Multivariable State Feedback Control of a 500 000-r/min Self-Bearing Permanent-Magnet Motor

The use of magnetic bearings in electrical drive systems enables very long lifetimes at highest speeds and the operation in high-purity or vacuum environments. The machine prototype presented in this paper overcomes several limitations of previously presented high-speed magnetically levitated electrical drive systems. The design features linear bearing characteristics, which enables applying linear state feedback control without linearization of bearing actuators. A multivariable rotor position control scheme is proposed and implemented on a signal processor. The implemented Kalman filter and the linear state feedback controller proved to perform well in practice, stabilizing the system over the design speed range of the machine with a single set of controller parameters. Closed-loop system transfer function measurements verify the presented system modeling and controller performance. Measurements of the machine spinning at 500 000 r/min verify the functionality of the overall system. To the authors´ knowledge, this is the highest speed achieved by magnetically levitated electrical drive systems so far.