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.
The quantification of stray load losses such as circulating-current loss in armature windings and in-plane eddycurrent loss in electrical steel sheets is important for developing rotating machines with high efficiency. The circulatingcurrent loss in parallel-connected armature windings is analyzed by using the two-dimensional finite element method. We investigate the losses caused by the in-plane eddy-current in the stator cores of permanent-magnet synchronous machines by using the three-dimensional finite element method. The influences of the coil-end structure, skew structure, and carrier harmonics of a pulse-width-modulated inverter on the in-plane eddy-current loss in the stator core are described. The accuracy of the analyses is confirmed through comparison with experimental results.
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