Numerical simulation of electromagnetic vibration of small induction motors

Motors with low noise characteristics are increasingly in demand due to environmental considerations. The primary source of noise of these motors, in particular of the most widely produced 4- and 6-pole induction motors, is electromagnetic vibration. To gain a better understanding of this specific kind of vibration, the relationship between magnetic flux and mode of vibration is examined from a study of electromagnetic forces and the motor's mechanical response. The flux distribution of the motor is calculated by a finite element method (FEM), and from the results of this study, flux density over the motor's radial direction is analysed in the space and time domains. Similarly, the electromagnetic force waves are calculated by the Maxwell stress method and FEM analysis in the space and time domains. Using Fourier analysis, harmonics of these forces are obtained, and are subsequently used as applied forces in the study of mechanical vibration. The vibration behaviour of the motor caused by electromagnetic forces is simulated using FEM for structure analysis. The modes and amplitudes of vibration provided by these calculations are then compared with experimental results and the strong influence of the frequencies close to natural frequency on the modes of vibration is confirmed.