The effects of PWM inverters on the winding voltage distribution in induction motors

This paper gives a detailed analysis of the distribution Of voltage wavefor ms within motor windings generated by a pulse-width-modulated (PWM) inverte r, employing Insulated Gate Bipolar Transistors (IGBTs). These IGBT inverte rs have switching rise times of .05-.2 mu sec and have been, shown to cause insulation stresses and premature motor failures. Experimental work: was p er formed on a comprehensively tapped 5-hp, 460-V, 4-pole induction motor w ith taps from the first and second coil and from the first four and last tw o turns in every phase. Tests were performed using both long and short cabl es with the tapped motor running at rated load. The results of these tests are compared. The extensive tapping of this specially manufactured motor en ables more thorough analysis than has been reported in previous literature. A simulation model, created in PSpice, was used to predict maximum voltage transients across coils and turns and compared with the experimental resul ts.