Systematic Design of a 100-W 6.78-MHz Wireless Charging Station Covering Multiple Devices and a Large Charging Area

This article details the systematic design of a 100-W multiload wireless charging station. The station provides positional flexibility for the receivers, exhibits limited cross-channel disturbance, and has high efficiency. The positional flexibility is achieved using a transmitter coil design approach, which uses interleaved windings and controlled coil geometry to shape the magnetic field. The limited cross-channel disturbance is realized with an immittance network, which maintains a constant transmitter coil current. A holistic system-level modeling and design method is proposed to design the entire system for maximum efficiency. The first step is decoupling each stages using parameterized source and/or load of adjacent stages, and optimize internally for minimum loss, which leads to a reduced design space. The second step is system-wide optimization, which addresses power loss interdependence. A 100-W, 6.78-MHz experimental system with a 0.5 × 0.5 m$^2$ transmitter coil is demonstrated. The measured magnetic field variation on the charging surface is 15.9%. And the system shows no cross-channel disturbance when charging two 50-W receivers. The measured dc-to-dc efficiency is 92.8%.