Analytical prediction of cogging torque in surface mounted permanent magnet motors

The contribution of this paper is to provide a simple but quite rigorous analytical method for computing the cogging torque in surface mounted permanent magnet synchronous machines. It relies on the fact that the magnetic energy variation due to the presence of a slot on the stator side of the airgap can be expressed on the basis of the airgap field the magnets should produce on the stator side of the airgap in absence of slotting, simply by taking the square of the value of this field at the position corresponding to the center of the slot and multiplying it by a coefficient k0 which depends on the square of the slot opening. The cogging torque formula which can be deduced from this expression of the energy variation due to a slot is simple and well suited for inclusion in an optimization process aiming at the minimization of this torque during the design of SMPM synchronous machines with equal tooth widths as well as of machines with unequal tooth widths.