Diagnosis of a NPC inverter using Goertzel Filters

Insulated Gate Bipolar Transistors (IGBTs), found in Neutral Point Clamped inverters, can be affected by open-circuit and short-circuit faults. A common mistake found in several papers, from the literature, is highlighted and corrected in this work. The amended method, based on the Park Transform, is extended to isolate the faulty IGBT in a three-level inverter. This method can only pinpoint to one impaired IGBT. Thus, another model-based procedure is presented. The spectrum of the current residuals is analyzed in two different frequency bins, using Goertzel Filters. This method can isolate multiple impaired IGBTs. The two procedures are compared and their results are discussed.