Influence of flux focusing on electromagnetic torque of novel biased flux PM machines

A novel biased flux permanent magnet (PM) machine (BFPMM) with doubly salient structure and PMs located in the stator back-iron is investigated in this paper. The stator is constituted by T-shaped laminated segments between which are placed circumferentially magnetized magnets of alternate polarity, and a concentrated winding is wound around each stator pole. The rotor has salient structure which is similar to that in a switched reluctance machine (SRM), whilst the choice of its pole number is flexible and can be chosen to be any integer except equal to the phase number and its multiples. When the number of stator and rotor poles differed by one, 6-stator pole BFPMM exhibits bipolar phase flux-linkage and sinusoidal phase back-EMF. Three types of flux focusing are proposed to increase the slot area and improve the torque performance. The results show that they can produce higher phase flux-linkage and back-EMF as well as larger torque capability at rated copper loss.