An active cell-to-cell balancing circuit with planar coupled inductors for series connected batteries

The active cell-to-cell equalizers can achieve energy transfer between two cells, which may be an effective equalization method in some battery applications. This paper proposes a new direct cell-to-cell active equalizer using planar coupled inductors. The new circuit allows the energy to transfer directly between any two cells by fly-back operation or Buck-Boost operation which gives a short balancing path and guarantees a fast equalization speed. The planar coupled inductors are adopted for high power density. The results of balancing test with a six-20Ah Lithium-ion battery string show the validity of the circuit.