Repetitive disturbance observer-based control for an active magnetic bearing system

Vibrations with time-varying frequencies significantly affect the performance of active magnetic bearing systems at high rotational speeds. It is well-known that these vibrations manifest as harmonic forces with frequencies synchronous to the rotor speed. It is important to attenuate these vibrations, as they may lead to system instability. This paper presents a hybrid control scheme comprising of an outer-loop controller and an inner-loop repetitive disturbance observer-based controller for the robust stabilization of a laboratory active magnetic bearing system while reducing the vibrations caused by the rotor mass-imbalance. The stability analysis of the presented hybrid control scheme (H_∞-RDOBC) is provided, and its effectiveness is verified via simulation studies and real-time experiments on a laboratory active magnetic bearing setup.