Comparison and Design Optimization of Consequent-Pole and Multi-Monopole Surface Permanent Magnet Bearingless Motors

This paper presents performance comparisons of consequent-pole and multi-monopole surface permanent magnet (SPM) bearingless motors. These topologies do not require rotor rotational angular positions for the magnetic suspension. The force error angles must be small, otherwise the levitated rotor would be touched down on the stator. In fact, it is difficult to design the magnetic circuit to reduce the force error angle in the consequent-pole bearingless motor because the air-gap flux density includes modulated fluxes due to a salient-pole rotor core. In this paper, it is verified that the proposed multi-monopole SPM bearingless motor has great performances of high radial suspension force and low force error angle compared to that of the consequent-pole rotor. In addition, the design optimization is presented with respect to pole/slot combinations and several geometrical parameters of the rotor and the stator.