Double-switch single-inductor resonant cell equalizer using voltage multiplier for series-connected supercapacitors

Cell equalizers are usually used for series-connected energy storage cells, such as lithium-ion cells and supercapacitors (SCs), to eliminate voltage imbalance that may cause premature deterioration and reduce the available energies of the cells. Because conventional cell equalizers are based on multiple individual bidirectional dc-dc converters, the number of switches, inductors, and transformers increases proportionally with the number of series-connected energy storage cells. As compared to conventional equalizers, a double-switch resonant cell equalizer using a voltage multiplier, which is proposed in this paper, can reduce the circuit complexity significantly because of its double-switch single-inductor configuration. Furthermore, operation at a fixed frequency is feasible, and hence, feedback control can be eliminated. The fundamental operation is described in this paper. An experimental equalization test was performed for six series-connected SCs to demonstrate the equalization performance. The standard deviation of cell voltages decreased to approximately 5 mV at the end of the equalization process, thus verifying the proposed equalizer's performance.