Safe stop-pulsing strategy for IGCT-based three-level neutral point clamped inverters

Nowadays, the multi-level inverters are widely applied in the high power industrial areas. The direct stop-pulsing method is usually executed during inverters´ normal halt and protection operation, whose reliability is proved in two-level inverters. However, this paper reveals that the direct stop-pulsing method brings risks of over-voltage for switch devices in some multi-level topologies. Regarding this direct method, this paper shows the damaged devices equipped in the 500kW/3.3kV inverter, analyzes commutating mechanism, and represents the actual process in low power experiments. Then, we proposes a safe stop-pulsing strategy for three-level inverters considering the blocking-delay time, the minimum width and the transition of pules. The control flow, determination of key parameters, hardware implementation and related experimental study is described in details.