Design of a super-high speed permanent magnet synchronous motor for cryogenic applications

This paper gives the design and simulation of a permanent magnet synchronous motor (PMSM) for a super-high speed centrifugal compressor drive application. The PMSM has an output power of 2000 W at 200,000 rpm with 28 V dc power supply. It is designed for operation at a cryogenic temperature of 77 K. The designed PMSM is a 2-pole, 3-phase slotless structure. The permanent magnet is centrally located inside the hollow shaft. Multi-strand twisted Litz-wire is used to reduce eddy current loss in the winding. The criteria of selecting materials for the super-high speed and cryogenic application are presented. Possible structures of the rotor and stator are considered and simulated using finite element method (FEM). Mechanical stress simulation and rotor dynamic issues are also considered. The connections of low pass filters to reduce switching harmonics of pulse-width modulation (PWM) and to reduce circulating current are also discussed. The first prototype has been fabricated and tested at room temperature. Projected total efficiency of the motor is over 90%