Hybrid Analysis Method Considering Overhang Structures for Surface Permanent-Magnet Machines

This paper introduces a novel hybrid analysis method based on 2-D finite element method (FEM) for analyzing surface permanent-magnet machine (SPM) with an overhang structure which the axial length of rotor exceeds that of the stator. The overhang results the enhanced torque and power density by simply adding extra permanent magnet (PM) in axial direction utilizing the spare length of rotor compared to the stator with end-turn coil. However, it causes the flux behavior in axial direction especially around end parts of the motor, with inevitably requiring a time-consuming 3-D FEM for the consideration of the non-uniform aspects. It must be computationally big burden for designers to use the 3-D FEM in whole design process. To deal with the problem, a novel analysis method based on 2-D FEM which utilizes a virtual remanence of PM derived from the magnetic equivalent circuit (MEC) analysis is proposed. This concept introduces the MEC considering the overhang effects and combines remanence with a numerical analysis model. The accuracy and usefulness of the proposed method are validated through 3-D FEM and experimental results.