Performance Analysis of Interior Permanent Magnet Motor Using Overlapping Windings With Fractional Ratio of Slot to Pole Pair

Conventional concentrated windings with fractional-slot per-pole per-phase (SPP) are widely used to reduce the cogging torque and ripple torque of interior permanent magnet (IPM) machines. However, the rich magnetic motive force (MMF) harmonics of the fractional SPP concentrated winding (FSCW) will result in high rotor losses. This paper proposes a new overlapping winding with fractional slot per-pole-pair (SP), which can greatly reduce the pulsating torque with lower winding harmonics. First, the principle of the proposed winding configuration is analyzed with respect to the cogging effect and the stator MMF. Then, the electromagnetic performances of the new fractional SP windings are compared to that of integer SPP windings, FSCWs and odd SP windings in terms of airgap flux density, back electromotive force, cogging torque, average torque, torque ripple, and losses. It is found that the IPM machine with the proposed winding configuration has the lowest cogging torque and ripple torque, and its winding MMF harmonics are significantly smaller than that of the IPM machine with FSCWs.