Transformer-less cell voltage equalizer using switched capacitor voltage divider and series-resonant voltage multiplier for series-connected electric double-layer capacitors

In energy storage systems consisting of series-connected energy storage cells, such as lithium-ion battery cells and electric double-layer capacitors (EDLCs), over-charging and-discharging may occur during charging and discharging under voltage-imbalanced conditions. Various kinds of cell voltage equalizers have been proposed to eliminate voltage imbalance. The equalizer using a voltage multiplier, known as a simple voltage equalizer, utilizes a transformer to generate square wave voltage having an arbitrary amplitude to drive the voltage multiplier. The existence of the transformer, however, impairs the extendibility of the system as it has to be redesigned when the number of series connection of cells is changed. In this paper, the transformer-less cell voltage equalizer using the switched capacitor voltage divider (SCVD) and series-resonant voltage multiplier (SRVM) that can generate square wave voltage having an arbitrary amplitude without a transformer is proposed to improve the extendibility of the equalizer.