High-Performance Multi-MHz Capacitive Wireless Power Transfer Systems Utilizing Magnetic-Core Coupled Inductors

Matching network inductors in multi-MHz capacitive wireless power transfer (WPT) systems are traditionally implemented using air-core inductors to avoid high-frequency core losses. While air-core inductors can achieve high quality factors, they are large and raise significant electromagnetic interference (EMI) concerns. To address these issues, this paper proposes a magnetic-core-based multi-MHz toroidal inductor structure, capable of achieving comparable quality factors to air-core inductors, while reducing its size significantly. Geometry optimization is performed to determine the optimal physical dimensions of the toroidal structure, resulting in a maximum inductor quality factor. Furthermore, the optimized magnetic-core toroidal inductor is compared with the optimized air-core toroidal inductor in terms of quality factor and size. An example 18 μH magnetic-core inductor designed at 13.56 MHz and 20 A peak ac current using the proposed optimization achieves a quality factor of ~1790, with a 26x volume reduction compared to an optimized single layer winding air-core toroidal inductor of the same quality factor. To validate the theoretical analysis, a 1-kW 13.56-MHz 12-cm air-gap capacitive WPT prototype is tested using the proposed magnetic-core toroidal inductors. Experimental results are in good agreement with the theoretical findings.