Proposal of a magnetically levitated shaded pole induction motor

Abstract

A magnetic bearing supports a rotary shaft without any contact by magnetic force, but such a system is complex due to additional mechanical and electrical components. In order to reduce the size and complexity of the driving circuit of the bearingless motor, this paper proposes a magnetically levitated shaded pole induction motor. The rotor is still supported by magnetic force, but the motor has a very simple structure because magnetic levitation and rotation can be achieved with only one amplifier. The operating principle of the shaded pole motor was confirmed by FEM magnetic field analysis. The suspension force and rotational torque have also been analyzed. It was found that in order to support and rotate a rotor, large amount of current is required. A simple experimental setup using a commercial shaded pole induction motor was designed and fabricated to verify the validity of the FEM analysis. In the test system, the rotor is supported by a linear rail that allows the rotor free rotation and free movement in a vertical direction but not in a horizontal direction. According to the measured step response, stable magnetic levitation suspension was achieved despite a relatively slow settling time due to the large friction force in the horizontal direction.