Closed-loop Control of a Dynamic Capacitive Wireless Power Transfer System

This paper introduces a closed-loop control strategy to dynamically compensate for coupling variations in capacitive wireless power transfer (WPT) systems utilizing an active variable reactance (AVR) rectifier. The AVR rectifier provides this continuously variable compensation, and maintains full power transfer at high efficiency, by appropriately splitting power between its two branches while operating at a fixed frequency. The proposed control approach utilizes a decoupled-dual-loop strategy to regulate the power in the two branches of the AVR rectifier. This approach enables dynamic reactive compensation and output power recovery under misalignment conditions without needing to sense any high-frequency voltage or current. A 6.78-MHz scaled capacitive WPT prototype, incorporating an AVR rectifier controlled using the proposed approach, is designed, built and tested. The proposed closed-loop control strategy enables the prototype system to maintain constant output power for large misalignments between the coupling pads.