Challenges and Comparison in Achieving 6.78 MHz Multi-kW H-Bridge DC-AC Inverters Using High-Voltage SiC and GaN Switching Devices

This article investigates the challenges of designing 6.78 MHz multi-kilowatt H-bridge inverters with high-voltage silicon carbide (SiC) and gallium nitride (GaN) devices, while comparing their performance. First, a design methodology for MHz-switching H-bridge inverters is proposed, addressing critical aspects such as switch selection, gate driver supply design, parasitic inductance minimization, zero-voltage switching, and thermal management. Three 1st-generation inverters are then implemented using 650 V wide-bandgap devices: SiC MOSFET (C3M0060065K), GaN field-effect transistor (FET) (TP65H070G4PS), and GaN FET (GS66506T). In multi-MHz and multi-kW testing, the SiC-based inverter reaches a switching limit of 4 MHz at 3.874 kW but suffers from gate driver overpowering and thermal constraints. The TP65H070G4PS GaN inverter achieves the optimal frequency-power balance, delivering 2.026 kW at 6.78 MHz, though it exhibits significant oscillations at low dc voltages (<250 V). Meanwhile, the GS66506T GaN inverter demonstrates superior high-frequency performance but struggles with thermal dissipation, attaining 1.105 kW at 6.78 MHz. To enable reliable 6.78 MHz power conversion, a 2nd-generation design is developed using enhanced SiC (C3M0120100K) and GaN (GS66508T) switches and evaluated in a 6.78-MHz and 2.4-kW isolated dc-dc converter. These inverters achieve 2.448 kW with 93.63% dc-dc efficiency for the SiC inverter, while the GaN variant reaches 2.483 kW at 95.17% efficiency. This marks the first practical demonstration of a multi-kW SiC H-bridge inverter operating at 6.78 MHz and highlights the performance tradeoffs between SiC and GaN technologies. © 2025 IEEE.