A Diagnostic Method for Open-Circuit Faults of Loads and Semiconductors in 3L-NPC Inverters

Open-circuit (OC) faults of inverter switch, clamping diode, and load are easily misdiagnosed by most of the existing methods due to the extremely similar fault features. In this regard, a diagnostic method based on line voltage overmodulation and amplitude features is proposed in this article to accurately locate coupling faults of the three-level neutral-point-clamped (3L-NPC) inverter and load. Only two line voltages are used as diagnosis variables, and additional sensor is not required. The proposed diagnosis method consists of two parts: fault detection and fault classification. The fault detective algorithm only requires a small amount of computation and is suitable for uninterrupted execution. The classification algorithm starts immediately when the fault is detected, and the overmodulated voltage features are used to locate the fault. The proposed method can usually complete the diagnosis in 1/4 of the fundamental period. The proposed method is also robust to different modulations, carrier frequencies, and load variations. Experiments demonstrate that the proposed method can distinguish the OC faults of semiconductors (including switches and clamping diodes) and load effectively.