Plasma Impact on Overvoltage Short-Circuit Failures in ANPC Converters

Three-level converters experience more complex short-circuit patterns than the standard four types of semiconductor failures for IGBT and / or diode. In literature, there is a special pattern described where three semiconductors in series suffer due to an overvoltage protection that interferes. This happens for saving one of the switches from or against overvoltage in certain situations. However, it is possible that plasma, the free charge carriers inside the semiconductor, is still inside a fourth one as a result of previous switching actions. This allows a second parallel path and impacts the first one. Besides, the plasma itself dissipates over time, which further changes the trend of voltages and currents for the short-circuit situation.