Single-switch cell voltage equalizer based on multi-stacked SEPICs for series-connected energy storage cells

Cell voltage equalizers are usually used for series connected energy storage cells, such as lithium-ion cells and supercapacitors (SCs), to eliminate cell voltage imbalance that may cause premature deterioration and reduce the available energy of the cells. Because conventional cell voltage equalizers are based on multiple individual dc-dc converters, the number of switches, sensors, and/or transformers increases proportionally with the number of series-connected energy storage cells. As compared to conventional equalizers, a single-switch cell voltage equalizer based on multi-stacked single-ended primary inductor converters (SEPICs), which is proposed in this paper, can dramatically reduce circuit complexity because of its single switch operation. Furthermore, feedback control can be eliminated when the equalizer is operated in discontinuous conduction mode (DCM). The fundamental operating principle and the equalization time are mathematically generalized in this paper. An experimental equalization test was performed for four series-connected SCs to demonstrate the equalization performance. The standard deviation of cell voltages decreased to approximately 1 mV at the end of the equalization process, thus verifying the proposed equalizer's performance.