Evaluation of a bearingless PM motor with wide magnetic gaps

A new noncontact drive system has been developed employing a consequent-pole-type bearingless permanent magnet (PM) motor and a thrust magnetic bearing. This bearingless motor has a wide magnetic gap. The wide magnetic gap may cause a decrease in radial magnetic suspension force because of an increase in magnetic reluctance. A thrust magnetic bearing is installed at the end of the shaft because strong thrust force exists in centrifugal pump applications. In this paper, the magnetic suspension forces and rotation characteristics of the experimental prototype are evaluated while the rotor is magnetically suspended. Experimental results are also compared to the calculated ones using the finite-element method. It is demonstrated that the developed consequent-pole-type bearingless PM motor possesses sufficient magnetic suspension force for noncontact operation.