Evaluation of Magnetic Suspension Performance in a Multi-Consequent-Pole Bearingless Motor

A bearingless motor combines the functions of both noncontact magnetic suspension and torque generation in a single motor unit. Therefore, it offers advantages such as no grease lubrication, no contamination, and can be maintenance free. For low speed rotating and swinging stages (or platforms), the authors have developed a multi-consequent-pole bearingless motor. It has 40 poles and 48 slots with two-pole toroidal suspension windings. The advantage of the multi-pole bearingless motor is its low suspension force variation compared with other bearingless motors with low pole numbers. The aim of this paper is to evaluate the suspension force performance of the bearingless motor. The measured suspension force differed by 21% from the calculated three-dimensional finite element method (3D-FEM) results. It was found that the discrepancy is caused by the number of mesh elements in the 3D-FEM calculation, manufacturing and assembly errors, and the iron stack fill factor.