Single and double layer windings in fractional slot-per-pole PM machines - effects on motor performance

This paper discusses the effects of fractional slots per pole in brushless permanent magnet motors. Example machines with 12, 16 and 20 pole are used to highlight their operation when using fractional slot windings and the performance is investigated in terms of winding MMF harmonic and torque production. 2D finite element analysis is used to simulate the machines in order to carry out the study. Torque ripple, cogging torque and back-EMF waveforms are all assessed for the example machines. The variation in the torque-speed operating areas is investigated to assess the operating ranges of the different arrangements.