THE INTERFACE BETWEEN DESIGN AND CONTROL .3. SELECTING A SET OF CONTROLLED VARIABLES

By solving the optimum steady-state control problem in terms of the significant disturbances and manipulative variables, we often find that the optimum values of some of the operating and/or manipulative variables lie at constraints. If we select these constrained variables as controlled variables, the resulting feedback system will have near optimal performance without the need for measuring all the disturbances or for calculating the entire optimum steady-state control policy on-line. In many cases it is possible to propose heuristics to identify the constrained controlled variables.