Generalized IGBT open-circuit fault diagnosis algorithm with no additional sensors for grid-connected N-level NPC converters

This paper presents a real-time diagnostic algorithm for IGBT open-circuit faults in Neutral-Point-Clamped converters, generalized for the N-level case. This algorithm can thus be used in any NPC converter without adaptations, regardless of the number of levels. The algorithm is based on the estimated instant pole voltage error and requires no additional sensors, relying only on signals already available to the controller. The algorithm is independent from the load and control strategy and provides very fast diagnostics, with diagnostic times as low as 2 sample periods (in favorable conditions). Simulation results are presented for the diagnostic algorithm, when used in a NPC rectifier with 3, 5 and 7 levels, showing its speed, effectiveness and robustness.