An LMI tuning technique for robust constrained cross-direction controllers

Abstract

The paper machine cross-directional (CD) process is a web forming process whose target is to produce paper sheets with uniform properties. Industrial CD controllers are designed to attenuate the effects of the disturbances while providing robustness against modeling uncertainties. Although the CD process actuators are subject to constraints, the industrial practice is to tune CD controllers ignoring the process constraints due to the large scale control design problem. The robustness of CD feedback loops to the nonlinearity in a constrained internal model controller (IMC) and plant uncertainty were shown to satisfy an integral quadratic inequality. This work develops a loop-shaping technique for the large-scale CD process through a pseudo singular value decomposition approach. Tuning the constrained IMC CD controller for robust stability and performance is formulated as one linear matrix inequality (LMI) feasibility problem. The performance of the constrained IMC CD controller is investigated through comparing it to an industrial model predictive controller (MPC) CD controller.