Single-switch equalization charger integrating SEPIC and equalizer using series-resonant voltage multiplier for series-connected energy storage cells/modules

A single-switch equalization charger, which is a SEPIC integrated with a series-resonant voltage multiplier, is proposed in this paper. The operation of the SEPIC in the proposed equalization charger is identical to a traditional one, while the series-resonant voltage multiplier is driven by an asymmetrical square voltage wave generated at a switching node in the SEPIC. Most of the total charging power is supplied by the SEPIC, while the series-resonant voltage multiplier provides only a fraction of the charging power to eliminate the voltage imbalance. The proposed single-switch equalization charger not only simplifies the circuitry by reducing the switch count but also the system by combining two components (i.e. a charger and equalizer) into a single unit. An experimental charge-discharge cycling test was performed using a 50-W prototype for four supercapacitor (SC) modules connected in series. The series-connected SCs were mainly charged by the SEPIC while the voltage imbalance was gradually eliminated by the series-resonant voltage multiplier, demonstrating the proposed concept and the equalization performance.