Analytical calculation of air-gap armature reaction field including slotting effects in fractional-slot concentrated-coil SPM multiphase machines

Abstract

Fractional-slot concentrated-coil electric machines are often used especially in those applications where a number of rotor poles close to the number of stator slots is required. A major criticality of such machines is the occurrence of large air-gap field harmonics due to winding distribution and to slotting effects. Predicting such harmonics analytically with adequate accuracy is a good way to significantly speed-up subsequent investigations concerning the rotor effects of the field harmonics in terms of rotor losses. This paper proposes different analytical formulations for this purpose, covering the case of a generic number of stator phases and differing by how slotting effects are taken into account. The various approaches proposed are evaluated by comparing analytical results with FE analysis computations on a sample machine geometries.