QFT for the Design of Active Magnetic Bearings Control Systems

The paper describes the application of Quantitative Feedback Theory (QFT) to the control of active magnetic bearing systems (AMB’s). In order to provide a practical focus to the study, the magnetic bearing system of a highspeed energy storage flywheel is considered. QFT templates are employed to specify multi-objective performance constraints for the closed-loop AMB systems to accommodate stability robustness, static and dynamic stiffness requirements, closed-loop bandwidth criterion, the finite power capabilities of the electronic amplifiers, and disturbance rejection properties. Subsequently, the design of various compensation schemes, based on loop-shaping, which satisfy the QFT performance boundaries, and hence, impose the desired attributes on the closed-loop system, is described. Experimental realisation of the resulting compensators to control the AMB’s which support the flywheel rim validate the theoretically predicted attributes of the closed-loop system. Thus, QFT is shown to be a very effective methodology for the design of controllers for active magnetic bearing systems.