5th International Conference on Automation, Control Engineering and Computer Science (ACECS-2018) Proceedings of Engineering & Technology (PET) Experimental Study of Inverter Open-Circuit Fault Diagnosis using Stator Current Spectrogram Bilal Djamal Eddine CHERIF #1 , Azeddine BENDIABDELLAH #2 , Mokhtar BENDJEBBAR #3 # Diagnostic Group, Laboratory LDEE, Electrical Engineering Faculty, University of Sciences and Technology of Oran BP 1505 El-Mnaouer Oran 31000, Algeria 1 bilal.cherif@univ-usto.dz 2 bendiazz@yahoo.fr 3 bendjebb_dz@yahoo.fr Abstract— Three-phase static converters with voltage structure are widely used in many industrial systems. In order to prevent the propagation of the fault to other components of the system and ensure continuity of service in the event of a failure of the converter, efficient and rapid methods of detection and localization must be implemented. This paper work addresses a diagnostic technique based on the time-frequency representation called Short Time Fourier Transform or Spectrogram (STFT), for the detection of an inverter IGBT open-circuit switch fault. To illustrate the merits of the technique and validate the results, experimental tests are conducted using a built three-phase voltage inverter fed induction motor. Keywords— Inverter, diagnostic, detection, open-circuit, STFT, spectrum I. INTRODUCTION Three-phase static converters voltage structures are widely used in many power applications. Continuity of service of these systems and their safety, reliability and performance are of major concerns today. Indeed, the failure of the inverter can lead to loss of control of the phase currents resulting in serious system malfunction or even a complete stop. To prevent the spread of the fault to other system components and ensure continuity of service in all circumstances, upon failure of the inverter, the converter topologies fault tolerant associated with effective and rapid methods of detection and localization failure must be implemented. Several researchers have carried out their investigation in relation to the field of detection and localization of faults in static converters and more particularly those related to three phase power inverters [1]. The treated fault is mainly concerned with the open-circuit fault of an inverter IGBT switch [2]. Most published papers are based on Park's current vectors approach [3]. This approach is based on the trajectory tracking of the phase current vector. In fact, for the case of a healthy state condition of the inverter, the trajectory of these current vectors in the (d-q) frame is a circle. It was found that the circle becomes a semicircle under an open-circuit IGBT switch fault in one of the legs of the inverter. The position of this semicircle in the (d-q) frame makes it possible to identify the faulty IGBT switch [4]. Another paper used the mean value of the phase currents in Park's frame for the extraction of the open-circuit fault angle of each IGBT switch [3], [4], unfortunately this method presents an inconvenient as it depends on the load. To overcome the problem some authors suggested the normalized DC current method which is fundamentally based on the dc component of the current and the first order harmonic coefficients of the ac-currents [5]. Some detection techniques mentioned above are briefly discussed in reference [6], [7].To overcome this constraint, it is necessary to use a time-frequency representation. Indeed, the Gabor works in the 40s have led to the foundations of a new type of analysis called Short Time Fourier Transform (STFT) or spectrogram. He was the first to imagine a local Fourier transform based on a windowing signal analysis to observe changes in frequency with time. This transformation requires the division of the signal in consecutive short segments and then calculates the Fourier transform of each segment. The idea is to introduce the local frequency parameter so that the Fourier transform is applied to the signal through a sliding window on which the signal is approximately stationary. This method represents the results into three dimensions; the description of the signal is carried out in the time-frequency plan composed of spectral characteristics as a function of time [8]. This paper presents an approach using the technique based on the spectral analysis (STFT) to investigate the detection of the harmonic characterizing the IGBT switch open-circuit fault and localization. This approach addresses the STFT technique to extract the information related to the harmonic characterizing the open-circuit IGBT switch and presents the various experimental results and their interpretations. II. VOLTAGE SOURCE INVERTER STRUCTURE Fig 1 shows the structure of a three-phase two-level voltage source inverter feeding an induction motor. D1 D2 D3 D4 D5 D6 K1 K2 K3 K4 K5 K6 L C A B C INVERTER LOAD RECTIFIER M Fig. 1. Structure of a three-phase two-level inverter