Source of Acoustic Noise in a 12/16 External-Rotor Switched Reluctance Motor: Stator Tangential Vibration and Rotor Radial Vibration

Compared with internal-rotor switched reluctance motors (SRMs), external-rotor (ER) SRMs can show different vibration and acoustic noise behavior due to the differences in the designs, e.g. thinner rotor back iron to achieve smaller inertia, and longer stator pole height to improve the electromagnetic performance. This paper presents the considerations in the modeling and analysis of the acoustic noise sources of an ER SRM stator and rotor. The harmonic components of the stator tangential force density and rotor radial force density are analyzed and compared. The vibration modes, the vibration behavior, and acoustic noise of the stator and rotor are also compared. A 12/16 external-rotor SRM designed for a direct-drive E-bike application is used for the modeling, analysis, and experimental validation of vibration and acoustic noise. It is concluded that both the stator tangential vibration and the rotor radial vibration can be sources of the acoustic noise in an ER SRM.