Coil and Circuit Design of Omnidirectional Wireless Power Transfer System for Portable Device Application

The omnidirectional wireless power transfer (WPT) system has been studied recently due to its better user experience compared with the directional WPT system in consumer electronics application. Wireless charging bowl concept to allow misalignment between transmitter and receiver coil is adopted in this paper. The efficiency of WPT power transmission is related to the magnetic coupling condition and the coil quality factor. Therefore the coil design methodology to achieve high coupling condition and high coil quality factor is proposed. Besides, LCCL-LC resonant converter is a promising topology for omnidirectional WPT application due to coupling and load independent resonant frequency. The parameter design of resonant tank of LCCL-LC resonant converter is focused to achieve three objectives: I. Operating at resonant frequency II. Satisfying output voltage requirement, III. Zero voltage switching (ZVS) turn on. Finally, 6.78MHz omnidirectional WPT system is built and 75∼85% (mostly 80%+) system efficiency at 5W output is achieved for smart phone size receiver in the setup.