Applications

Interactive Learning Modules for PID Control

by José Luis Guzmán, Karl J. Åström, Sebastián Dormido, Tore Hägglund, Yves Piguet

The interactive learning modules have been developed to make it possible to quickly obtain a good intuition and a good working knowledge of PID control. It is part of a series of modules that are designed as a complement to the book [1], where the modules can be viewed as an attempt to make the key pictures in the book interactive. The modules consist of menus where process transfer functions and PID controllers can be chosen, parameters can be set, and results stored and loaded. A graphic display which shows time or frequency responses is a central part. The graphics can be manipulated directly by dragging lines, points or curves or by using sliders. Parameters that characterize robustness and performance are also displayed. At the moment, three modules have been developed., More modules are under development. The central module is called PID Basics, two auxiliary modules PID Loop Shaping and PID Windup illustrate loop shaping and windup.

PID Basics

It is a module designed to make you familiar with PID control. The module gives time and frequency domain views of the responses of a closed-loop system consisting of a PID controller and a process model. Many process models can be selected, controller parameters can be changed interactively, and the resulting responses are displayed instantaneously.

PID LoopShaping

Loop shaping is a design method where it is attempted to choose a controller such that the loop transfer function obtains the desired shape. In this module the loop transfer function is illustrated by its Nyquist plot. The module shows the Nyquist plots of the process transfer function P(s) and the loop transfer functions L(s)=P(s)C(s). It can be shown how the loop transfer functions change when controller parameters are changed and conversely what parameters are required to obtain a given shape of the loop transfer function.

PID Windup

The purpose of this module is to give a familiarity with the phenomenon of integral windup and a method for avoiding it, see [1]. The module shows process outputs and control signals for unlimited control signals, limited control signals without antiwindup, and limited control signals with antiwindup. Process models and controller parameters can be selected in the same way as in the other modules. The saturation limits of the control signal can be determined either by entering the values or by dragging the lines in the saturation metaphor.

Reference

[1] Karl Johan Åström and Tore Hägglund. Advanced PID Control. ISA - The Instrumentation, Systems, and Automation Society, Research Triangle Park, NC 27709, 2005.

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