500-kHz Operated Three-Phase Grid-Tied Inverter Using GaN-HEMTs Enabled by DCM-Based ZVS Control Utilizing Device Parasitic Capacitance

This paper proposes to apply an off-time discrete control, which is an extension of the average current control for the DCM-operated grid-tied inverters, to a three-phase configuration. It utilizes the oscillation caused by the device parasitic capacitance and the filter inductor, and enables zero-voltage or valley switching with the DCM operations by turning the switches on at the bottom of the oscillating voltage. This paper describes the model used for the operation, and required additional control for the three-phase configuration, which includes the zero sequence control of the filter capacitor voltage and voltage balance control of the two divided dc-link capacitors. The concept was verified using a prototype, which operates with 500 kHz of the switching frequency with the use of a type of GaN-HEMTs. The operation of the three-phase configuration including the zero sequence and the voltage balance controls was confirmed. The turn-on voltage was controlled to be low; therefore, the switching loss could be reduced by the proposed method. It failed in the ranges of phase near to zero-cross of the phase voltage, in which the oscillation period was long, due to decay of the oscillation; however, the turn-on voltages were still low in comparison to the conventional hard switching operations.