Advanced Cooling Methods for High-Speed Electrical Machines

Abstract

High-speed electrical machines are gaining increasing attention, as they enable higher power densities in several applications such as micromachining spindles and turbo compressors. This brings along an important challenge in thermal management due to the higher loss densities in the machine. Therefore, a careful thermal analysis is required along with the electromagnetic and mechanical considerations during the design phase of the machines. In this paper, different forced cooling options are compared for a slotless-type high-speed permanent-magnet machine. Fast, yet sufficiently accurate thermal models are derived for analyzing these cooling concepts. This enables their coupling with electromagnetic models and incorporation into the machine optimization procedure, which would not be feasible when using computationally very intensive methods such as three-dimensional finite element method or computational fluid dynamics. The developed thermal models are first verified on mechanically simplified stator designs (in which no rotor coupling is possible), and later on fully functional high-speed electrical machine prototypes. Using an integrated cooling method instead of a standard cooling jacket, the power density can be nearly doubled while keeping the maximum winding temperature below 80 °C, without altering the rotor or the stator core geometries.