Research And Development Of Lithium Battery Equalization System Based On Extended Hierarchical Strategy

As one of the key components of electric vehicles,the power battery pack has a significa nt impact on the vehicle dynamic performance,economical efficiency and security.And,it is the core technology of electric vehicles.Due to the inevitab le inconsistency problem among the same type of single cel s,the service life of the power battery pack becomes an main factor restricting the development of the electric vehicle.The equalization of each cell can be realized by designing a equalization management system for power battery pack.Battery equaliza t io n is to realize the energy equalization of each cell in the battery pack,and eliminate the negative effects caused by the inconsistency among single cel s.Battery equalization is composed of the equalization circuit and the corresponding equalization control strategy.In this paper,ternary lithium battery is used as the research object.By analyzing the development tendency of the equalization technology for battery pack,contraposing the working condition and combined model of the power battery pack,the equalization circuit and the equalization control strategy of the power battery pack are studied and developed.According to the combination model of the power battery pack,by analyzing the topology of the commonly used battery equalization circuit,an extensible 2N battery pack equaliza t io n circuit is proposed.Through the quantitative analysis of the working principle and working process of the equalization circuit,the quantitative relationship between the charge and discharge current,the inductance L,the switching period T and the duty ratio D is obtained,and the limiting equation of duty cycle D which can reset the inductor in each period is given.According to the characteristics of lithium battery and equalization circuit,the software design of battery equalization system based on ?C/OS-II embedded system is completed.Two different control strategies,“charge equalization subroutine” and “discharge and shelving equalization subroutine”,are mainly designed to balance the battery pack,so as to realize the organic combination of static equilibrium and dynamic adjustment.Finally,the simulation analysis and experimental verification of the equalization circuit and the equalization control strategy are carried out.Simulation and experimental results show that,regardless of the working state of the battery pack,the equalization circuit and the control strategy can effectively achieve the balance of the battery pack,and the balance current is large.