Interactive Tool for Frequency Domain Tuning of PID Controllers

Abstract

This paper presents an interactive tool focused on the study of proportional-integral-derivative (PID) controllers. Nowadays, PID control loops are extensively used in industrial applications. However, it is reported that many of them are badly tuned. From an educational point of view, it is essential for undergraduate students in control engineering to understand the importance of tuning a control loop correctly. For this reason, the tool provides different PID tuning methods in the frequency domain for stable open-loop time-delay-free processes. The different designs can be compared interactively by the user, allowing them to understand concepts about stability, robustness, and performance in PID control loops. A survey and a comparative study were performed to evaluate the effectiveness of the proposed tool.Processes 2018, 6, 197 2 of 20 response using time-domain metrics [12]. Other methods propose a tradeoff between performance and robustness, or between servo and regulation modes [13,14]. However, most of these methodologies are usually based on a simple model of the dynamics of the process, and a previous model reduction is necessary. Other methodologies based on the frequency response allow PID design for any arbitrary order irrational or non-minimum phase stable transfer functions [3,15]. These methods use robustness conditions in the frequency domain, such as phase margin, gain margin, maximum sensitivity, and so on [16].This work reports the design and application of an interactive Matlab-based tool focused on tuning and simulation of single input single output (SISO) PID controllers for stable processes without time delay. The objective is the application and teaching of PID tuning methods based on frequency response specifications supported by a graphical interpretation. The proposed tool has been developed using the basic features of Matlab 2012b (MathWorks, Natick, MA, USA) [17] without adding extra toolboxes, and provides a set of PID tuning methodologies in the frequency domain for stable processes. Although there is a growing trend regarding the exploitation of open source tools for educational purposes, the reliability and widespread use of the Matlab suite in the academic world can be pointed to as one of its main benefits. Interactive software for teaching control is supported for several reasons [18][19][20][21][22]: (a) Learning efficiency can be increased by using computer aided design and analysis tools; (b) modifying properties and instantaneously observing the corresponding effects is very helpful both for design and learning processes; (c) these tools support the combination between theory and practice contents; (d) the interactive comparison of designs based on different frequency domain specifications allows one to understand fundamental ideas about stability, robustness, and performance in PID control loops.An initial version of the tool was presented in a conference article [16]. In the current work, the tool has been applied for educational purposes, and has been improved and incr...

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