Robust control of a magnetic-bearing flywheel using dynamical compensators

This paper considers the robust control of a current-controlled magnetic bearing with a pair of opposing electromagnets and a rigid rotor. A first-order dynamical compensator which uses only position feedback information is applied for control. The dynamical compensator design is based on a linearized one-dimensional second-order linear model, which is treated as an interval system in order to cope with parameter uncertainties. Through robust stability analysis, a parameterization of all the first-order robust stabilizing dynamical compensators for the interval magnetic-bearing system is first obtained. Then, by appropriately selecting the free parameters in the robust stabilizing controller, the H-two norm of the disturbance-output transfer function is made arbitrarily small over the system parameter intervals, and the H-infinity norm of the output-input transfer function is made arbitrarily close to a lower bound. The proposed approach is applied to control a flywheel supported by active magnetic bearings. Simulation and experimental results show that this approach is simple, effective and very robust.