Rotor vibration with auxiliary bearing contact in magnetic bearing systems Part 2: robust synchronous control for rotor position recovery

A number of conditions or events may produce rotor motion that involves contact with auxiliary bearings. Standard adaptive and closed-loop control strategies based on linear dynamics can cause instability when contact occurs, resulting in increased contact forces and vibration compared with the uncontrolled case. This paper introduces a method for robust control of synchronous vibration components that can maintain dynamic stability during interaction between the rotor and auxiliary bearings. The controllers are designed to minimize the severity and duration of contact and ensure that the rotor vibration returns to optimal levels, provided that sufficient control force capacity is available. Synthesis of controller gain matrices is based on a linear time-varying system model, which can be derived from either on-line identification routines or theoretical modelling and simulation. The controllers are tested experimentally on a flexible rotor system with magnetic bearings and are shown to restore rotor position control to optimal levels without further contact.