Process Control: Modeling, Design, and Simulation

11.4. Nonlinear PID Control

The fixed-parameter PID controller is ubiquitous in the process industries. The ideal PID controller has the form (see Chapter 5)

Equation 11.12

where it is understood that any bias associated with steady-state operation is absorbed into the integral term. Other forms for PID control are presented in Chapter 5.

Often it is useful to have a nonlinear controller even if the process is linear. A common example is level control of a surge drum where the primary objective is to maintain a reasonably consistent outlet flow under disturbances in the inlet flow rate, subject to high and low drum level constraints. In this situation, ...