Active Rectifier Design and Synchronization Control for 6.78 MHz Wireless Power Transfer

In wireless power transfer systems, active rectifiers demonstrate improved efficiency and regulation capability. To enable impedance or output regulation, ensure stable operation, and maximize the efficiency, switching actions of the rectifier have to be synchronized with the magnetic field generated from the transmitter coil. This work presents an implementation of a phase-locked-loop synchronization controller using commercial components, including a low-cost microcontroller. A discrete-time small-signal model is used to derive the transfer function of the inherent feedback and design a compensator stabilizing the synchronization loop. Large-signal state-space modeling is used to design a high-efficiency, soft-switching, 6.78MHz power stage. A low-profile, 40W, GaN-based rectifier prototype is designed and built to experimentally verify the ability to synchronize and achieve high efficiency due to soft-switching.