Design and Implementation of a 6.78 MHz GaN HEMT H-Bridge Inverter with Auxiliary Inductor-Enabled ZVS

The advancement of gallium nitride (GaN) semiconductors has pushed power converters to operate at multi-megahertz (MHz) frequencies for high compactness and power density. As for a multi-MHz GaN-based H-bridge inverter, the GaN devices generally encounter difficulty in achieving zero-voltage-switching (ZVS), which may cause significant switching loss, thermal issues, and inverter oscillations. This paper presents a 6.78 MHz GaN high-electron-mobility transistor (HEMT)-based H-bridge inverter with an auxiliary ZVS circuit employing a single copper-wound air-core inductor with low equivalent series resistance (ESR), which can produce the inductive reactive power to compensate the capacitive reactive power generated by the Coss of GaN devices without inducing significant power loss, enhancing the ZVS achievability and reducing hard-switching loss of the inverter. Experimental results demonstrate that under a fixed load of 115Ω, ZVS is only achieved at input DC voltages of 200 V or above when the auxiliary circuit is not implemented; however, utilizing an auxiliary inductor of 2.82 μH, the ZVS operation threshold of the input voltage can be reduced to 150 V with improved efficiency in hard-switching, validating the effectiveness of the proposed auxiliary ZVS circuit.