Design of an E-core flux-switching permanent magnet machine with large air-gap

A 6/8 E-core flux-switching permanent magnet machine with large air-gap (δ=3 mm) for a medium speed application (n=6000 rpm) is presented. General aspects of machine design arising from the large air-gap length of the machine are discussed using 2D-Finite Element Analysis. It is found that the design rules for conventional or even alternate FSPM machines can no longer be applied when a large air-gap is present. Particularly the choice of rotor poles is investigated to improve the torque capability of the FSPM machine in detail. Within the machine design it is necessary to reduce the number of rotor poles which is also beneficial for the reduction of losses at increased rotor speeds. Moreover, the height of the permanent magnets in the stator also need to be enlarged due to the large air-gap machines to prevent a direct short circuit of the permanent magnet flux in the air-gap. Additionally, the influence of rotor skewing on the torque variation is briefly discussed.