Torque Pulsation Reduction in Fractional-Slot Concentrated-Windings IPM Motors by Lowering Sub-Harmonics

This paper proposes a method to reduce the torque pulsation of the three-phase fractional-slot concentrated-winding (FSCW) interior permanent magnet (IPM) motor by lowering sub-harmonics. The key principle of this method is the selection of an optimized six-layer winding with different numbers of conductors. Firstly, the interaction of stator-rotor magnetomotive force (MMF) which contributes to the torque pulsation is analyzed. Additionally, the relationship between sub-harmonics (1(st) sub-harmonic and 2(nd) sub-harmonic) and torque pulsation orders is revealed. Then, different numbers of conductors are adopted in coils to eliminate the 2(nd) sub-harmonic. Nevertheless, the 1(st) sub-harmonic increases in the two-layer and four-layer windings. Therefore, the optimized six-layer winding is employed to suppress the 1(st) sub-harmonic and ensure that the 2(nd) sub-harmonic is zero. Besides, there are almost no other harmonics except the main harmonic and slot harmonics in the proposed IPM motor. Hence, the torque pulsation can be greatly reduced even under different current angles. Furthermore, the principle for torque pulsation reduction by lowering sub-harmonics is revealed. The effectiveness of the proposed method is verified through the comparisons with finite element analysis and experimental test.