On the Speed Limits of Permanent-Magnet Machines

Permanent-magnet (PM) machines are considered the most suitable machine type for very high speed applications. Still, due to the growing demand for the ever higher rotational speeds, PM machines are approaching their limits. The focus of this paper is the different factors that lie behind the inherent speed limitations of PM machines. The limits-thermal, elastic, and rotor dynamical-are defined, classified, and correlated to basic machine parameters.