Rotor structure suppressing suspension force ripple in an IPM type bearingless motor with 2-pole motor windings and 4-pole suspension windings

A bearingless motor has integrated characteristics of an electrical motor and a magnetic bearing. In general, surface permanent magnet (SPM) type rotor structure with a ring magnet magnetized in parallel is employed in high-speed PM type bearingless motors. However, in case of increasing motor size for high output, this rotor structure has problems of insufficient suspension force due to a wide air gap and high cost by using the large-diameter ring magnet magnetized in parallel. Therefore, this paper discusses a novel interior permanent magnet (IPM) type rotor structure for the high-speed and high-output bearingless motor. In the novel IPM type rotor structure, suspension force ripple is suppressed by means of arranging flux barriers at the suitable position in a rotor. It is confirmed with 2D-FEM that the proposed rotor structure using the flux barriers is effective in suppressing the suspension force ripple.