Interior Permanent Magnet Motor With Novel Opposing Unequal Magnetic Poles for Torque Ripple and Electromagnetic Vibration Suppression

Interior permanent magnet (PM) motors have been widely used in traction systems because of their advantages of high efficiency, compactness, and high power density. However, due to the differences between the d- and q-axes inductances in interior PM motors, the electromagnetic vibration caused by complex electromagnetic forces is relatively intense. The existing methods for the optimal design of rotor structures are usually susceptible to axial length constraints and may introduce unbalanced magnetic pull. In this article, a novel rotor structure with opposing unequal magnetic poles to suppress torque ripple and electromagnetic vibration for traction motors is proposed. The proposed rotor structure is divided into two segments and staggered by 90°. In each segment, the volume and size of all the magnets remain identical, while the intersection angle between two magnets of the radially symmetrical V-shaped pole is adjusted, resulting in different pole arc widths compared to other poles. Meanwhile, the symmetrical magnetic poles can avoid the radial unbalanced magnetic pull. Afterward, the radial electromagnetic force is systematically analyzed, and the electromagnetic performances are compared with the original motor and the rotor step-skewing motor. Finally, the three motors are prototyped, and the results show that the proposed motor can effectively reduce torque ripple and suppress the 0th-order and 8th-order electromagnetic vibration.