A single-stage single-phase isolated AC-DC converter based on LLC resonant unit and T-type three-level unit for battery charging applications

This paper proposes a four-switch single-phase single-stage isolated AC-DC converter with high efficiency for battery charging applications. By combining one LLC resonant unit and one T-type three-level unit with switch multiplexing technique, a single-stage single-phase isolated LLC resonant (SSPLLC) converter is proposed to achieve AC-DC conversion. In comparison with conventional two-stage isolated AC-DC topologies, the proposed topology works in discontinuous conduction mode (DCM) with small inductor requirement. It can improve both efficiency and power density because of soft-switching capability and wide operating range. The mode analysis, steady-state operation performance and control method are discussed sequentially. Experimental results using a 250W prototype are presented to verify the feasibility and superior performance of the proposed single-stage AC-DC converter.