Center-Cell Concentration Structure of a Cell-to-Cell Balancing Circuit With a Reduced Number of Switches

Among the various cell balancing circuits for series-connected batteries, the bidirectional cell-to-cell balancing structure using two switches per cell shows good balancing ability. However, an increase in the number of switches leads to an increase in both cost and size. To reduce the number of switches, this paper proposes a new cell-to-cell balancing circuit with a center-cell concentration structure. The proposed circuit collects the charges of an overcharged cell into the center cell, and then the collected charges are redistributed to the other cells. The proposed circuit has a unidirectional balancing structure with single switch per cell. However, it can achieve competitive balancing ability when compared with the bidirectional structure. In this paper, the operational principles of the proposed circuit are analyzed, and a comparison between the conventional and proposed circuits is shown. To verify the validity of the proposed circuit, experiments with 15.5-Ah batteries are carried out, and the experimental results demonstrate the improved cell balancing ability although a single switch is used per cell.