Surface Permanent Magnet (SPM) machines with slotless stator design are used is some applications where torque pulsations and/or the additional losses due to slotting effects need to be eliminated. These machines have a geometric structure allowing for an accurate analytical solution for the magnetic fields, which is desirable especially for optimization purposes. This paper derives a compact but exact analytical formula for the load torque computation in slotless SPM machines. The formula has the advantage of well highlighting the dependence of the load torque from machine construction details. It can be therefore useful in the design and dimensioning stage as a fast alternative to time-consuming Finite Element (FE) analysis.
