Multivariable state feedback control of a 500 000 rpm self-bearing motor

The use of magnetic bearings in electrical drive systems enable 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. Linear bearing characteristics result from the slotless design, which enables applying linear state feedback control without linearization of bearing actuators. A multivariable rotor position control scheme is proposed and its controller performance is analyzed in details. The implemented control scheme proved to perform well in practice, stabilizing the system over the design speed range of the motor with a single set of controller parameters. Measurements of the motor spinning at 500000 revolutions per minute (rpm) 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.