The proportional-integral-derivative (PID) as well as the proportional-integral (PI) controller is the workhorse of the process industry. More than 99.9 percent of basic control systems rely on this controller. Even when model predictive control (MPC) is widely employed, a PI controller is normally used for flow control to deal with the nonlinearities of the installed flow characteristic and to enable flow ratio control.
For unmeasured disturbances, the PID has been proven to provide essentially optimal control (Bohl and McAvoy 1976). When fast and aggressive control is needed to prevent activation of a safety instrumented system (SIS) or relief device, a PID controller is necessary. A correctly ...