An isolated interleaved active-clamp ZVT flyback-boost converter with coupled inductors

The fundamental limitations of interleaved flyback converters for high step-up DC/DC applications are analyzed in this paper. A novel interleaved flyback-boost converter is derived with further modifications on the interleaved flyback converter, which extends the voltage gain and reduces the voltage stress of the switch. The active-clamp circuits are employed to recycle the leakage energy. Both the main and the auxiliary switches can realize ZVT soft switching condition. The turn-off voltage spikes of the main switch are clamped by the active-clamp circuits. Due to the leakage inductance of the coupled inductors, the output diode reverse-recovery problem is alleviated dramatically. A 1 kW prototype with 40V-input-to-380V-output operating at 50 kHz switching frequency built in the lab verifies the effectiveness of the proposed converter. The efficiency of nearly 90% at full load is achieved. More than 7% efficiency improvements with active-clamp circuits are achieved compared with the case with RCD snubbers.