Analysis and Measurement of Three-Dimensional Torque and Forces for Slotless Permanent-Magnet Motors

Slotless windings, both skewed and rhombic, are widely used in industry. In addition to the drive torque, possibly undesirable transverse torques and forces are generated. An analytical derivation of the torque and force components in all three directions is detailed in this paper for the skewed and the rhombic windings. 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. Finite-element method results, which enable the transverse torque for various winding geometries to be quantified, are also included. Finally, the theoretical results are verified by measurements.