Effect of the Conduction Resistance of SiC MOSFET on the Harmonics of Inverter Voltage in Wireless Power-Transfer Systems for Electric Vehicles

This paper describes the effects of power device characteristics on the harmonics of the inverter output voltage and magnetic field leakage in a wireless power transfer system for electric vehicles with phase shift control and the suppression method of the haemonics. Even when the phase shift angle is theoretically set to minimize harmonics, the experimental results have confirmed the existence of the remaining harmonics, which have dead-time dependence. Harmonics with dead-time dependence include those caused by changes in the pulse width depending on the dead time, which have been conventionally compensated for by dead-time compensation. However, the targeted harmonics have a dead-time dependence even when the pulse widths are matched. Therefore, we focused on the difference between the dead-time period and other periods. Further, as the conduction resistance differs between these two periods, we performed a circuit analysis, also considering the conduction resistance. From the results, it was theoretically clarified that harmonics are generated because of the difference in resistance in the forward and reverse directions of power devices. Furthermore, the theoretically calculated dead time dependence of the device-induced harmonics was confirmed by experimental measurements of the harmonics of the inverter output voltage waveform and the magnetic field leakage. This confirms that one of the factors responsible for the harmonics is the difference in the device conduction resistance before and after the dead-time period. The main contributions of this paper are the revelation of unconventional dead-time-dependent harmonics and the proposal of a method for suppressing them.