Comparative Study Between Doubly Salient PM Machine with New Stator/Rotor-Pole Number Combination and Biased Flux PM Machine

This paper compares doubly salient permanent magnet (DSPM)machine having new stator/rotor-pole number combination with biased flux permanent magnet (BFPM)machine so as to verify its improvement in torque characteristics. In the DSPM machine, the stator/rotor-pole number combination is 18/13 rather than the conventional one (i.e. 18/12)to achieve balanced three phase, sinusoidal phase flux linkage and back electromotive force (back-EMF), small cogging torque, and low torque ripple. On the other hand, an 18/17-pole BFPM machine having the similar structure with the 18/13-pole DSPM machine is analyzed, which has the best torque performance among such machines with the same stator pole number. To further improve the average torque, the inner type flux focusing (FC)method is employed in the both DSPM and BFPM machines. Then both machines are globally optimized under the fixed copper loss and envelope size. The comparison shows that both machines have comparably small torque ripple while the 18/13-pole DSPM machine exhibits 35% higher torque density and 100% higher ratio of torque to PM volume. An 18/13-pole DSPM prototype machine is manufactured and tested in order to experimentally validate the simulation results.