Three-Phase LLC Battery Charger: Wide Regulation and Improved Light-Load Operation

Three-phase LLC resonant converters can handle much higher power compared to half-bridge and full-bridge LLC converters, which makes them suitable for levels 2 and 3 battery charger applications. In addition to the unique features of LLC resonant converters, the three-phase structure provides higher power capacity and higher power density at higher power levels in comparison with single-phase structures. Although single-phase LLC resonant converters were thoroughly investigated in the literature for many different applications, limited work has been done on three-phase LLC converters. Unexplored problems with three-phase LLC resonant converters include issues with their limited gain range and also their poor light-load efficiency. In this article, a modified three-phase LLC resonant converter with a new phase-shedding strategy is proposed. With the proposed modified topology and phase-shedding strategy, the wide gain range needed for covering the recovery zone of charging Li-ion batteries is realized. Moreover, with the proposed phase-shedding strategy, a significant efficiency improvement with light-load absorption charging is achieved. A $\text{3-kW}$ prototype was developed to validate the performance of the proposed converter.