1 Fault Diagnostics in an Inverter Feeding an Induction Motor KHATER, Faeka and ABU EL-SEBAH, Mohamed Electronics Research Institute - Dokki, Cairo, Egypt OSAMA, Mohamed High Institute of Engineering – Six October City, Egypt Abstract This paper presents a fault diagnostics system for a three-phase voltage source inverter. The system is developed as a rule-based fuzzy logic system for fault cases of the inverter power semiconductor switches. Based on a time domain simulation model, the inverter different fault conditions are simulated with the resulting voltage spectrum providing the database for the fuzzy logic system. The developed fault diagnostics system is capable of identifying the type and location of the inverter fault. Keywords: fault diagnostics, voltage source inverter, fuzzy logic 1 INTRODUCTION Inverter use is popular in modern industrial, aerospace, traction, residential, etc.… systems and power plants in the present time. The induction motor (IM) is the most applicable motor type in variable speed AC drives, therefore reliability of the inverter feeding an induction motor is of great importance. To keep the inverter reliability at a high level, fault diagnostics is required to allow controlled shut down in order to reduce both outage time and damage of equipment, and to permit scheduling in preventive maintenance. Therefore, monitoring and control is not only required to switch off the drive system in a safe way, but detection of the fault location and seriousness enables use of standby equipment or modification of the operation strategy [1-3]. Online diagnostic techniques require the use of the available sensors in the drive system for economical reasons. Although several techniques have been developed for fault diagnostics (FD) and fault diagnostics model in the induction machine [4-7], very limited work has been carried out to investigate fault diagnostics in the inverter. This deficiency provides the interest to propose an adequate method to determine the fault type and its location in the inverter. Detection techniques have previously been introduced for open-switch FD in the voltage source inverter (VSI) fed a synchronous machine drive system. The techniques utilize measurement of voltages at key points of the drive system and an analytical model [2]. Detection based on knowledge model is presented for a PWM inverter supplying a synchronous machine [8]. The diagnosis system used two approaches, the current-vector trajectory or the instantaneous frequency to detect and identify the fault of an open transistor in the inverter. A knowledge-based expert system approach has been presented for fault diagnosis of a 3-phase inverter except the fly wheeling diodes [9]. Such diagnosis was based on the most probable defect since the measurement information with Fourier analysis was not able to result explicit determination of the fault. In [10], an expert system based fault diagnosis for VSI fed ac motor was presented. The system defined only the fault type using a fault tree configuration of the VSI, motor and mechanical faults on-line or off-line (trouble shooting & repair). The on-line diagnosis is based on the input & output measurement of each device that results the type of fault. Fault modes of VSI for IM drive were investigated for the key fault types [1]. A few selected fault types were mathematically analyzed and verified by simulation for open loop volts/hertz control of the drive. This study can be useful for prediction of post-fault operation and fault tolerance control. A survey on some diagnosis methods, for First page Template Secretariat uses only. Do not type in this box. The International Conference on Electrical Engineering 2008 No. O-011