Closed loop control of an electromagnetic stirrer in the continuous casting process

The continuous casting (CC) process is a crucial factor in determining quality of steel slabs, therefore directly affecting the scrap percentage and manufacturing costs. By braking or accelerating the liquid steel in the casting mould with the electromagnetic stirring (EMS) technique, the flow speed can remain in an optimal range in terms of slab quality. The EMS device employed in the CC of ArcelorMittal (AM) Ghent is controlled with an inferential control strategy. Here, the state of the caster is mapped to an assumed flow speed (which is not measured), revealing the need to brake or accelerate. By measuring the flow speed, using a sensor for the drag force, it was revealed that the flow is often too fast and drifts out of the optimal range, even if the machine state does not change. This paper presents the study performed to improve the current operation. A static model relating the electric current in the EMS device to the steel flow speed was derived, as well as a dynamic model. From the static model, a new inferential control strategy was proposed. Additionally, several dynamic closed loop controllers have been tested in simulations. Our study indicates that real plant implementation is feasible.