Abstract: Multilevel inverters have been widely applied in high-voltage and high-power applications. Due to the increasing number of the switching devices in multilevel inverter, the probability of fault is increasing simultaneously. The development of reliable systems for fault detection that enable to diagnose a wide range of faults is a motivation of many researchers. In this paper, the theory of IGBT power loss in NPC inverter is introduced and a detecting method of IGBT degradation for diode neutral-point-clamped (NPC) multilevel inverters based on infrared thermography is proposed. Firstly, infrared images of NPC inverter are acquired based on the software FloTHERM and background of the image removed through Otsu’s statistical threshold selection algorithm. Then, the RGB image is turned into a gray image and segmented into small ones. Lastly, hotspots of the image are extracted and an improved detecting method is proposed to diagnose whether the IGBT is in degradation or normal condition. The simulation results prove the feasibility of the proposed method and its advantages in good detecting accuracy.
