3-D Effects of Rotor Step-Skews in Permanent Magnet-Assisted Synchronous Reluctance Machines

This paper focuses on the 3-D effects associated with rotor step-skews performed in permanent magnet-assisted synchronous reluctance machines (PMA SynRMs). It analyzes and quantifies these effects via comparisons between 2-D and 3-D finite-element analyses (FEA) of skewed and unskewed machines. The 3-D phenomena manifested in the skewed PMA SynRM are identified into end-effects and axial interactions between skewed steps, and their influence on its electromagnetic performance is examined under load and no-load conditions. This paper exemplifies the significance of the skew-associated 3-D effects, which can result in considerable decrease of the back electromotive force and a substantially increased electromagnetic torque ripple. It, thereby, highlights the inability of the typically employed multislice 2-D FEA or other existing 2-D-based modeling techniques in taking their influence into account. The validity of the findings is experimentally verified with measurements acquired from a prototype PMA SynRM using skewed and unskewed shafts in the rotor.