A Power Conversion Technique with Hierarchical Equalization Charging Topology for LiFePO₄ Batteries

An energy-storage scheme with hierarchical equalization charging topology applied in a series-connected battery system is proposed in this paper. The proposed hierarchical equalization charging topology (HECT), which combines an equalizer-within module (EWM) and an equalizer between the modules (EBM), is able to rapidly achieve charging balance among a large number of cells in battery modules. The EWM is composed of a buck-boost converter, while a flyback converter constitutes the EBM. Besides, the voltage of each cell in battery modules can be accurately monitored by utilizing the proposed HECT control architecture. In addition, fewer circuit elements are required in the proposed battery equalization system and a faster balancing speed can be achieved. Satisfactory experimental results were obtained by using 12 LiFePO₄ batteries, and the performance was improved by about 50% in reducing the battery voltage deviation realized in the proposed battery balancing system, which verified the function of the proposed HECT scheme.