Design of active balance circuit for lithium battery pack

This paper proposes a driving circuit for Lithium battery pack with balancing feature. The driving circuit consists of Class-D series resonant converter with multiple series transformers, on which primary windings are connected in series, while secondary sides are loaded by Lithium battery pack. The primary winding and secondary winding are used for the isolation and energy conversion. Zero-voltage switching (ZVS) is operated on the active power switches. Open-circuit voltage measurement method can learn the difference of state of charge (SOC) between the battery cells, which can then estimate the time needed for cell balancing, by the operation of the balanced circuit, the charge of each cell can converge. Therefore, the cells imbalances in battery pack cause the battery to low store utilization problem can be resolved. The prototype circuit is designed for LiFePO4 battery pack (8S1P), and which has been built and tested to verify the analytical predictions.