PID Self-Tuning Controllers Used in Different Structures of the Control Loops

Abstract

The paper investigates the behavior of digital PID self-tuning controllers (STC) in different structures of the control loops used in adaptive systems. In the two phases of this type of systems which use a STC-PID, the first phase, i.e. the task of recursive identification of the plant model parameters, is used a regression (ARX) model with the recursive least squares method. Because the quality of process model depends on the order of the ARX model and of the sample period (Ts), the digital PID parameters are functions of these variables and, supplementary, of continuous-time PID parameters and of the control loop structures used in the adaptive system (although, not so largely as the firstly three variables). To see the latter influence, in this paper are considered two control loop block diagram, and for simulations - three different processes (stable; with no minimum phase; unstable), and some simulations with different . The PID controller design method used to obtain the specs desired for control loop dynamic behavior was the pole assignment method of the loop.