Acoustic noise from small electronically commutated motors
An analysis of acoustic noise in electronically controlled variable speed drives is presented. The causes of vibration and acoustic noise in switched reluctance motors are discussed and it is shown that brushless d.c. motors can produce resonant vibration and acoustic noise by similar mechanisms. The flux switching motor is introduced. This new class of reluctance motor is an advance on the established switched reluctance motor, retaining many of its benefits, but with a simpler and cheaper power electronic converter. The phase windings and method of flux control are different and tests are performed to quantify the effect on the acoustic noise produced. Measurements of acoustic noise are made on one flux switching motor and one 2-phase switched reluctance motor, made from the same laminations and mechanical components. It is shown that the flux switching motor produced 2dB less acoustic noise under the same conditions. Finite element analysis is used to calculate the radical force profiles of the two motors during normal rotation, and further analysis of this data provides evidence to support the experimental results. The experimental results go on to show how the acoustic noise from a second flux switching drive was found to be comparable to that of a split phase induction motor.