Date of Award

2005

Document Type

Master Thesis

Degree Name

Master of Engineering (Research)

Department

Electronics Engineering

First Advisor

Dr. Tom O'Mahony

Second Advisor

Dr. Barry O'Connor

Abstract

The basic PID controller remains the most commonly used automatic feedback control technique in industry. Many tuning techniques exist for this controller and the use of tuning rules remains very popular, both in industry and academia. This thesis is concerned with the practical evaluation of a selected number of PID tuning rules. The rules were to be evaluated on an industrial pilot-scale milk pasteurisation process. However, most of these rules could not be tested on the real plant as the industrial distributed control system was quite inflexible and did not permit many of the more advanced PID structures e.g. two-degree of freedom controllers, to be implemented.

A first contribution of this thesis was therefore to design and implement a control platform suitable for scientific research. This platform is based on a PC with a data acquisition card and standard CAD software and provides the flexibility to implement the structures that are investigated. Subsequently, a first-order lag plus delay-type model was identified. Five recent tuning rules are applied to this model and evaluated on the pasteurisation process. All five controllers yield improved performance (reduced overshoot and steady-state variance) relative to the existing PI controller. The results clearly demonstrate that these rules are worthy replacements of the traditional Ziegler-Nichols method. Simultaneously, the results illustrate the benefits that can accrue from a simple controller re-tuning exercise. In this application, the main economic implication is that less energy is required however, lower pasteurisation temperatures have the added benefit of enhancing product taste. Subsequently, cascade control was proposed as an alternative to the single-loop PID controller. It is shown, that for this system, the primary benefit of cascade control is reduced response time.

A second contribution of this thesis is the development of a virtual lab. This virtual lab uses a non-linear model of the pasteurisation process to create an accurate simulation of the process, and offers a friendly graphical interface for the plant. This virtual lab can be accessed over the Internet, through a normal HTML browser. A set of laboratory exercises were developed to introduce the concepts of system identification and controller design to third and fourth-year engineering students. A web site was developed to facilitate this process.

Access Level

info:eu-repo/semantics/openAccess

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