Analysis and reduction of acoustic noise from a brushless DC drive

It has been found that stator excitation in brushless DC motor drives can excite mechanical resonances in the motor and, thus, produce acoustic noise in a similar way to switched reluctance drives. A technique has been developed to alter the commutation pattern of a brushless DC motor to avoid exciting and reinforcing these mechanical resonances producing a significant reduction in pure tone acoustic noise which is emitted during mechanical resonance. The origin of the vibration and acoustic noise is explained and the theory of discrete frequency noise reduction described in this paper. The method proposed for quieter control of the brushless DC motor could be achieved at a very low cost.