Suspension force investigation for consequent-pole and surface-mounted permanent magnet bearingless motors with concentrated winding

This paper discusses the suspension force of consequent-pole permanent magnet (CPM) and surface-mounted permanent magnet (SPM) bearingless motors with two-independent three-phase concentrated windings for motor and magnetic suspension. Influence of spatial harmonics in the magneto-motive force (MMF) distribution caused by the concentrated winding on the suspension force profile is analytically investigated. We have demonstrated that 12-slot/10-pole SPM bearingless motor produces stable suspension force, whereas 9-slot/8-pole CPM and SPM bearingless motors and 12-slot/10-pole CPM bearingless motor have significant force ripple caused by the harmonics in the MMF distribution. We fabricated a prototype SPM bearingless motor that has three-phase 10-pole and 8-pole concentrated windings in the 12-slot stator for motor and magnetic suspension, respectively. The magnetically suspended rotor was stably driven up to 6000 r/min. In the rotation test, interference of the motor current with the suspension force under loaded and unloaded conditions was not observed.