Reduction of Torque Ripple Caused by Slot Harmonics in FSCW Spoke-Type FPM Motors by Assisted Poles

Ferrite permanent magnet (FPM) has been employed in the spoke-type motors because of the low cost, stable supplement, and acceptable magnetic energy production. Especially, when the fractional slot concentrated winding (FSCW) is adopted, the torque ripple will be reduced. However, the torque ripple caused by the slot harmonics is difficult to be reduced in the FSCW FPM motors. Because the winding factors of the slot harmonics and the main harmonic are the same, the reduction of the slot harmonics from the stator or winding will lead to a significant torque loss. In this article, a new spoke-type rotor with assisted poles is proposed for the FSCW FPM motors. Due to these assisted poles, asymmetrical assisted poles can be realized along the circumferential direction to reduce the corresponding rotor magnetomotive forces (MMFs), which produce the torque ripple by interacting with the slot harmonics. The interaction of the harmonics that contribute to the torque ripple between the stator-MMF and rotor-MMF is first developed. Additionally, the relationship between the unequal angles and the orders of the torque ripple is obtained. Moreover, the principle to reduce the torque ripple in the FSCW spoke-type FPM motors is revealed. Finally, two prototypes are manufactured to evaluate the effectiveness of the theoretical analysis.