GaN-HEMT MHz-Driving Current-Fed Snubberless ZCS High Step-Up DC-DC Converter for Fuel Cell Vehicles

A current-fed step-up dc-dc converter is newly presented in this paper, which is suitable for the front-end high-frequency link dc-dc converter (DC-X) interfacing with a traction motor drive inverter in fuel cell vehicles. The proposed dc-dc converter features the snubberless zero current soft-switching (ZCS) commutation with MHz high frequency switching by adopting quasi resonance and parallel load resonance while minimizing the count of additional circuit components. The switch-mode transitions of the proposed dc-dc converter are explained in details for revealing the principle of snubberless ZCS. In order to obtain the voltage step-up ratio, a time-domain analysis is newly employed for obtaining the high-order harmonics in the three-level stepwise voltage of the quasi-resonant high frequency inverter, which is advantageous over a conventional sinusoidal ac analysis. The effectiveness of the proposed dc-dc converter and the analytical strategy is demonstrated by comparing with the theoretical and simulation results, after which the feasibility is verified by experiment of a 1 MHz-70 W class prototype with Gallium Nitride (GaN) high-electron-mobility-transistor (HEMT).