A capacitively level shifted fast cell-to-cell battery voltage equalizer

Abstract

Battery voltage equalizer circuit is an essential part of battery-based storage management system. It makes the voltages of series connected batteries equal to avoid overcharging and over-discharging. In this work, a fast cell-to-cell voltage equalizer topology is proposed. The equalizer has a modular structure consisting of one power converter leg for each battery. Capacitors are used to level shift voltage in order to provide capacitive isolation among the converter legs. Converter legs are modulated with sine-triangle modulation and power flow is controlled by phases of these modulation signals. This equalizer can transfer charge among multiple batteries in a string simultaneously or selectively. This topology has been theoretically analyzed and experimentally verified with a prototype.