Comparative Study of Axial Length and Efficiency According to Coil Pitch of 2-Pole 6-Slot Ultra-High-Speed Machine

Abstract

The 2-pole 6-slot permanent magnet synchronous motor (PMSM) is an attractive option for ultra-high-speed (UHS) applications due to their high manufacturability and balanced magnetic force. UHS PMSM should be designed with short stack length and end coil height due to rotor dynamics issue. Also, due to its high frequency, it must be designed considering stator iron loss, rotor eddy current loss, and AC copper loss. With the same pole-slot combination, the performance varies greatly depending on the coil pitch, so this paper compared the size and efficiency of the 2-pole 6-slot UHS PMSM according to the coil pitch. For reasonable comparison, an optimal design was performed for each coil pitch, and to reduce computation time, the optimization was conducted in two stages: size minimization and efficiency maximization. It was confirmed that in terms of total axial length, 1-coil pitch was the shortest due to the advantage of short end coil height, even with the lowest winding factor. On the other hand, 2-coil pitch has good trade-off relationship in terms of efficiency and size.