Multi-Loop Control for Power Transfer Regulation in Capacitive Wireless Systems by Means of Variable Matching Networks

This article introduces an adaptive multi-loop controller for capacitive wireless power transfer (WPT) systems. The new control approach combines continuous frequency tracking and matching networks tuning on both the primary and secondary to regulate a target current/power to the receiving side at the optimal power transfer conditions. This enables to effectively disengage the power delivery capabilities from the cross-coupling interactions between the transmitting and receiving sides and to compensate for variations of the electrical circuits and capacitive medium. This article highlights the complex functional relationships of the multi-mixed-signal controller and provides theoretical as well as practical insights on the dynamics and implementation of a closed-loop capacitive power transfer (CPT) system. The core of the multi-loop controller has been implemented through a digital orientation on an HDL platform. The effectiveness of the new controller is demonstrated on an experimental prototype of a resonant double-sided LC capacitive WPT that has been designed and implemented to operate in the megahertz (MHz) range. The experimental closed-loop operation is well demonstrated under various loads and medium conditions up to 200-mm air gap, validating the self-tuned CPT system. Furthermore, the capacitive interface has been methodically examined through Maxwell's finite-element analysis (FEA) tools for different structures, distances, and alignments. The results of the FEA have been utilized to enhance the accuracy of the experiments, accounting for the variable coupling capacitance under variations.