Combined Radial-Axial Magnetic Bearing for a 1 kW, 500,000 rpm Permanent Magnet Machine

Ultra-high-speed and high-power-density drives are attracting much interest in today´s industry. For instance, there are several investigations into mesoscale gas turbine generator systems and turbocompressors for fuel cells. In all ultra-high-speed machinery the bearing is a key technology. Therefore, this paper focuses on the design of a 500,000 rpm active magnetic bearing suitable for use in a 1 kW PM machine to complete an ultra-high-speed electrical drive system. The design procedure selects the suitable magnetic bearing type to keep the system compact and small. The electromagnetic characteristics are determined, the results for the rotor dynamic analysis are presented and the air friction losses caused by the high frequency operation are evaluated. The final design is a combined radial-axial magnetic bearing with a volume of 50 cm3.