Design of High-Efficiency Matching Networks for Capacitive Wireless Power Transfer Systems

Matching networks are an efficient means of providing large voltage or current gain and reactive compensation in high-frequency wireless power transfer (WPT) systems. This article introduces an analytical optimization approach for the design of L-section matching networks in capacitive WPT systems, which maximizes the network efficiency while achieving the required overall gain and compensation. The proposed approach identifies the optimal number of matching network stages and the optimal distribution of gains and compensations among these stages. Compared with the conventional approach to designing matching networks for capacitive WPT systems, the proposed approach results in higher and flatter efficiency for a wide range of air-gap voltages. The proposed approach also offers a better tradeoff between efficiency and power transfer density while meeting electric field safety requirements. The efficiency predictions of the proposed design approach are experimentally validated using three 6.78-MHz 100-W prototype capacitive WPT systems: one with single-stage matching networks, one with two-stage matching networks, and another with three-stage matching networks. The measured matching network efficiencies of the prototype systems are in close agreement with the theoretical predictions. The prototype system with two-stage matching networks is also compared with a prototype system designed using the conventional approach and is shown to achieve significantly higher efficiency.