A battery equalizer with zero-current switching and zero-voltage gap among cells based on three-resonant-state LC converters

For the conventional switched capacitor converter (SCC) based equalizers, it is difficult to achieve the full equalization among cells due to the inevitable voltage fall across MOSFET switches. Particularly, when the voltage gap among cells is larger, the balancing efficiency is lower, but the balancing speed gets slower as the voltage gap gets smaller. In order to soften these downsides, this paper proposes a battery equalization topology with zero-current switching (ZCS) and zero-voltage gap (ZVG) among cells based on three-resonant-state SCCs. An additional resonant path is built to release the charge of the capacitor into the inductor in each cycle, which lays the foundations to obtain ZVG among cells, improves the balancing efficiency at a large voltage gap, and increases the balancing speed at a small voltage gap. A four-lithium-ion-cell prototype is applied to validate the theoretical analysis. Experiment results show the proposed topology demonstrates good balancing performance with ZCS and ZVG among cells.