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 winding configurations. This paper addresses how the slot/pole combination, the geometric variables, and the number of poles are related to the average torque, the Joule loss, and the power factor. The performance of distributed and concentrated winding machines is analytically compared, in normalized quantities. Last, the design approach is tested on four design examples, including all winding types, and is validated by finite-element analysis.