A stator winding design with unequally-sized coils for adjusting air-gap space harmonic content of induction machines

In three-phase induction machines, the non-sinusoidal winding distribution normally causes space harmonics in the air-gap field, with negative impacts on stray-load losses and parasitic torques. An appropriate coil pitch choice is a traditional design strategy to improve the air-gap field waveform. In this paper an alternative technique is investigated based on using stator coils with unequal size. The proposed method does not affect the machine manufacturing process except for requiring two differently sized stator coil types. The effectiveness of the methodology is assessed both analytically and by mean of finite-element analysis, with a good accordance between the results independently obtained in the two ways.