Design and Performance Comparison of Multi-Frequency Inductors for Megahertz Wireless Power Transfer

In MHz inductive power transfer, inductors are crucial parts of the primary coil driver circuitry but, given the highly efficient Gallium Nitride (GaN) devices, dominate the losses. These inductors must often conduct current at multiple frequencies, making it challenging to design them with low loss. In this paper, we provide a streamlined process for designing low-loss inductors for multi-frequency MHz applications that leverages a previously-developed modified pot (MP) core structure. Using this design process, we design an MP inductor and integrate it into the ϕ-branch of a 13.56 MHz, 70 W Class EF 2 inverter, which conducts significant current at the fundamental, second and third harmonics. We quantitatively evaluate its performance by conducting a comprehensive comparison with a variety of air-core and ferrite-core inductors. The power losses in the MP inductor were less than half that of the matched comparison air-core and cored inductors, which resulted in a 0.4% increase in system efficiency over the best comparison inductor, corresponding to a 6% reduction in total system loss.