Influence of Design Parameters on Performance of PM AC Motors with Fractional-Slot Windings

This paper studies the influence of the design parameters on electromagnetic performance of permanent magnet ac motors with an exterior rotor having surface mounted magnet poles, and a stator having fractional slot concentrated windings. The study focuses on the quality of the back emf in terms of magnitudes and total harmonic distortion, and the torques developed in the motor. The electromagnetic performance of permanent magnet ac motors with various slot-pole combinations are analyzed by both finite element methods and analytical modelling. The influences of key design parameters are also examined in details, such as the slot opening, pole-arc to pole-pitch ratio, and the tooth tip height in addition to the slot-pole combinations. The method employed in this paper is generally applicable to the design and analysis of permanent magnet ac motors with concentrated stator windings, one of the multi-pole motor configurations used for direct drive wheels in electrical vehicles and autonomous robots.