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 C<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oss</inf> 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.