Simple nonlinear magnetic analysis for three-phase hybrid stepping motors

Hybrid stepping motors (HBM) are one of the candidates for direct drive motors and will be more attractive from the standpoints of higher torque capacity and efficiency by combining the rare-earth magnets. However, in general, since HEM have a great number of small-teeth on the stator and rotor surface, the magnetic saturation in the teeth becomes severe with increasing flux-density in the air gap. In addition, the magnetic nonlinearity makes the design of the motor more difficult. Although 3D-FEM is one of the solutions for the magnetic nonlinear analysis of HEM, a large amount of computation time is necessary. This paper presents a simple nonlinear magnetic analysis of HEM for an assistant design tool of 3D-FEM. The equivalent magnetic circuit of the motor used in the proposed magnetic analysis is composed of the air gap permeance model between the stator and the rotor teeth which includes the saturable permeance tips in the teeth for considering the local saturation. The validity of the proposed analysis has been verified through the comparisons between the measured and the calculated electric parameters of 400 W test motor which uses a Nd-Fe-B magnet having a BH-product of 255 kJ/m³