Analysis of coil pitch in induction machines for electric vehicle applications

This study investigates the influence of stator coil pitch on the electromagnetic performance of squirrel-cage induction machine (IM) with emphasis on the flux-weakening (FW) capability for electric vehicle applications. Three different winding topologies, obtained by changing the coil pitch, namely integer-slot distributed winding (ISDW), integer-slot concentrated winding, and fractional-slot concentrated winding (FSCW), are studied. Their merits and demerits are revealed by comparing their performances characteristics, including winding harmonic index, total axial length, average torque, torque ripple, power losses, efficiency, and FW capability. It is revealed that due to the very high Magnetomotive force (MMF) harmonics induced in the bar current, the bar copper loss of the IM with FSCW is significant. It is also revealed that the parasitic effects of the double-layer winding configurations are lower than those of the single-layer (SL) winding configurations. It is also demonstrated that for the slot/pole/phase combinations lower than two q ≤ 2, the higher the coil pitch, the lower the parasitic effects and the higher the efficiency. Moreover, it is found that the combinations q ≥ 2, especially those having longer coil pitch and higher stator slot number, and the SL combinations offer better FW capability. Finally, the Finite-element analysis (FEA) results of IM with long-pitch ISDWs are validated by experimental measurements.