Research on Cascade Predictive Control in Hydraulic AGC of Cold Rolling Mill

Abstract-Because the request to the quality of cold rolling sheet strips is higher and higher, the hydraulic AGC (Automatic Gauge Control) has been a requisite means for improving the quality of cold rolling strips´ finished products. But the PID control strategy, being comprehensively used in the locale, is difficult to satisfy the request of improving the control precision of cold rolling mill, because robustness is not very strong. The dynamic matrix control, brought forward by Cutler, is one of predictive control theories. It adopts the non-parameter model based the step response of the controlled object, and adopts strategies of multi-step prediction, receding-horizon optimization and feedback correction, which has the good tracking characteristic. The dynamic matrix control has succeeded to be applied in the industry field, so it is indispensable and feasible to explore its application in the hydraulic AGC system of the cold rolling mill. But the step response of the whole hydraulic AGC can´t be gained easily in the practical project, so it restricts the application of the dynamic matrix control in the hydraulic AGC. In this article, using for reference the thought of the cascade control, the predictive control is combined in the cascade structure. In the thickness loop of the hydraulic AGC, it adopts PID control. And in the inner loop of the screw-down servo system, it adopts the dynamic matrix control. The cascade predictive control in this article solves the problem of gaining the step response of the whole hydraulic AGC difficultly. When adopting the dynamic matrix control, the state observer is constructed, which makes the control system have the state feedback form with the observer, strengthens robustness of the system by correcting the predictive model, and makes the system have the intelligence. It synthesizes merits of PID control, which possesses of the easy algorithm and adjusting the parameter conveniently, the characteristic of the dynamic matr- ix control including of good tracking characteristic and strong robustness. The result of the experiment shows that the adopted control strategy makes the dynamic quality of the system improved largely. The response time and the control precision of the screw-down servo system are improved. And the thickness precision of the strip is improved too.