Impedance Matching Network Design for 6.78-MHz Wireless Power Transfer System With Constant Power Characteristics Against Misalignment

Wireless power transfer (WPT) technology has become increasingly popular due to its ability to transmit energy without mechanical contact, making it suitable for various industrial fields. This article deals with an inductive power transfer system, which is driven with a single-switch inverter such as Class E in several megahertz or higher frequencies. One of main issues with such systems is that the output and efficiency are significantly affected by the relative position of transmitter and receiver coils. Many existing solutions require additional tunable components and driving circuits, leading to increased cost and complexity. This article provides a systematic optimization procedure of two-port impedance matching networks for wireless power transfer systems to achieve constant output power characteristics even with misalignment or air-gap variation. Since the system itself has a characteristic that is robust against misalignment, the need for any control and tunable component can be significantly reduced. The effectiveness of the proposed method is verified through a prototype of 6.78 MHz/60 W and experimental results.