COMPARATIVE ANALYSIS OF MULTIVARIABLE ADVANCED CONTROLS APPLIED TO THE HOT ROLLING MILL INTERSTAND PROCESS

摘要

Final hot rolling of steel strip is done in afinishing mill which generally consists in seven horizontalstands in tandem. In each interstand, the strip is deflected by alooper made of an idle or motorised roll located at the end ofan oscillating arm controlled by hydraulic or electromecanicdevice. The basic process of the finishing interstand is then ahighly coupled and unbalanced multivariable system, the twoactuators being the looper in interstand and the main motorsdriving the rolls of the upstream rolling stand, the twovariables to be controlled being the looper angle and strip tension.Strict, simultaneous control of these two parameters requiresadvanced controls capable of meeting the following requirements:? sufficient performances in terms of disturbance rejection andset point tracking,? reduction of mutual interactions between the looper angle and strip tension,? robustness with respect to the overall uncertainties of the process,? working of the actuators within acceptable thresholds.Consequently, this paper proposes a comparative synthesis bysimulation on a specific physical process of differentmultivariable control structures.