Design and Implementation of a Constant Current and Constant Voltage Wireless Charger Operating at 6.78 MHz

Radio Frequency Wireless Power Transfer (RFWPT) systems operating at higher frequencies such as 6.78 MHz are drawing a lot of attention due to their advantages such as the improved user convenience, the compact size and the light weight. In a WPT charging system the DC/DC converter, which provides an accurate voltage and current to the battery is essential for its safety and lifespan. This paper presents the design and implementation of a high efficiency, light weight-Megahertz WPT system that makes it possible to charge Lithium Batteries by Constant Current (CC) and Constant Voltage (CV) charging with a pair of coils. The proposed WPT charger is simple in structure since it does not require a feedback circuit to implement CC/CV charging. Hence, no communication between the primary side and secondary side is needed. Since the charger can provide automatic mode transfer from CC to CV charging, the battery can be fully charged without the help of an additional DC/DC converter. Simulation and experimental results obtained with a 50W WPT charger operating at 6.78-MHz are presented to verify the feasibility and the validity of the proposed method.