A New Cell Balancing Architecture for Li-ion Battery Packs Based on Cell Redundancy

Li-ion batteries are promoting the development of more and more performing electric vehicles (EVs) and hybrid EVs (HEVs). Thanks to their high energy density and increased current capabilities - which permit to use a relative light and space saving battery pack- these batteries are replacing almost all older battery chemistries in vehicle applications. Despite the advantages these cells provide, before use them in a new design, several drawbacks about safety aspects have to be considered. In fact, Li-ion battery packs require, more than other chemistry base packs, special control systems to maintain the operative conditions in a safe area and to guarantee the best performances in terms of efficiency and pack life time. One of the most challenging problems that have to be tackled by the mentioned control system is the voltage unbalance. This problem arises when more cells are connected in series with the purpose to increase the battery pack voltage. In this paper a new cell balancing architecture based on cell redundancy is proposed. This solution is especially suited to be implemented in vehicle battery management system (BMS) where cost and space reduction are the main requirements.