The Avoidance of Saturation Limits in Magnetic Bearing Systems -2 During Transient Excitation

When a transient event, such as mass loss, occurs in a rotor/magnetic bearing system, optimal vibration control forces may exceed bearing capabilities. This will be inevitable when thc mass loss is sufficiently large and a conditionally unstable dynamic system could result if the bearing characteristics become non-linear. This paper provides a controller design procedure to suppress, where possible, bearing force demands below saturation levels whilst maintaining vibration control. It utilizes H, optimisation with appropriate input and output weightings. Simulation of transicnt behaviour following mass loss from a flexible rotor is used to demonstrate the avoidance of conditional instability. A compromise between transient control force and vibration levels was achieved.