In the high-power energy storage system (ESS), hundreds of battery cells are connected in series to increase the bus voltage, and a battery equalizer is applied to balance the energy of cells. This paper proposes a bidirectional converter-based cell-to-string equalizer with a high-speed balancing algorithm. The performance of the balancing process is verified by 20 series-connected cells with 2A balancing current. The experimental results show that the open-circuit voltages (OCV) of batteries are equalized within 22 mV. The balancing time of the proposed method is reduced by 70% compared to the conventional method.
