The origin and reduction of acoustic noise in doubly salient variable-reluctance motors

An experimental study of the acoustic noise emitted from an inverter-driven doubly salient variable-reluctance motor (VRM) is presented. A list of possible noise sources is given. Through a series of experiments, all but one source is eliminated as being important, and the remaining source is shown to be dominant. The dominant noise source is the ovalizing deformation of the stator due to its radial magnetic attraction to the rotor. The emitted noise is particularly strong when the frequency of deformation coincides with that of a natural mechanical resonance of the stator. Several methods of reducing acoustic noise emission are studied. One successful method is the introduction of dither into the control of the motor in order to spread the spectrum of noise excitation and reduce its coupling to the mechanical resonance of the stator