LLC resonant converter based on PFM and secondary-side short-circuit control for on-board charger

Commonly used lithium-ion battery on-board charger (OBC) for electric vehicles (EVs) needs a wide output voltage range, but the traditional LLC converter is hard to meet the need under the condition of high efficiency and high power density. In this paper, a resonant converter with hybrid modulation is proposed. The converter has a relatively simple topology and control method. Compared with the traditional LLC topology, only two diodes are replaced by MOSFETs on the secondary side of the transformer, and no auxiliary components are added. The primary-side switches adopt PFM) and the secondary-side switches adopt short-circuit control in the proposed converter, which can realize a wide output voltage range, in a narrow switching frequency range with excellent soft-switching performance. The proposed converter can effectively reduce the resonant current and the volume of transformer core and achieve energy delivery with high power density and high efficiency. The operation principles, voltage gain, and soft-switching conditions of the converter are analyzed in this paper. Finally, a 3.3-kW SiC-based prototype with 400-V input and 250- to 430-V output is built to verify the feasibility and validity of the proposed converter