Analysis of cogging torque and torque ripple according to unevenly magnetized permanent magnets pattern in PMSM

Abstract

This paper presents analysis of cogging torque and torque ripple according to unevenly magnetized magnet patterns in permanent magnet synchronous motor. In previous studies it has confirmed that non-uniformly magnetized permanent magnet causes unexpected increase of cogging torque and torque ripple because of slot harmonic components. However, these studies investigated insufficient number of irregular magnet patterns to accurately grasp the tendency about the effect of uneven magnetized magnet of rotor on torque ripple. In this study, various uneven magnet patterns were investigated using finite-element method and verified with the experimentation. As a result, it is proved that the unexpected increase of cogging torque and torque ripple can be reduced when the total sum of magnetic flux of N poles and S poles are equal, even if a few magnets are magnetized non-uniformly.