Magnetic noise reduction of induction machines

A method has been developed which allows a reduction in magnetic noise of induction machines by injecting current harmonies. Its achievement needs an accurate knowledge of the flux density harmonics in the airgap of the machines. First, the principle of the magnetic noise generation is reviewed A fictitious slot model allows us to determine the airgap permeance expression and, multiplying this last one by the expression of the magnetomotive force distribution, to define the flux density harmonics. The stator harmonics are described. They induce electromotive forces and currents into the rotor conductors which generate rotor flux density harmonics. The knowledge of those quantities allows to calculate the Maxwell. forces which can generate magnetic noise. A method of noise reduction is then explained. Its principle is to inject a small controlled current harmonic into the stator windings in order to create a supplementary force wave which opposes those contributing to noise. A small supplementary current allows a reduction of magnetic noise in a big machine. The method limits, precisions, calculations, control. principles and injection ways, are described in order to know if the noise of a motor can be reduced and how to do it. Experimentations illustrate those descriptions.