Comprehensive Design for 6.78 MHz Wireless Power Transfer Systems

The call for higher power and larger spatial freedom has driven the operating frequency of wireless power transfer (WPT) systems into the MHz range. Previous system design methods focus on designing the coils to attain high quality factor while remaining resonant around the working frequency and subsequently designing switching circuit hardware and operating point to minimize the system power loss. This sequential design method over-simplifies the system, neglecting inter-dependencies between system components, which leads to suboptimal designs. This paper presents a system design method that co-optimizes coils, power stages, and circuit operation for maximum overall efficiency, based on accurate models of converters and WPT system. The system model and the importance of co-design are verified by a 6.78 MHz WPT prototype.