Self-balanced Two-output Battery Charger

The design and modeling of a self-balanced two-output battery charger capable to charge two high-power LiFePO4 battery packs is presented. The proposal is based on a four-phase resonant converter, which is designed as a voltage-controlled current-source, working at constant switching frequency. The output stage consists of a transformer with a single primary and two secondaries implementing two current-doubler rectifiers. The structure of the output stage naturally imposes the self-balance-of-charge of both battery packs provided that the coupling between the primary and each of the secondaries has a negligible mismatch. The electrical model of the battery is used to study the batteries charge equalization during the charging process considering the non-idealities of the output transformer. The theoretical analysis and design procedure of the proposed battery charger is fully explained. The output current capability and efficiency are validated experimentally considering a 50 Ah 48 V commercial battery pack.