Comparison of Compact Power Amplifier Designs for High Frequency Resonant Wireless Power Transfer Systems at 6.78 MHz using High-Q Resonators

This paper presents a comparison of highly compact power amplifiers for 6.78 MHz, 100 W wireless power transfer systems based on high-Q resonators. The use of multilayer self-resonant structures in the transmission path significantly improves quality factors while maintaining a very compact form factor. This imposes specific requirements on the power amplifier to achieve high efficiencies in a small package. In contrast to the efficient but complex design of a Class Φ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> topology, this work investigates highly compact Class D amplifier designs. Alongside a Current-Mode Class D topology, a ZVS Voltage-Mode Class D/DE topology is introduced, which achieves 93% efficiency at 60 W output power with a highly reduced form factor. Thanks to an additional series resonant circuit at the output, this topology can also be employed for wireless power transfer systems based on high-Q resonators. The size-optimized designs utilize GaN transistors with integrated drivers. At a coupling distance of 2 cm, a coupling factor of 0.2, and a maximum input voltage of 80 V, these amplifiers were tested in a WPT system, achieving up to 70 W transmitted power at 6.78 MHz.