This thesis considers the design of cascaded SISO control systems using the H∞
and QFT methodologies. In the first part of the thesis the actual advantages offered by
Single Input Single Output (SISO) cascade loop structures are studied. In Quantitative
Feedback Theory(QFT) it is emphasized that the use of cascaded loops is primarily for
the reduction of bandwidth of the controllers. This in turn helps in considerable
reduction of the adverse effects of high frequency noise. The question that arises then is
whether or not there are any substantial benefits to be gained by cascade loop design in
the low frequencies. It is shown using QFT methodology that there arent any advantages
gained in the low frequencies with the use of cascaded design. In effect it is concluded
that if the design is properly executed a single loop controller closed from the output to
the input will be sufficient to meet the typical performance specifications. This is shown
using an example where the mold level of a continuous casting process is to be
controlled. The plant being used has considerable uncertainty so that features of robust
control can be highlighted.
In the second part the Robust Outer Loop bounds were generated analytically and
examined for certain properties. It was compared to the bounds generated by already
existing algorithms.
In the third part the inner outer QFT design was modified with the inner loop
being designed using H∞ with the concept of sensitivity shaping. This design was very
similar to the pure QFT design with the added advantage of having some automation.
In the fourth part the H∞ methodology was used to design a two loop control
structure. The idea was to compare this design to the QFT design. It was seen that H∞
generated redundant controllers and pre filters.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/1520 |
| Date | 17 February 2005 |
| Creators | Lal, Mayank |
| Contributors | Jayasuriya, Suhada |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 540634 bytes, electronic, application/pdf, born digital |
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