Inverter Faults In Variable Voltage Variable Frequency Induction Motor Drive Gamal Mahmoud, SMIEEE, Mahmoud Masoud, and Ibrahim El-Arabawy, Senior Member IEEE Alexandria University, Faculty of Engineering, Alexandria Egypt e-mail: Gamal_ mahmoud2003ghotmail.com, mahmoudmasoud77ghotmail.com and Ibr.arabawygyahoo.com Abstract-A simulation and practical results of a common fault occurred in the voltage source inverter used for v/f drive for induction motor, namely; open circuit fault and short circuit fault, are introduced. Results and analysis lead to extract rules for different fault conditions. These rules help for both fault detection and localization. I. INTRODUCTION Now a days, a high percentage of industrial process depends mainly on electric drives. Electric drive consists of rectifier, voltage source inverter or current source inverter, and electric motor. This beside the mechanical load. It is noticed that, any mall function of any semiconductor switch may produce constraints and damage of the control process. Hence, early fault detection and fault location is a must in some application. The rectifier faults are introduced in another research tutorial [1-2]. So, it will be out of scope in this study. Also, motor faults either electrical or mechanical are introduced in many references such as [3-4]. Hence, the motor which is squirrel cage induction motor type and uncontrolled rectifier are considered healthy and has no fault either electrical or mechanical in this paper. The scope of this paper is faults encountered with voltage source inverter (six-pulse 1800 conduction). This is because the voltage source inverter is a common type used in industry applications. Considerable studies within the inverter deals with diagnosis in electric drives are introduced in [5-6]. Kasha in[6]. gave a classification of thinkable faults for voltage source inverter. The faults can be categorized into open circuit faults and short circuit faults. Different methods of fault detection have been developed and analyzed given advantages and disadvantages as in [7-9]. The results are divided into three cases, namely, the healthy case, the open circuit case and short circuit case. The analysis and comparison to healthy case lead to extract an if- then rule which helps to construct fault detection algorithm. The simulation results are validated experimentally. II. INVERTER FAULTS Fig. 1 shows the voltage source inverter stage as fed from rigid uncontrolled three-phase rectifier which can be represented by a battery in this case. The terminal "ABC" is the input terminals to the motor. A switch "SWI" to "SW12" simulates either open circuit fault or short circuit fault. For example, if "SW]" is in open state, this means open circuit fault applied on switch "Q1", and If "SW7" is closed, this means short circuit fault applied on "Ql". This system is built up by the same technique in the laboratory to easy simulating faults. Vdc F2 \swi sw7Fl ,LQl \ F1 F3' tLL 2 1 g SW F 4 F7 FIO Fsw4 0, F4 \s 3 F6 \s 5 Q3 \sw9 r;Q5 ,a-TF5 T A B C IsvL K - Q6 w Q2 F12 .\sw6 , sw2 F11 F13 Fig. 1 VSI Localization of faults configuration III. SIMULATION AND PRACTICAL RESULTS Simulation by using SIMULINK under MATLAB gives the results of the voltage source inverter for the three cases. normally healthy case, open circuit case, and short circuit case. The results of healthy case considered to be "lpu" to compare the faulty results with respect to it, by measuring the root mean square value of fundamental component of motor voltage in different cases. The practical results are given for both healthy case and open circuit case while short circuit case destroy many parts in the drive, mainly the inverter switches and over current protection takes action in this case. As aforementioned, both rectifier and motor are considered to be in a healthy mode during this study. A. Healthy Case A fig.2 part (a) to (c) shows the simulation results of the output voltage of the inverter which at the same time is the input voltage to the motor terminals. The results will be taken as a base result to be compared by the faulty results. Fig.3 shows the practical output voltage. irl.et., ./p ,.ltE:g. vfr ir, healthy case ,~~~~~~~~~~~~~~~ab rms =242- -----X-------- --- -----L------ -- --------X------ [ - 1 ~~~~~~~~i- T 1 1.005 1.01 1.015 1.02 1.025 1.03 1.035 1.04 time- sc (a) 1-4244-1055-X/07/$25.00 ©2007 IEEE. 1-4 v 300 200 100 & 0 .:2 -100 -200 -300