Modeling and analysis of control structures for partially controlled plants

The modeling of control structures for plants that are decomposed into a primary and a secondary subsystem is treated. The main interest is the behavior of the primary system when the outputs of the secondary system are controlled. Often identification experiments in the process industry have to be performed under such conditions. The process model obtained applies for the particular control structure in use during the experiment. In this paper it is shown how models corresponding to arbitrary control structures can be derived once the model for one (arbitrary) control structure is known for the partially controlled plant. The models can be used for screening of control structures and design of controllers for the primary system. Distillation is used as an example