Design of Robust Capacitive Power Transfer Systems Using High-Frequency Resonant Inverters

This article presents a novel approach using a resonant inverter operating at 6.78 MHz for a robust capacitive power transfer (CPT) system with a small air gap. The flexible design process of a class
$\Phi _2$
inverter to select the capacitance in the load network allows us to maintain high efficiency without a compensation inductor to mitigate misalignments between coupling plates. The capacitor in the class
$\Phi _2$
inverter can be any value above 3 nF at megahertzs frequencies because it is not in resonance but provides dc blocking. If the capacitance value varies in the range above 3 nF, it does not affect the performance of the inverter and the CPT system. We design a push–pull class
$\Phi _2$
inverter to provide isolation between the transmitting and receiving sides by nature and easily increase the output power twice. In addition, compared with the previous CPT system, the proposed inverter can increase the output power, while the misalignment between coupling plates increases because of the nonresonant load network. The designed coupling capacitor with a Kapton film has a capacitance value above 4.6 nF, even with a 15-cm misalignment. We also simulate the design in Ansys Maxwell HFSS to examine the electric fields. We present simulated and experimental measurements of the push–pull class
$\Phi _2$
inverter with the designed coupling capacitor. The system’s nominal output power was 277 W with a 86.65% efficiency at an input voltage of 50 V. With the misalignments up to 15 cm, the efficiency is almost constant, 87% (80% at dc-to-dc CPT system), while the capacitance of the coupling plates varies from 8.82 to 4.62 nF.