Improvement of mold-level control using fuzzy logic

Abstract

This paper reports on a feasibility study on an improvement of conventional mold-level control using fuzzy logic. Nowadays, for economic steel production, continuous casting is used. Of special interest for continuous casting is the mold, because in this part of the process the liquid steel will be fed to the mold. From the metallurgical point of view it is necessary to keep the mold-level constant, as large variations of the mold-level cause non-homogeneity in the product. Especially, an overflow of the mold (as well as an empty mold) has to be avoided, because the liquid steel overflows the working area or the bottom parts of the mold respectively. Besides an interruption to the production, high maintenance costs will be caused. Using an example of a slab-caster with varying mold geometry, this paper shows that in the case of disturbances an improvement on conventional control can be achieved by the use of fuzzy logic. The basic idea is the use of a parallel control structure with a complementary fuzzy logic controller. This provides the advantage that under normal operating conditions the conventional controller, in this case a PI controller, is still in operation, whilst in the case of a disturbance the fuzzy controller supports the conventional control. This leads to a much better disturbance control behaviour than without the fuzzy controller, with the result that, in contrast to conventional control, overflows can be avoided.