Relation between magnetic properties of stator core and cogging torque in 8-pole 12-slot spm synchronous motors

Abstract

This paper discusses the influence of the magnetic properties of the stator core on cogging torque in 8-pole 12-slot surface-mounted permanent-magnet synchronous motors from the perspective of magnetic energy. In the finite element analyses of magnetic fields with modeled stator BH curves, cogging torque decreases drastically when the shape of magnets is changed from an arc to a semi-cylindrical structure. The influence of the stator BH curve on cogging torque is dominant in the low-cogging-torque motor with semi-cylindrical magnets. This is because magnetic energies in the gap and the magnets cancel each other and the magnetic energy in the stator core is dominant in the low-cogging-torque motor. Low maximum permeability and low magnetizing force in a high-B region are preferable for stator magnetic properties to reduce cogging torque. This is explained by the behavior of harmonics in the stator magnetic energy variation. The influences of steel grade, compressive stress, and punching in the stator core on cogging torque analyses are consistent with the results for the modeled BH curves. Low grade electrical steel sheets, high compressive stress, and magnetic annealing are effective to reduce cogging torque in the described motor design.