A Self-Compensated Planar Coil for Resonant Wireless Power Transfer Systems

Compensation capacitors are important components of any resonant wireless power transfer (RWPT) systems and significantly affect the output power, operating frequency, and efficiency. Depending on the compensation network, these capacitors can be placed in series or parallel with the coils. The physical capacitor reduces reliability and increases the size and cost of RWPT systems. Self-resonant RWPT systems have been proposed to remove the physical capacitor, but have to work with high frequency, several megahertz, as reported in existing literatures. In this article, a new planar coil that utilizes parallel-connected multilayer Printed Circuit Boards (PCB) to generate large parasitic capacitance is proposed for RWPT. Both transmitter and receiver coils are made using PCB coils and a spiral winding layout is used to achieve the required inductance and capacitance. Benefit from large parasitic capacitance, the resonant frequency of the proposed RWPT system is reduced to below 200 kHz. Meanwhile, because of the elimination of physical capacitance, the proposed RWPT system has a compact structure, improved reliability, and reduced size, weight, and cost. A coil prototype is designed, constructed, and tested. Simulation and experimental investigations validate the effectiveness of the proposed design.