Variable-structure control of casting processes

The paper is concerned with the problem of regulating the molten metal level in the mold of a continuous casting plant despite the continual perturbations caused by mold shaking and the occasional perturbations due to the sudden uncloggings of the nozzle through which the liquid is poured into the mold. To deal with both kinds of perturbations, two distinct controllers are used and suitably activated depending on the operating conditions. It is demonstrated that a controller realization obtained from any time-varying convex combination of two switching-stable controller realizations ensures stability, too. Numerical simulations show that the adopted stability-preserving control policies compare favourably with alternative techniques suggested in the literature to the same purpose.