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In miniature magnetically levitated rotating machines, permanent magnet bearings are generally used for rotor levitation in the radial directions, while electromagnetic actuators are used for stabilization in the axial direction. Rotor radial oscillations are inevitable in this configuration because no controllable force is applicable in these directions. The oscillations become excessively large as the rotor is running at speeds near the rotor's resonant frequency. This paper presents an implementation and control scheme for an electromagnetic actuator for these machines. The proposed actuator can produce axial as well as radial forces on the rotor. The axial force is used for rotor axial direction control, while the radial force is used to assist in rotor resonance-related oscillation suppression. Theoretical analysis and experimental investigations of the proposed actuator control are performed.
Date of Publication: Feb. 2011