Active Cell Balancing of Li-Ion Batteries Using Series Resonant Circuit

This paper proposes a new active cellbalancing method for Li-ion batteries. It uses an LC series resonant circuit as an energy carrier, which transfers the balancing energy directly from the highest charged cell to the lowest charged cell. The method requires N + 5 bilateral switches and one LC resonant circuit, where N is the number of cells in the string of batteries. The balancing speed is improved by allowing energy transfer between any two cells in the battery string, and power consumption for balancing is reduced by operating all switches in the circuit at a zero-current switching condition. An experimental cellbalancing circuit for a 12-cell Li-ion battery string shows that fast and transformerless balancing is possible using the proposed method. Measured power transfer efficiencies were 93.2% and 78.9% at balancing powers of 0.56 and 1.94 W, respectively.