System fault test of SiC device applied 6.6kV transformerless D-STATCOM

This paper reports the investigation results for transformerless Distribution-Static Synchronous Compensator (D-STATCOM) with Modular Multilevel Converter (MMC) topology. The D-STATCOM has cascaded Silicon-Insulated Gate Bipolar Transistor (Si-IGBT) inverter cells and Silicon Carbide-Junction Field Effect Transistor (SiC-JFET) inverter cells. SiC-JFET inverter cells are operated with Pulse Width Modulation (PWM) since the low switching losses. The Si-IGBT inverter cells have higher DC voltage than the SiC-JFET inverter cells, and they are operated with one-pulse operation that output one positive and one negative pulses during a cycle. MMC topology and high voltage Si-IGBT inverter cells realized connecting the D-STATCOM to 6.6 kV distribution system without transformer. A prototype model of the D-STATCOM rated at 6.6 kV, 100 kVA was built and its field test was executed. The experimental results prove the stable rated operation and Fault-Ride-Through performance.