A cell selective charge equalizer using multi-output converter with auxiliary transformer

In rechargeable batteries such as lithium-ion, the charge equalization circuit is necessary to enhance life time and guarantee safety. For fast charge equalization, the equalization current is increased as increase of battery capacity, and thus the burden of power semiconductors is increased. Therefore this paper proposes new selective charge equalization circuit with small number of power semiconductors. In the proposed charge equalizer, power diode of transformer secondary side is eliminated and power MOSFET of transformer secondary side is controlled by an auxiliary transformer. By using current unbalance caused by effective voltage mismatching, the charge equalization can be achieved without current blocking switches. In this paper, the operational principle of the proposed equalizer is presented and principle of current unbalance is analyzed. To confirm the validity of the proposed scheme, a prototype of 8 lithium-ion batteries is implemented and experimental results are presented.