Comparative Analysis of Common Mode Voltage, Bearing Current And Shaft Voltage of Diode Clamped SPWM Multilevel Inverter FED Induction Motor

Abstract

Variable Speed Drives (VSD) due to their high dynamic performances are growing importance in industrial applications. PWM inverters are mainly responsible for VSDs dynamic operation but they give rise to bearing currents. Parasitic capacitances present in machine doesn’t create problem at lower frequencies, but at higher carrier frequencies they provide charging path and builds up shaft voltage. When this voltage reaches to a dielectric breakdown voltage of lubricant film, it breaks down, and develops a high discharge bearing current which damage the bearings in a very short time of operation. Multilevel inverter is one of the options to reduce this problem. This paper is an attempt to investigate the effects on CMV, bearing voltage, bearing currents and total harmonic distortion (THD); by diode clamped multilevel (three, five and seven level) and conventional inverter fed induction motor. In this paper phase disposition (PD), sinusoidal pulse width modulation (SPWM) technique is used.