Robust speed control for torsional vibration suppression of rolling mill drive system

In this paper, a novel robust torsional vibration suppression control scheme is proposed for the rolling mill drive system. We propose the torsional vibration suppression controller that consists of reduced order state feedback controller and PI controller; the motor speed and the observed torsional torque are fed back. Using the estimated mechanical parameters by off-line RLS (Recursive Least Square) algorithms, we design the speed controller for torsional vibration suppression and its gains are determined using the Kharitonov robust control theory. The Kharitonov robust control theory can obtain the robust stability with a specific stability margin and a damping limit. Even if the parameters are varied within some specific limit, it guarantees high performance of vibration suppression. The effectiveness and usefulness of the proposed schemes are verified with the simulation and the experimental results on the fully digitalized 5.5 kW rolling mill drive system.