Performance Comparison of Consequent-Pole and Homopolar Consequent-Pole Bearingless Motors for Low Speed Applications

Abstract

This paper presents performance comparisons of a consequent-pole (CP) and a homopolar consequent-pole (HCP) bearingless motors. Radial directions are actively positioned, and axial and tilting directions are passively stabilized with a disk-shaped rotor. In the CP and HCP bearingless machines, the radial suspension force is generated by a two-pole suspension winding. However, the radial suspension force characteristics are considerably different in the two machines. The radial suspension force of the HCP is generated when a two-pole suspension flux is superimposed on a homopolar flux by thrust permanent magnets. In contrast, the CP bearingless motor requires $p \pm 2$-pole suspension fluxes modulated by the salient-pole rotor core to generate the radial suspension force with a p-pole rotor permanent magnet flux. As a result, the force error angle of the HCP bearingless motor is significantly low compared with the CP bearingless motor. A prototype machine of the HCP bearingless motor is fabricated and tested. In the experiment, it is demonstrated that stable magnetic suspension and rotation are achieved at 1000 r/min.