Dual Constant Voltage Mode Control for Resonant Current Reduction in E-Bike’s Low-Profile Wireless Charging System

This paper focuses on implementing a series-series (SS) resonant wireless power transfer (WPT) with a primary-side resonant current reduction while entering the constant voltage (CV) mode. The prototyping scale and the research methodology are conducted by referring to the electric bicycle (E-Bike) charging applications. Firstly, the basic principles of the WPT system are studied. Then the performance of the resonant tank parameters is analyzed under the switching frequency variation by the equivalent model of the WPT circuit. The conventional CC/CV control method is briefly explained, as well as its limitation. Afterward, the Dual Constant Voltage Mode (DCVM) is proposed to overcome that limitation, resulting in an efficiency improvement when the WPT system enters the light-load condition. Subsequently, the firmware is designed to achieve a practical CC/CV charging mode. Finally, a 200 Watt SS-WPT system with the DCVM optimization is built and experimentally tested in the 20 mm air-gap to verify the theoretical derivation. The power transfer efficiency can reach 90% at the full-load, and the light-load efficiency can be optimized, as the main contribution of this research.