Hybrid phase-shift-controlled three-level and LLC DC-DC converter with active connection at the secondary side

This paper proposes a hybrid phase-shift-controlled three-level (TL) and LLC dc-dc converter. The TL dc-dc converter and LLC dc-dc converter have their own transformers. Compared with conventional half-bridge TL dc-dc converters, the proposed one has no additional switch at the primary side of the transformer, where the TL converter shares the lagging switches with the LLC converter. At the secondary side of the transformers, the TL and LLC converters are connected by an active switch. With the aid of the LLC converter, the zero voltage switching (ZVS) of the lagging switches can be achieved easily even under light load conditions. Wide ZVS range for all the switches can be ensured. Both the circulating current at the primary side and the output filter inductance are reduced. Furthermore, the efficiency of the converter is improved dramatically. The features of the proposed converter are analyzed, and the design guidelines are given in the paper. Finally, the performance of the converter is verified by a 1-kW experimental prototype.