Robust two-step controller design for a high-purity distillation column

A control scheme of combining two feedback loops to a single one is presented in this paper. The two different loops allow one to separate different control objectives, for instance performance and robustness. This design method is applied to a methanol-water distillation column to investigate the influence of the different loops on each other. It is shown that the inclusion of a physically reasonable feedforward control into the controller design collides with stabilizability. Furthermore, a robust controller design technique, similar to H_∞-design is introduced