Switched-capacitor equalizers using hybrid balancing paths for series-connected energy storage cells

Due to the high voltage stress on switch, series parallel switched-capacitor (SPSC) equalizers have a low reliability. To reduce the voltage stress on switch, two switched-capacitor (SC) equalizers using hybrid balancing paths are proposed in this paper. In the proposed SC equalizers, balancing paths among cells are used to implement the energy transfer from any cell to any cell (AC2AC), and balancing paths among substrings are used to improve balancing speed among cells. The proposed SC equalizers are decomposed into multiple SC balancing units and three graph networks to simplify the performance analysis of the equalizer. Based on the graph networks of the equalizer, the average length of balancing paths among cells is used to mathematically analyze the balancing speed among cells. A modularized method is proposed for the high voltage applications, where no additional switches are needed and the voltage stress on switch decreases further. The modularized method implements the trade-off between the balancing speed among modules and the balancing current stress of cell. Simulation and experimental results are provided to verify the validity of the proposed equalizers.