MAXIMUM GAIN RULE FOR SELECTING CONTROLLED VARIABLES

The appropriate selection of controlled variables is one of the most important tasks in plantwide control. In this paper, we consider the choice of secondary controlled variables for indirect control. The objective is to keep the primary variables close to their desired setpoint at steady-state without controlling them directly. We use the maximum scaled gain rule (maximize minimum singular value) and compare it to the exact local method. The issue of input scaling has usually been neglected, but it is shown that it may be crucial for ill-conditioned plants. The application is the selection of control structures for a binary distillation column.