Suppression of periodic disturbances in the continuous casting process

In the continuous casting process, the steel level in the mold is controlled using a stopper rod as the flow control actuator and a level sensor. Various control strategies are used in order to reduce the mold level fluctuations which strongly affect the surface quality of the final product. Indeed, under certain casting conditions, the plant is often disturbed by periodic phenomena, in particular bulging or clogging-unclogging generating fluctuations over the free surface, which cannot be efficiently rejected by current controllers. This paper proposes a control architecture based on the introduction of compensation actions in the mold level regulation loop to cancel periodic disturbances occurring on the system. For that purpose, an observer is first designed which estimates disturbances signals. Due to the existence of a time delay within the system, these estimates are further predicted in order to be used as a feed-forward action acting in the control loop. The proposed method combining observer and feed-forward actions is finally validated in simulation, compared with the behavior without anticipative terms.