Torque pulsation minimization in spoke-type interior permanent magnet motors with skewing and sinusoidal permanent magnet configurations

Interior permanent magnet motors (IPMMs) are increasingly popular in many applications for all power ranges due to their high torque density, high efficiency and wide operating range 1. In particular, the spoke-type IPMM has relatively high torque density benefiting from the permanent magnet (PM) flux concentration. However, it has drawbacks such as a serious distortion of airgap flux density distribution leading to distortion of the back-EMF and high torque pulsation (cogging torque and torque ripple), which is intolerable for high performance applications such as servo motors 2. Accordingly, various approaches have been proposed to reduce the torque pulsation 3-4. As one of the most widely used approach, skewing is effective to minimize cogging torque and improve back-EMF waveform, and is often used in surface-mounted PM motors. However, the conventional skewing method has a disadvantage of reducing the maximum available torque and yielding an unbalanced axial electromagnetic force 5.