Constrained PI(D) Algorithms (C-PID)

Abstract

Majority of control algorithms used in industrial processes is PID or PID modification and many of these is badly tuned. The reason for this is that the physical constraints of the manipulated variable are neglected. The PID algorithm, presented in the paper, is obtained by inverting the standard PID twice and it is able to handle the constraints. The first analytical inverting step results in a proper PID inverse. This is then transformed into a state-space model. The statespace model is then inverted again by using the same method which is applied in Globally Linearizing Control and taking into account the physical constraints of the manipulated variable. The constrained PID (C-PID) algorithm obtained this way is an anti reset wind-up algorithm which can be readily implemented. A possible design methodology is also proposed. At the same time, regarding processes with not higher than second order dynamics, the solution a rigourous model-based one.