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

Doubly salient permanent magnet (DSPM) machines suffer from a large torque ripple due to unbalanced three phases, nonsinusoidal-phase back electromotive force, large cogging torque, etc. To suppress the torque ripple, this article proposes a new type of stator/rotor-pole number combinations. The number of stator poles is 18, while the number of rotor poles differs from the conventional counterpart (i.e., 12) by one. The DSPM machines with different stator/rotor-pole number combinations are globally optimized under the fixed copper loss and machine envelope. It shows that compared with the 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 densities remain almost the same. An 18/13 stator/rotor-pole DSPM machine is built and tested so as to experimentally verify such improvement.