Analysis and measurement of 3D torque and forces for permanent magnet motors with slotless windings

Slotless windings, skewed and rhombic, are widely used in industry. Beside the drive torque, possibly undesired transverse torques and forces are generated, which have not been analyzed previously. An analytical derivation of the torque and force components in all three directions is detailed in this paper for the skewed winding. It is shown that for some winding configurations alternating transverse torque components are generated, which may compromise stable operation in applications where for example magnetic or gas bearings are involved. Moreover the windings are analyzed with regard to a potential use as active magnetic radial bearings in high-speed applications. Finally, measurements are presented to verify the theoretical results.