Design of High-frequency Resonant Inverter for Capacitive Wireless Power Transfer

This paper presents a novel approach to design a resonant inverter for capacitive wireless power transfer (CPT). CPT, transmitting energy via electric coupling between conducting plates, draws lots of attention because of lighter weight and more compact size than inductive wireless power transfer (IPT) using magnetic fields. This paper proposes a class Φ₂ inverter topology in a small air-gap CPT system to mitigate misalignments in the coupling capacitors. The output capacitor of the load network in the class Φ₂ inverter operates as not only a dc block but also a coupling capacitor in the CPT system. The flexible design process of a class Φ₂ inverter to select the capacitor allows us to maintain high efficiency with any misalignment between coupling capacitors. We also explore different dielectric materials to achieve high capacitance values for coupling capacitors. We present experimental measurements of the capacitors and the push-pull inverter with the measured values of the coupling capacitors. The system's nominal output power was 330 W with a 90% efficiency at an input voltage of 50 V. With the misalignments up to 5 cm, the efficiency is almost constant, 90%, while the capacitance of the coupling plates varies from 6.32 nF to 5.24 nF.