Reseach on Generalized Predictive Control in Hydraulic AGC System of Cold Rolling Mill

Abstract

Because request to quality of cold rolling sheet strip is higher and higher, the hydraulic AGC (Automatic Gauge Control) system has been a requisite means for improving quality of cold strip’s finished products. But PID control strategy, being comprehensively used in the locale, is difficult to satisfy request of improving control precision of hydraulic AGC. Generalized predictive control (GPC) is one of predictive control theories. It needs few parameters, and adopts strategies of multi-step prediction, receding-horizon optimization and feedback correction, which has good tracking characteristic and reduces on-line calculations of control algorithm. So it’s a kind of indispensable and practical strategy for exploring the application method of generalized predictive control. First, the direct algorithm of generalized predictive control was applied in the electro-hydraulic servo system of cold rolling mill, which adopted the stochastic gradient estimate algorithm to estimate parameters of controller on-line. It avoided on-line solving the Diophantine equation and reduced on-line calculation time. Based on the discrete controlled autoregressive integrated moving average (CARIMA) model, the control algorithm was combined with merits of adaptive control, which made control system possess of excellent robust and intelligent capability. At the same time, using for reference the thought of cascade control, generalized predictive control is combined in cascade structure. In the thickness loop of hydraulic AGC, it adopts PID control. And in the inner loop of screw-down servo system, it adopts generalized predictive control. It synthesizes merits of PID control, which possesses of easy algorithm, adjusting parameters conveniently and characteristic of generalized predictive control including of good tracking characteristic and strong robustness. The experimental result shows that adopted control strategies make system dynamic quality improved largely. Response time and control precision of screw-down servo system were improved. And the thickness precision of cold rolling strip was improved too.