Fault-tolerant inverter for subsea applications

This paper investigates in a topology of medium voltage inverter retained to guarantee severe conditions concerning environmental and reliability requirements. This system is based on a standard three levels NPC (Neutral Point Clamped) drive with redundant IGBT and can tolerate the on-state failure mode of the IGBT. Like this, in the operation mode the inverter has been designed to run in permanent condition with a failed IGBT in short circuit. The failed IGBT have been observed and analyzed in order to estimate the short circuit stability. On the other hand, the material improvement such as cooling unit, gate drive, control system and components sorting have been carried out to increase the design lifetime but will not be presented in this article. An experimental 200 kVA mockup have been carried out and will be presented such as the significant results to qualify the principles.