A comprehensive overview of the dc-dc converter-based battery charge balancing methods in electric vehicles

With the development of electric vehicle (EV) technologies, efficient and reliable use of rechargeable batteries (RBs) has become the key subject for automotive manufacturers. Among RBs, lithium-ion battery technology is the most prominent about high specific energy and specific power. The lithium-ion battery pack consists of battery cells with low terminal voltage connected in series to meet the voltage requirement of the EV system. However, the useable capacity of the battery pack is restricted by the low charge cell among the string. The manufacturing inconsistency and different operating conditions of each cell cause the charge imbalances in the battery pack. These imbalances lead to the reduction of the useable capacity, acceleration of cell degradation, and, more importantly, serious safety hazards like overcharging. In all EVs and hybrid electric vehicles (HEVs) using lithium-ion battery systems, the cell balancing controller is an essential task which managed by the battery management system (BMS) to improve battery life cycle and safety. This paper presents a comprehensive overview of the DC-DC converter-based battery balancing system because of the impactful contribution to the charge balancing control and the design of balancing control algorithms. Moreover, other BMS functions such as state of charge (SOC) estimation, which affects balancing performance, are handled in this review.