Conference: 2020 한국자기학회 동계학술대회
Authors: 김재현, 박수환, 박민로, 이수경, 차경수, 임명섭
DOI:
Since electric motors with outer rotor have advantages such as higher torque density and less joule loss compared to electric motors with internal rotor, electric motors with outer rotor are widely used for various applications. The noise of the electric motor with outer rotor is one of the most important performance indicators especially when it is used for home appliances. Generally, the noise of the electric motor caused by the radial electromagnetic force acting on the outer part of the electric motor. As shown in Fig. 1, in the case of the electric motor with internal rotor, the radial force acts on the stator, which is a fixed part. On the other hand, in the case of the electric motor with outer rotor, since the radial force acts on the rotary part, the relative speed of the radial electromagnetic force and the rotor should be considered.
Therefore, in this paper, the frequency and spatial harmonic order of the radial electromagnetic force acting on the rotor of electric motor with outer rotor are analytically derived. The sources of the radial electromagnetic force are analytically derived by dividing it into permanent magnet (PM) magneto-motive force (MMF), armature reaction MMF, and slot effects. The frequency and the spatial harmonic order of the radial electromagnetic force acting on the rotor are summarized in Table I. Noise test of the prototype was conducted to validate the analytically derived results as shown in Fig. 2. The prototype is 48 pole 36 slot electric motor with outer rotor for direct drive system. The frequency of the radial electromagnetic force acting on the rotor is generated as multiple of 1.5f, as can be derived from Table I. This result corresponds well with the noise test result as shown in Fig. 2. (b).