Asymmetric Design of Consequent Pole to Reduce Torque Ripple

Abstract

Consequent pole permanent magnet synchronous motors (CP-PMSMs) have received attention because they can reduce the amount of permanent magnets used. Due to structural features, the magnetic flux of the air gap is imbalanced. Furthermore, torque ripple increases due to even harmonics of back electromotive force (back EMF). In this article, we propose an asymmetric design method to reduce torque ripple and magnet usage in consequent pole (CP) surface permanent magnet synchronous motor (SPMSM). First, the iron and magnet pole areas are selected asymmetrically to increase torque and reduce torque ripple. Second, the N pole of the CP-SPMSM (CP-Npole) and the S pole of the CP-SPMSM (CP-Spole) are combined in the axial direction to reduce the even harmonics of back EMF. An air gap is inserted between the two CP-SPMSMs to reduce axial leakage caused by the combination of opposing poles. Then, the location and axis length of the iron pole are designed asymmetrically. Torque ripple is further reduced by reducing the harmonics multiple of 6 of the back EMF. Finally, we compare the electromagnetic characteristics of SPMSM and CP-Npole with the proposed model. The proposed model reduces torque ripple and increases torque per permanent magnet usage. We performed the finite-element analysis in 3-D to analyze all models’ axial electromagnetic characteristics.