Un-even winding turns in fractional-slot concentrated-winding PM machines

Fractional-slot concentrated-winding has a lot of advantages such as low cogging torque, short end winding and high power density, but the slot fill factor is relatively small with preformed windings when the slot number of machine is small. This paper explores un-even winding turns for double-layer FSCW machines to achieve higher slot fill factor on that situation. After suitable slot-pole combination is scanned, electromagnetic performances such as back-EMF and torque are compared with that of conventional FSCW topologies. It has been found that, for some slot-pole combinations, the FSCW machine with un-even winding turns has similar electromagnetic performance with conventional FSCW, but can achieve higher slot fill factor, which is a major concern with pre-formed windings for FSCW machine mass production. A FEM analysis of un-even winding FSCW machines is presented and design results of a sample machine are given.