Analytical calculation of the no-load flux density in the stator core of slotless SPM machines

Slotless Surface Permanent Magnet (SPM) machines are used is some applications where the torque ripple and / or the additional losses due to slotting 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 an analytical formula for the flux density in the stator core of slotless SPM machines during no-load operation. The derived formula is assessed by comparison with Finite Element (FE) analysis. It is shown how it can be used for the computation of no-load core losses including rotational eddy current effects. The method proposed can be naturally extended to determine the core field due to armature reaction as well.