Analysis of the Audible Noise of Three Phase Squirrel Cage Induction Motors Supplied by Inverters

One of the major problems in inverter fed induction motors is the high level of audible noise produced by harmonic current and voltage components. In order to analyse these phenomena, the field in the machine airgap is calculated using the rotating field theory together with the Maxwell stress theorem. This analysis yields a way for predicting the spectrum components of the electromagnetic noise produced by the motor and relating it to the airgap flux density distribution time harmonics caused by the non-sinusoidal supply. The theoretical approach is used for calculating the airgap flux density distribution and the frequency spectrum components of a small three phase squirrel cage induction motor fed by a six step Voltage source inverter (VSI) and by a pulse width modulated inverter (PWM). The theoretical results are compared with experiments.