Design criteria for high-efficiency SPM synchronous motors

This paper deals with the design criteria for a high-efficiency permanent magnet synchronous motor. The goal is not pursued by a trivial reduction of the electric and magnetic loadings (which decrease motor losses) but optimizing a set of motor design variables, without increasing the overall dimensions, which are typically imposed as design constraints. The effect of the number of slots and of the inner-to-outer diameter ratio on motor losses is investigated. The possibility of designing a stator with a tooth length lower than the total core length, using soft magnetic composites, is studied. Finally, a criterion is proposed to evaluate the convenience of using a nonoverlapping winding. An analytical approach is adopted so as to allows the obtained results to be useful for a wide variety of permanent magnet machines.