Bearingless Generator Design and Optimization for High-Speed Applications

High-speed generators are gaining popularity due to their compact design, high power density, and high efficiency. However, the lifetime and reliability of these generators are often restricted by mechanical bearings. Bearingless generators could offer an alternate solution where the rotor is levitated using suspension forces created by magnetic fields within the electric machine. By eliminating mechanical wear, bearingless machines can operate reliably at high speeds, potentially increasing the power density of the generator. The objective of this paper is to investigate the design of bearingless generators for high-speed applications. The paper reviews the current state of research on high-speed generators, including design requirements and considerations, and uses these findings to propose a bearingless generator system topology. An optimization framework is established to explore the design space for a rated power of 50 kW at the rated speed of 25 krpm and 100 krpm. Compelling designs are found to have high efficiency ($\gt 97$%), high power factor ($\gt$ 0.9), and low back-emf total harmonic distortion (THD) ($\lt 5$%) while simultaneously levitating the rotor. This investigation finds that bearingless machines have the potential to be a high-performance solution for high-speed generator applications.