A Lumped Magnetic-Circuit-Model-Based Analysis Method for Surface Permanent-Magnet Machines with Rotor Step-Skewing and Overhang

This study proposes a new analysis method based on lumped magnetic-circuit model for surface permanent-magnet machines with rotor step-skewing and overhang. The rotor step-skewing technique produces lower torque pulsation and sinusoidal back-EMF. In addition, an overhang structure having an extra rotor magnet in the axial direction provides enhanced torque and high power density. However, the three-dimensional (3-D) phenomena observed in the axial leakage flux between the skewed steps and the linkage flux owing to extra overhang magnet requires a 3D finite element method (FEM), which needs a considerable computation time and memory. To deal with this problem, a new equivalent lumped magnetic-circuit model for each rotor step considering the axial leakage flux between the steps and the linkage flux by the overhang is introduced. In addition, a new virtual remanence originating from the lumped circuit models is derived for each rotor step. The validity of the proposed method is verified by comparing a two-dimensional and 3D FEM of skewed, non-skewed, overhang, and non-overhang machines.