Active clamped current-fed full-bridge converter integrating LLC converter with low current and voltage stress

Abstract

Today, Renewable energy based clean distributed power generation systems are widely employed due to the concern about environment. Fuel cell is one of promising clean energy sources. Fuel cell power supply system typically includes a high step-up converter to boost the output voltage of fuel cell stacks. Active clamped current-fed full-bridge converter is widely used in low input voltage application. In low input voltage application, the low efficiency is caused by the high conduction loss of main switches ($S_1$ - $S_4$). In additional, high turn-off current flows through the auxiliary switch ($S_{aux}$) generating the large turn-off switching loss. Moreover, since auxiliary switch operates with doubled switching frequency, the turn-off loss is accelerated. This paper proposes active clamped current-fed full-bridge converter integrating LLC converter for fuel cell power system. LLC converter is integrated into conventional active clamped current-fed full-bridge converter without additional active component and volume increasing. Due to the two transformers structure, peak current of main switches $S_1$ - $S_4$ is reduced. Conduction loss of main switch is decreased. Moreover, Turn-off loss and conduction loss of auxiliary switch $S_{aux}$ is reduced by sinusoidal resonant current. In addition, the proposed converter has low voltage stress on the primary switches because a high step-up voltage conversion ratio can be realized with the low duty ratio D. Thus, Switches can be selected with low $R_{DS(on)}$. To verify proposed converter performance, prototype converter with 36V-57V input voltage, 400V output voltage, and 1kW output power is implemented.