Three phase tooth-concentrated multiple-layer fractional windings with low space harmonic content

The possibility of obtaining lower space harmonic content for the fractional-slot, tooth-concentrated windings by multiplying the number of coils, leading to bigger number of layers in the armature slots is presented. By using multiple layer windings it is possible to reduce or even to cancel some space sub-harmonics having as final result lower eddy current losses induced by the armature reaction in the iron structure of the rotor. The general method of doubling (or trebling) the winding and relatively shifting by one (or more) slots is presented in the paper. Two examples of three phase concentrated windings are presented and analyzed as primitive windings, 12 slots/10poles and 9 slots/8 poles. In the first case the only existing space sub-harmonic is reduced firstly from 35.9% (from fundamental wave) to 9.6% and finally it is canceled by using different number of turns per coils. In the second case the two existing sub-harmonics are reduced and balanced by using the developed method.