Constrained nonlinear multivariable control of a catalytic reforming process

The ability to handle constraints, which generally are non-linear functions of input, state and output variables, is an important feature for industrial control algorithms when they are applied to real processes. In this chapter, the basic assumptions and concepts about the non-linear process and constraints are defined. A non-linear constrained optimization strategy for handling the constraints is proposed and applied to the catalytic reforming reactor section which minimizes a function of the slack variables and allows a balance to be sought between the process outputs tracking their reference trajectories and constraint violation. In this manner, constraint variables can be controlled to the constraint limits as well as to the rate of approach to the constraint limit. Slack variables defining the trajectory departure from the chosen specification curves are added to the generic model control (GMC) control law for both the control variables and the constraint variables. The solution of the problem then becomes a non-linear constrained optimization, which minimizes a function of the slack variables.