Multipolar SPM machines for direct drive application: a general design approach

A closed-form, per-unit formulation for the design of surface mounted permanent magnet motors having high numbers of poles is hereby proposed. The analytical expression of machine inductances is presented, covering distributed and concentrated windings configurations. The paper addresses how the slot/pole combination, the geometric variables and the number of poles are related to average torque, the Joule loss and the power factor. The performance of distributed and concentrated windings machines is compared analytically, in normalized quantities. Last, the design approach is tested on four design examples, including all winding types and validated by finite element analysis.