Non-resonance operations are passively accepted in conventional LLC converters because natural conflicts exist between voltage gain regulation and optimal resonance hold-on. In this paper, resonance hold-on and voltage regulation is simultaneously realized by inserting variable capacitor (VC) in the secondary side of LLC topology, leading to the novel VC-LLC converter whose nominalized voltage gain at resonance can be regulated by adjusting VC capacitance. Analysis and design considerations of the proposed converter are illustrated in detail, especially about implementation of corresponding variable resonance operation (VRO) control. A 400V/314-350V prototype with 1050W maximum power was tested. In contrast to conventional C-LLC converters, efficiencies are holistically improved within the whole voltage gain range under various load conditions in VC-LLC converters with VRO control.

LLC,variable capacitor,resonance