Effects of manufacturing tolerances of permanent magnets in fractional slot permanent magnet synchronous machines

Abstract

The fractional slot permanent magnet synchronous machines are well-known for their low torque ripple. However, in mass-production machines, not all the permanent magnets are identical due to the manufacturing tolerances and new torque harmonics could appear. In addition, the magnetic field is modified and unbalanced magnetic pull (UMP) could happen. Apart from that it is important to study the effect on vibrations since the magnetic field is no longer ideal. So, here, a study of the effect of unevenly magnetised permanent magnet distribution on torque ripples, unbalance magnetic pull, and vibrations is proposed. Apart from that, the tolerance grade sensitivity is studied. Finally, experimental tests show good agreement with finite element analysis.