Analysis of Super High Speed Permanent Magnet Brushless Motor Noise Source and Its Attenuation

Permanent magnet brushless motors are gaining popularity over conventional brushed motors as the industry is constantly requiring for higher efficiency and higher power density high speed electromechanical drivers. Together with advanced bearing and balancing technology, an operating speed of more than 100 krpm is no longer unachievable for commercial motors. However, this achievement comes with a drawback in terms of unpleasant noise level. With increasing awareness of the impacts of noise on human health, several countries start to implement regulatory noise limits on household appliances. In order to market the high speed motors, acoustic performance must be controlled to meet the noise regulations. In this paper, an experimental approach was used to analyze the sound power level of the super high speed permanent magnet brushless motor. The measurements were conducted in a hemi-anechoic chamber equipped with ten microphones. Sound Power Level (LWA) was determined using sound pressure base on ISO standard 3744 (BSI Standards Publication in Acoustics: determination of sound power levels and sound energy levels of noise sources using sound pressure (ISO 3744), 2010 [1]). A correlation between Sound Power Level and the motor's fundamental tone (H1) was observed. Further investigation showed impeller runout was one of the contributing factors to H1. It was proposed to control the Sound Power Level through the controlling of the rotor level impeller surface runout.