Computation of stabilizing PI-PD controllers

The PI-PD controller structure provides an excellent four-parameter controller for control of integrating, unstable and resonant processes to set point changes while the conventional PID controller has limitations in controlling such systems. In this paper, a graphical method for the computation of all stabilizing PI-PD controllers is given. The proposed method is based on plotting the stability boundary locus, which is a locus dependent on the parameters of the controller and frequency, in the parameter plane. The stability boundary loci are first obtained in the (K _d , K _f ) and (K _p , K _i ) planes and then it is shown that all the stabilizing values of the parameters of a PI-PD controller can be found. Computation of stabilizing PI-PD controllers which achieve user specified gain and phase margins is also studied. The method is used to design robust PI-PD controllers for control systems with parametric uncertainties. A design procedure for interval control systems is proposed. Examples are given to show the benefit of the method presented. Recommended by Editorial Board member Jietae Lee under the direction of Editor Young Il Lee. Nusret Tan was born in Malatya, Turkey, in 1971. He received his B.Sc. degree in Electrical and Electronics Engineering from Hacettepe University, Ankara, Turkey, in 1994. He received the Ph.D. degree in Control Engineering from University of Sussex, Brighton, U.K., in 2000. He is currently working as an Associate Professor in the Department of Electrical and Electronics Engineering at Inonu University, Malatya, Turkey. His primary research interest lies in the area of systems and control.