Two-pulse Width Modulation for Voltage Regulation and Reduction of Electromagnetic Field Radiated by Third Harmonic Current in Wireless Power Transfer System

Recently, wireless power transfer (WPT) for electric mobilities has much attention. The electromagnetic field radiated by the WPT current is limited by the international regulations. In order to reduce the electromagnetic field radiated by the third harmonic current (3rd-EMF) in an SS topology WPT system, the inverter is often operated using a phase shift control whose shifted phase is fixed at π/3 rad. However, an additional DCDC converter is needed to control the WPT power. This paper proposes the two-pulse width modulation method to achieve both the voltage regulation and the 3rd-EMF reduction. The switching timing is determined by calculating the Fourier transform of the inverter output voltage waveform. The proposed method is experimentally validated using a GaN inverter which is used to generate the precise voltage waveform. The results show that the proposed method can regulate the voltage and reduce the third harmonic current simultaneously. The inverter efficiency is more than 92% when the duty ratio is more than 50% even if hard switching is conducted.