Rotor dynamic experimental investigation of an ultra-high-speed permanent magnet synchronous motor supported on a three-pad bidirectional gas foil bearing

With a 10-kW, 120,000-r/min, ultra-high-speed permanent magnet synchronous motor taken as a prototype, experimental research is conducted on the rotor dynamic behaviours of a three-pad bidirectional gas foil bearing high-speed motor rotor system. Load-carrying properties of the three-pad bidirectional gas foil bearing are analysed, and natural frequencies of conical and parallel whirling modes of the elastically supported rotor are calculated based on an appropriate simplification to the stiffness and damping coefficients of the gas foil bearings. The prototype passes through a 90,000-r/min coast-down experiment. Experiments show that there are violent subsynchronous whirling motions that are evoked by the gas foil bearing–rotor system itself. The cause of shaft orbit drift is analysed, and the corresponding solution is put forward. The theoretical analysis and experimental results can offer a useful reference to the bearing–rotor system design of ultra-high-speed permanent magnet motors and its subsequent dynamic analysis.