Reduction of space harmonics in induction machines incorporating rotor bar optimization through a coupled IPSO and 3-D FEA algorithm

An induction machine with skewed rotor bars has enhanced starting performance and reduced current harmonic distortion. In a conventional skewed induction machine (IM) modeling, the axial magnetic flux variation is usually ignored in machine performance analysis in spite of significant parameter variation in the axial direction. Furthermore, the selection of optimal skew angle is vital to keep the output torque constant, especially in electric vehicle applications. In this paper, a 7.5 hp IM with one slot pitch skew angle is considered as an initial model and space harmonic reduction has been investigated by considering axial variation of the air-gap flux density. An analytical model incorporating spatial harmonics due to slotting has been implemented in parallel with a 3-D FEA model towards improvements in skew angle and rotor bar geometry selection using improved swarm intelligence technique. The air gap flux density distortion and torque ripple due to space harmonic reduction for improved design are compared with that of the initial design.