Investigation of Efficiency Enhancement of an Ultra-High-Speed Bearingless Motor at 100,000 r/min by High Switching Frequency Using SiC-MOSFET

This paper introduces the operational characteristics of an ultra-high-speed bearingless motor with 2-pole concentrated motor windings and 4-pole concentrated suspension windings. Experiments with a prototype machine indicate that iron loss is the largest component of losses in the proposed bearingless motor. Therefore, in order to reduce the iron loss, comparison of the experimental results and the 3D-FEM results is discussed. As a result, because it is turned out that iron loss of the switching frequency component accounts for a large proportion in total iron loss, a method of enhancing efficiency of the proposed bearingless motor by means of high switching frequency using SiC-MOSFET is examined. The experimental results with the examined method show that the prototype machine can attain the high efficiency of 94.3% at rated operation of 1.70 kW and 100,000 r/min in spite of including suspension input power for magnetic levitation. In addition, operational characteristics comparison of the bearingless motor at switching frequency of 40 kHz, 80 kHz and 120 kHz is discussed in detail.