The Management System And Balancing Strategy Of Lithium-ion Batteries

Power batteries is the key part of electrical vehicles.Batteries are connected in series to provide sufficient power for electrical vehicles and energy storage systems for one single battery has limited capacity and voltage.BMS is needed for series-connected batteries to achieve the fuctions of condition monitoring 、 safety management and balancing control.Imbalance of battery cells siginificantly reduces capacity usage ratio、lifetime and safety of the battery pack.Battery balancing techniques are used to solve imbalance problem.A Holonomic balancing system is comprised of battery management system、balancing circuits and balancing strategy.This paper mainly focuses on the balancing strategy and the management system designing of battery pack.Traditional balancing strategies aim at redistributing charge between batteries with more energy and those with less energy through balancing circuits to achieve balance,conducted after imbalance has emerged and achieved a certain degree.To maintain a fast balancing performance,large balancing current is required.Accordingly,the voltage and current stress of circuit devices are improved,which increases the cost and more heat will be generated in a unit time.This paper proposes a balancing strategy based on the change rate of SOC,which is conducted during the charging process of the battery pack.The proposed balancing strategy can restrain imbalance from emerging and expanding with the benefits of small balancing current.A two-battery balancing experiment and seven-battery balancing experiment were conducted respectively to verify the proposed balancing strategy.There is more and more demanding on function safety of BMS along with the development of electrical vehicles.This paper fitstly designed a master-slave BMS based on LTC6803 acquisition chip,to meet the requirements of function safety,A chrysanthemum chain BMS scheme based on MC33771 chip(ASIL-C)and MPC5744 P chip(ASIL-D)was developed.This is a system security level to achieve ASIL-D BMS design scheme.The hardware platforms of the two BMS schemes based on LTC6803 and MC33771 were built respectively,and the related program languages were written and debugged.BMS were connected to batteries to verify the functions.