6.78 MHz Wireless Power Transfer with Self-Resonant Coils at 95% DC-DC Efficiency

MHz-frequency inductive wireless power transfer holds promise of compact and efficient wireless power transfer. Unfortunately, due to high-frequency losses in wide-bandgap semiconductors and low-Q high-frequency coil designs, these systems are universally less efficient, on a dc-dc basis, than wireless power systems operating at conventional frequency regimes. This letter describes the design considerations for inductive wireless power transfer systems operating at 6.78 MHz. With a novel high-frequency resonant amplifier topology, a high-Q self-resonant coil structure, and a better understanding of Coss losses in wide-bandgap power semiconductors, we demonstrate 6.78 MHz wireless power transfer systems that achieve 95% dc-dc efficiency at power levels up to and beyond 1 kW.