Torque investigation of fractional-slot permanent magnet machines with different winding topology and stator structures

For fractional-slot PM machines with nonoverlapping windings, the influence of winding topology and the stator structure on torque performances are investigated in this paper. With the help of frozen permeability method, the on-load torque is separated into PM, armature current component and cogging torque, respectively. The major contribution of average torque and the causes of on-load torque ripple are identified by analyzing these components. Since torque performances are closely related to the armature reaction field, the predominant factors, viz. winding arrangement, current amplitude and stator structure, are investigated. It can be concluded that the local saturation of stator yoke due to the interaction between PM and armature reaction affects not only the average torque value but also the torque ripple.