Influence of Eddy Current in Permanent Magnet Rotor on Suspension Forces and Experimental Verification in Bearingless Motors with Divided Winding

This paper focuses on the influence of eddy current in the permanent magnet (PM) rotor on the suspension force in the bearingless motors with the divided stator winding. In the PM synchronous bearingless motors, the eddy current flows in the PM on the rotor at high speed drives, especially on its surface of PMs. As a result, the uncontrollable electromagnetic force is generated and interferes on the originally commanded suspension force. It makes the rotor levitation unstable and in the worst case, it is seriously concerned that the rotor stabilization unfortunately is not kept. The interference component is mainly Lorentz Forces generated in the PMs by the eddy current. The bearingless motor with 2-pole motor and 4-pole suspension windings (2t4s Belm) and the bearingless motor with 4-pole motor and 2-pole suspension windings (4t2s Belm) have been targeted and compared between the electromagnetic forces in both Belms by the authors. The eddy current in the PMs and the Lorentz Force have been computed by Finite Element Method (FEM) using a simulation software. The difference between 2t4s and 4t2s Belms in the electromagnetic forces, eddy current and Lorentz Force has been found using the FE models and discussed it in detailed. The reason why the rotor levitation is unstable in the 4t2s Belm model has been analytically derived by the simulation. In this paper, it is experimentally verified by a prototype machine of 4t2s Belm.