Increasing the external damping of a flexible rotor by periodic control

The influence of a periodic open-loop control operated in parallel to an existing closed-loop PID control is investigated on a rotor system supported by two radial active magnetic bearings. The transient behaviour of the rotor is studied numerically and first experimental results are shown to demonstrate the applicability of the method. It is highlighted that by tuning the periodic control properly it is possible to amplify artificially the external damping of the rotor system. This concept allows increasing the total external damping well beyond the stability margin of the closed-loop control cycle.