Multivariable control of a paper coloring process: a case study

Multivariable control of an industrial paper coloring process is studied with the aim of assessing the robustness of the resulting closed loop system, as well as the practicality of control implementation. With regard to this objective, two approaches were investigated: H_∞ robust control, and PI control with decoupling. The closed-loop properties of the resulting systems are compared by simulations. Both approaches have comparable robustness with respect to uncertainty in process parameters. However H_∞ control shows better properties with respect to the unmeasured disturbances in the form of added recycled paper. This paper provides an improved controller design over the previously proposed gain scheduling approach. Our single H_∞ controller provides good performance over a wide range of operating points without the necessity of renewed process identification at each setpoint