Electromagnetic Forces in Induction Motor With Nonsinusoidal Power Supply.

Abstract

Magnetic flux density and electromagnetic forces of induction motors at sinusoidal and nonsinusoidal power supply are analyzed. On the basis of asymptotic small parameter expansions depending on the level of higher time harmonics in the supply current waveform the most essential components of radial and tangential forces are singled out. With the given current waveform preliminary estimations of the relation of electromagnetic forces and torques of geometrically similar motors are obtained. It is shown that even insignificant distortions in the supply current waveform may bear negative effect on increase in vibrations due to some additional torques and forces. These forces are conditioned by interaction of the main field and linear load waves from the current first and higher time harmonics. In relative units they are comparable with forces of interaction of the field tooth harmonics. Increase in the current harmonics leads to proportional increase in electromagnetic forces. At significant current harmonics some additional rise of the total level and enrichment of the spectrum of forces due to interaction of the field higher time harmonics between themselves takes place. The computation results are compared with the experimental data for an induction motor power supplied from a pulse-width frequency converter.