Switching-Frequency Limitations of a Three-Phase PWM Inverter using Si-MOSFETs and SiC-SBDs

This paper focuses on a three phase PWM inverter using Si-MOSFETs and SiC-SBDs (Schottky Barrier Diode), and discusses the limitation of high-frequency switching operation on the basis of both the loss and thermal resistance analyses. As a result, the thermal-resistances of the MOSFET should be as small as possible because the switching losses of the MOSFET are dominant in the total loss for switching operations greater than 100 kHz. This paper presents a circuit implementation procedure based on separating the heat sinks in each MOSFET. The experimental results, rated at 300 kHz and 3.2 kVA, are presented for verifying the proposed implementation procedure. Finally, the switching frequency limitations are discussed considering among the thermal resistance, the switching frequency and the dead time of the inverter.