A utility interfaced half-bridge based capacitively coupled power transfer circuit with automatic frequency control

This paper describes a capacitively coupled power transfer (CCPT) circuit for higher power application. The circuit has a static transmitter powered from the utility and a movable receiver. Two plates between the transmitter and receiver form a capacitive power transfer surface. A ceramic based dielectric between the parallel plates is realized using low-cost surface-mount ceramic capacitors. Unity power factor (UPF) interface is at the front-end of the circuit to comply with utility regulation requirements. The inversion circuit uses a half-bridge topology to reduce complexity and a series resonance circuit to optimize power flow between input and output. A simple automatic frequency control circuit acts as a phase lock loop (PLL) and tracks the resonant frequency as a function of the mobile receiver placement and based on this information the half-bridge inverter is switched. A 35 W prototype is used to verify the proposed concept.