An Extensive Load Resistor Operation of Wireless Power Transfer System in 13.56MHz Resonant Mode

The variation of load resistor influences the efficiency of the wireless power transfer (WPT) system dramatically. This study designs the mutual inductance of the resonant coil for achieving high efficiency at the heavy load period (20 Omega-50 Omega) and light-load period (50 Omega-120 Omega). A class-E-2 WPT system operated at 13.56MHz is implemented to verify the proposed approach. Measurement shows the efficiency is greater than 76% in a wide range of load resistors (20 Omega-120 Omega). The system output power is 20W at a specified load resistor (30 Omega) which is occurred at a maximal efficiency point.