management system.Then the author has designed the voltage,current and temperature detection circuit.The thermal management control scheme has been studied.The test program and monitoring interface of the battery have been written with Visual Basic.Secondly,the author studies the influence that the Coulomb efficiency,temperature effect and cycle life of lithium iron phosphate battery exert on its capacity,and the corresponding function relation is obtained.On this basis,MATLAB/Simulink are adopted for the SOC estimation model with modified ampere-hour integration approach,the simulation analysis of which is also conducted compared with that of its traditional one under a constant small current,a sinusoidal current and a low temperature condition.The simulation results show that the SOC is closer to the real value when estimated through modified ampere-hour integration approach.Thirdly,based on the research of existing equalization control system,an equalization control system based on redundant unit is proposed.The author also studies and designs the hardware structure,software module and equalization control strategy,whose feasibility is verified by the balanced charge experiment.Finally,this paper studies the discharge switching strategy of the battery pack.Together with numerical simulation approach,the discharge program written with Visual Basic software is used to study the effects that the number of redundancy,the discharge time interval and the standard deviation of the initial capacity distribution have on the discharge efficiency.The results show that the higher the number of redundancy,the shorter the discharge switching time,and the smaller the initial standard deviation,the higher the discharge efficiency.Finally,the simulation results are verified by experiments.In this paper,the battery management system based on the redundant unit is studied attempting to analyze and solve the problem of capacity drop and security caused by the battery inconsistency,which has certain theoretical and guiding significance for improving the capacity utilization and increasing the safety of the battery pack in practical use.