Development of a Slotless Permanent Magnet Motor with Two-Layer Toroidal Winding for Minimization of Torque Ripple

This study presents a novel slotless permanent magnet (PM) motor with two-layer toroidal winding to minimize the torque ripple, which can be applied to, for instance, servo-motor system with precise positioning control. Two-layer toroidal winding arrangement with 18 segments is employed to drive two-pole surface-mounted PM rotor. The optimal ratio of the number of winding conductors is theoretically derived to eliminate 5th, 7th, 11th, and 13th spatial harmonic components in the stator magneto-motive force distribution. The motor torque was calculated by finite-element-method, and the calculation results demonstrated that the proposed two-layer toroidal winding arrangement had a reduced torque ripple of 0.12 %. The prototype motor was built and tested. The measured back-electro-motive-force has 0.9 % total harmonic distortion.