1993 Volume 113 Issue 3 Pages 394-402
In recent years, the number of three-phase squirrel-cage induction motors fed by inverters has increased due to the benefits of high efficiency and variable speed control. Motors driven by inverters produce electromagnetic vibrations caused by many time-harmonic voltages as well as by the fundamental voltage. To reduce the electromagnetic vibration, it is necessary to determine the relationship between time-harmonic voltages and electromagnetic vibration.
In this paper, two kinds of time-harmonic voltages superimposed on the fundamental voltage with various phase angles are supplied to the motor at no-load, and the causes of the dominant electromagnetic vibration are analyzed. First, the effects of amplitudes and phase angles of harmonic voltages on the electromagnetic vibration are theoretically studied and characterized. Next, the theoretical results are experimentally verified. It is determined that the characteristics of the dominant electromagnetic vibration can be classified into the following three categories:
(1) the vibration is proportional to the amplitude of one harmonic voltage,
(2) the vibration is proportional to the product of amplitudes of two harmonic voltages,
(3) the vibration varies complicatedly with amplitudes and phase angles of two harmonic voltages.