A Low-Cost Multiwinding Transformer Balancing Topology for Retired Series-Connected Battery String

The traditional balance circuit is employed to balance the retired battery string. It will occupy some space for the extra switches, inductors, or/and capacitors of the energy storage system. This letter is trying to share the inductor of the dc-dc converter with the balance system by utilizing the current ripple on the inductor of the multiwinding transformer. The balance circuit does not require additional switches and control logic. The results of dynamic charging conditions show that the circuit is appropriate for balancing the battery string, and the system efficiency with the proposed approach reaches 94.1% at rated 28-W input power. The balance system only increases one diode and one inductor for each cell, which reduces the cost by 60% and 66% separately compared with the traditional resistance equalizer and transformer-based equalizer.