Design and Analysis of a Half-Bridge Converter-Based Hierarchical Battery Equalizer

In this manuscript, a half-bridge converter-based hierarchical battery equalizer is proposed and analyzed. On the low-voltage side of this equalizer, two adjacent battery cells and corresponding switches and transformer windings form a half-bridge unit, and the cells in this unit can be equalized by means of the magnetizing inductance of the transformer. Further, the secondary sides of these transformers are linked to a high-voltage half-bridge unit, whose output connects the entire battery string to realize the equalization between the low-voltage half-bridge units. The proposed scheme achieves time-division multiplexing of power devices in the equalization process, which effectively reduces the cost and volume of the equalizer, and improves its modularity and practicality. Besides, the two-stage balancing structure and continuously controllable equalization current ensure the equalization speed and equalization efficiency. The operating state and principle, parameter calculation and control strategy of the equalizer are thoroughly analyzed. Finally, the equalization verification results based on four series-connected battery cells fully validate the feasibility and correctness of the proposed two-stage hierarchical battery equalizer.