Synchronous Push-Pull Class E Rectifiers with Load-Independent Operation for Megahertz Wireless Power Transfer

This paper presents the analytical modeling of synchronous class E rectifiers with the load-independent operation, which achieves zero-phase-angle input impedance, soft-switching over the entire load range with a constant voltage gain. The optimal design of the synchronous class E rectifier is proposed to realize both of zero-voltage-switching turn-on and zero-current-switching turn-off at the expected output power. An LCC-S compensated MHz-WPT topology, which comprises the push-pull class E inverter and rectifier with the load-independent operation, is proposed to achieve the fully soft-switching and a nearly-constant voltage gain over the entire load range. The efficiency improvement of the compensation network is also investigated to provide a design methodology for the proposed topology. A 6.78-MHz WPT prototype, along with an alternative phase detector using an auxiliary coil to realize phase detection, is built to validate the analytical model and the proposed methodology. The system efficiency reaches 86.7 % at 214 watts output. The synchronous push-pull class E rectifier maintains soft-switching over the load range, and the rectification efficiency reaches 94.6 %.