Improved Stator/Rotor-Pole Number Combinations for Torque Ripple Reduction in Doubly Salient PM Machines

Doubly salient permanent magnet (DSPM) machines suffer from large torque ripple due to unbalanced three phase, non-sinusoidal phase back-electromotive force (back-EMF), and large cogging torque etc. To reduce the torque ripple, this paper proposes a novel type of stator and rotor pole combinations. The stator pole number is 18, while the rotor pole number differs from the conventional rotor pole number (i.e. 12) by one. The DSPM machines with different stator and rotor pole combinations are globally optimized under the fixed copper loss and machine size. It shows that compared with 18/12 stator/rotor-pole DSPM machine, the torque ripples of 18/11-and 18/13 stator/rotor-pole DSPM machines are reduced significantly, while their torque density remains almost the same. An 18/13 stator/rotor-pole DSPM machine is built and tested so as to experimentally verify such improvement.