Comparative Analysis of AC losses with round magnet wire and Litz wire winding of a High – Speed PM Machine

The growing trend of high speed, high power density machines for applications such as EVs, aerospace and machine tools demand these machines to work at higher electrical frequencies. Meanwhile, increasing the fundamental frequency leads to pronounced parasitic effects such as skin and proximity effects, which could induce considerable circulating current in stator windings. The additional winding loss due to these effects has generally made copper loss the dominant part of overall power loss in a high speed, high power density machine. This paper presents an in-depth investigation into the losses in the winding of a high-speed PM machine based on numerical FEA and compares the losses. Through loss comparison of various winding topologies using straight magnet wires along with Litz wire at high frequencies, it is found that transposition between coil turns which belong to the upper and lower coil sides can significantly reduce the AC copper loss.