Analysis and design of 6-phase fractional slot per pole per phase permanent magnet machines with low space harmonics

The paper is concerned with new winding configurations for 6-phase permanent magnet (PM) machines with 18-slot, 8-pole, that eliminates and/or reduces undesirable space harmonics in the stator mmf. The proposed configuration improves power/torque density and efficiency with a reduction in eddy current losses in the rotor permanent magnets and copper losses in end windings. To improve drive train availability for applications in electric vehicles, the paper proposes the design of 6-phase permanent magnet machine as two independent 3-phase windings. A number of possible phase shifts between two sets of 3-phase windings due to their slot-pole combination and winding configuration is investigated and the optimum phase shift is selected by analyzing the harmonic distributions and their effect on machine performance including the rotor eddy current losses. The machine design is optimized for a given set of specifications for electric vehicle (EV), under electrical, thermal and volumetric constraints.