Winding factors and Joule losses of permanent magnet machines with concentrated windings

The torque to MMF ratio of a permanent magnet machine with concentrated windings is normally much lower than for the more traditionally used distributed windings. BLDC and AC machines with concentrated windings usually have a slot pitch of only 2/3 the length of the pole pitch, which results in a poor fundamental winding factor of 0,866. This can be compared to the ideal winding factor of one, which can easily be acquired using distributed windings. However, by choosing better combinations of the pole and slot numbers for a machine with concentrated windings, the winding factor can be substantially increased. Moreover, it is also possible to achieve low cogging torque without skewing, simply by selecting appropriate combinations. The presented theory includes both single- and double-layer configurations of concentrated windings. The theory is verified by using FEM analysis. This paper describes methods for designing high performance permanent magnet machines with concentrated windings.