Synchronous Rectification for High-Speed Resonant Wireless Power Transfer Under Variable Coupling and Load

A synchronous rectifier (SR) for efficient and compact wireless power transfer (WPT) in applications involving variable coupling, variable load, and lower voltages, e.g., 60 V or less, is presented. The proposed SR employs the load-independent class E topology and a relatively simple synchronization circuit based on a tuned delay line. Analytical, simulation, and experimental results are presented for SRs implemented in resonant capacitive power transfer systems operating at 13.56 and 27.12 MHz. Both systems exhibit load independence over transmission distance variations of $\pm$ 25% from nominal. At 13.56 MHz, 300 W is delivered with a dc-to-dc efficiency of approximately 81% at nominal coupling, which translates to an SR efficiency of 93%, and the system can deliver 220 W over the full coupling range. At 27.12 MHz, 150 W is delivered at a dc-to-dc efficiency of approximately 76% at nominal coupling, translating to an SR efficiency of 89%, and 110 W can be delivered over the full coupling range. The performance of the proposed SR for resonant WPT applications is very encouraging, particularly at 27.12 MHz.