Synthesis and implementation of gain-scheduling and LPV controllers for an AMB system

Active Magnetic Bearing (AMB) spindles are often subject to synchronous vibrations due to mass-imbalances. The frequency of these vibrations is equal to the rotational speed of the spindle. Conventionally these vibrations are viewed as sinusoidal disturbances acting on the outputs, and an LTI feedback controller is designed that contains a notch in the loop. This method is useful when the operating/rotational speed of the spindle is accurately known in advance. When the disturbance rejection is required at multiple operating points, the performance offered by a single LTI controller is insufficient. In this paper, we discuss the application of LPV control and gain scheduling via H∞H∞ controllers to an experimental AMB setup, for disturbance rejection over a range of operating speeds. We synthesize 3 LPV controllers and gain-schedule between 24 H∞H∞ controllers. All the synthesized controllers are unstable and hence we use a Youla parametrization based switching method to implement the controllers on a dSPACE DS1103 processor.