A Model-Based Predictive Controller of the Level of Steel in the Mold with Disturbances Using a Repetitive Structure

Rogério P Do A Pereira,Marco A De S L Cuadros,Ricardo O De Freitas,Gustavo M De Almeida,Carlos T Valadão,Teodiano Bastos-Filho,José L Felix Salles

doi:10.3390/met11091458

Rogério P Do A Pereira, Marco A De S L Cuadros + Show 5 more

Open Access

https://doi.org/10.3390/met11091458

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Abstract

Keeping the level of steel in the mold of the continuous casting process constant is fundamental for the quality of the steel produced and, consequently, its commercial value. It is challenging, considering the several disturbances that cause undesired variations in the mold level. The aim of this paper is to apply a repetitive structure composed of two controllers, a generalized predictive controller (GPC) and a repetitive GPC (R-GPC) with constraints to mitigate the bulging and clogging/unclogging disturbances and the casting speed variation in the mold level of the process. The R-GPC controller has the same characteristics as the GPC, such as performance, robustness to disturbances, and insertion of constraints, and its advantage is the elimination of periodic disturbances. The repetitive structure will be implemented with a robustness filter and tuned by a genetic algorithm (GA). The controller tests are performed by simulations of a nonlinear mathematical model of the mold level, validated using real data from the steel industry. The proposed controller reduces the bulging disturbance amplitude by 98.5% and at 25% of the frequency of reversions in the valve. Consequently, the proposed controller allows an increase in the valve life span, a reduction in maintenance costs, and quality improvement in the steel slab.

Highlights

Continuous casting is a process in which molten metal is solidified in the form of billets, blocks, or plates for later lamination
The repetitive structure with constraints will be applied in a mold level simulator that represents a real plant when it is affected by the bulging, clogging/unclogging disturbances and variations in casting speed
This work proposed a repetitive structure composed of two controllers, the generalized predictive controller (GPC) and the repetitive GPC (R-GPC), to control the mold level, which is subject to bulging and clogging/unclogging disturbances, and variations in the speed of the continuous casting process

Summary

Introduction

Continuous casting is a process in which molten metal is solidified in the form of billets, blocks, or plates for later lamination. In steel slab production, the liquid steel comes from the ladle as an outcome of stages prior to the continuous casting process. The tundish receives this liquid steel and maintains its supply for the machine during the exchange of ladles, directing the flow of steel into the mold, where the first solidification is promoted on the surface of the slab. During the path between the steel rolls of segments, the cooling process continues with a spray of water and air, causing the solidified layer to thicken until it is time for complete extraction from the machine when the steel is completely solidified.

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