Protection Circuitry Design to Mitigate Failure Propagation for 10 kV SiC MOSFETs in a 22 kV DC 13.8 kV AC Flying Capacitor Multilevel Converter

The operation and failure modes of the flying capacitor multilevel converter topology are well-known and the protections for Si IGBT-based converters are well established. However, when it comes to high voltage SiC MOSFET-based converters there are some particularities that must be evaluated: shorter energy withstanding time, higher dv/dt and higher insulation stress. This paper provides an assessment of the failure modes for a 7-level 13.8 kV AC 22 kV DC 1.1 MVA three-phase flying capacitor converter using 10 kVSiC MOSFETs, an analysis of the fault propagation mechanism between cells and the design of a transient voltage suppressor (TVS) diode-based protection module to prevent it.