Active Cell Equalizer Based on Coupled-Inductor Cuk Converter for Improved Cell Balancing Speed

Lithium-ion battery cells connected in series generally have state of charge imbalance, which shortens lifetime of battery systems. Therefore, many researches have been conducted to balance the battery cells. However, conventional circuits have low balancing speed and low power efficiency. To solve the problems, cell equalizer using coupled-inductor Cuk converters is proposed in this paper. The proposed circuit not only has multi-winding transformers, but also Cuk converter structure, which makes a large balancing current. In addition, the proposed circuit has low voltage stress of switches and small freewheeling currents, which makes higher efficiency. As a result, the proposed circuit has high balancing speed and efficiency. The effectiveness of the proposed circuit was verified by experiments.