Influence of step-air gap on line-start performance of u-shape single-phase permanent magnet motors

For the problem that the single-phase permanent magnet synchronous motor has no capability self-starting, the structure with a step-airgap is adopted. Under the effect of locating torque, there will be a phase angle existing between the rotor and stator magnetic field, so as to achieve a self-starter. By using 2D-FEM, it analyzed the influence of the step-airgap structure on armature field and permanent magnet field. The locating torques of motor in different rotor positions were determined from the analysis of the permanent magnet field by methods of virtual displacement, from which the initial phase angle of permanent magnet motor was obtained. On this basis, a series of curves that describe the relationships among the locating torque, phase angle and step-airgap structural parameters were obtained. At the same time, The curves testified that the rational step-airgap structural is beneficial to the self-starting permanent of magnet motor.