Active magnetic bearings are increasingly used for turbo-molecular pumps, machine tool spindles and canned motor pumps. These bearings are inherently unstable and require closed-loop controllers with position feedback. Several instances of implementing gain-scheduled controllers have been reported in the literature. In most of these works, the gain scheduling is done based on the operating RPM of the rotor. In this work, the gain scheduled control is implemented based on the commanded reference position in addition to the operating speed of the levitating rotor. Such a gain scheduled control is helpful in applications such as machine tool spindles where the reference position of the rotor is not at the midpoint of the air gap but over a range of values within the air gap.
By taking into account the change in characteristics of the AMB at other references and implementing multiple Linearised controllers, we can meet the design specifications at these multiple reference points. The design of the multiple Linearised controllers is performed using plant models obtained from a plant model identification study. The gain-scheduled controller is then implemented to show the performance improvement compared to a single mid-point controller.