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

A closed-form, per-unit formulation is proposed, for the design of surface mounted permanent magnet motors with high number of poles. The model evaluates the shear stress, the power factor and the specific Joule loss as the indicators of the machine performance, and demonstrates that this is determined by the correct choice of a very limited set of key-geometrical parameters. The design criteria are described analytically and then applied to example designs, FEA validated. Distributed- and concentrated-winding configurations are considered. The conclusions of the paper are consistent with the literature and aim to give a roadmap for designers of PM machines in modern applications, such as wind power synchronous generators.