Cogging torque reduction in surface mounted permanent magnet synchronous machine

This work examines minimization of cogging torque in surface mounted permanent magnet synchronous machines (SPMSM). Cogging torque arises due to magnetic interaction between slotted stator and permanent magnets at no load. Fractional slot winding machines have low value of cogging torque as dissimilar positions of the magnets increase the frequency of tooth harmonics. This work verifies two methods- pole shifting and proper selection of permanent magnet (PM) pole width-to reduce cogging torque in an 18-slot, 4-pole (fractional slot winding) SPMSM. These two methods reduce the harmonics and improve THD in back electromotive force (EMF). The proper selection of pole width also compensates the reduction in back EMF caused by pole shifting. Finite element method is used to verify the results.