Comparative Study of Various Slot Pitches for 2-Pole 6-Slot Ultra-high-Speed Permanent Magnet Synchronous Motors

The 2-pole 6-slot (2p6s) permanent magnet synchronous motor (PMSM) is an attractive option for ultra-high-speed (UHS) applications due to its excellent manufacturability and balanced magnetic force. UHS PMSMs should be designed with short stack lengths and end coil heights to address rotor dynamics issues. In addition, given their high frequency, these PMSMs should be designed considering stator iron loss, rotor eddy current loss, and ac copper loss. The performance of the same pole-slot combination varies significantly based on the slot pitch. Hence, we compared the size and efficiency of the 2p6s UHS PMSM based on the slot pitch. For a fair comparison, an optimal design was performed for each slot pitch. To reduce computation time, optimization was conducted in two stages: size minimization and efficiency maximization. It was confirmed that in terms of total axial length, the one-slot pitch UHS PMSM is the shortest due to the advantage of having a short-end coil height, even with the lowest winding factor and largest stack length. Furthermore, it was determined that the two-slot pitch UHS PMSM offers an excellent trade-off between efficiency and size.