High Power, High Efficiency Wireless Power Transfer at 27.12 MHz Using CMCD Converters

Current-mode class D (CMCD) converters are robust choices for bi-directional wireless power transfer (WPT) due to strong voltage boundary and simplicity at high frequency (HF, 3-30MHz) and very high frequency (VHF, 30-300MHz). A CMCD operating at HF-VHF also enables high power density and circuit integration, but suffers from multiple loss mechanisms that degrade efficiency. Operating at high frequency and high power output presents unique challenges, including parasitic switch losses and WPT coil losses. GaN FETs are the leading candidates for next generation power electronics due to their superior switching speed and power handling capability, but remain a primary factor limiting a CMCD from achieving high efficiency at higher power and higher frequency. In this paper, we investigate the losses that occur in CMCD converters and formulate an optimization procedure to maximize efficiency. This procedure is verified against a full circuit simulation within LTspice. With careful selection of design parameters, the performance of an optimized CMCD can achieve 101.9 W with 89.6% efficiency at 27.12 MHz.