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Reduced Order Internal Models in the Frequency Domain

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Original languageEnglish
Pages (from-to)1806-1812
JournalIEEE Transactions on Automatic Control
Issue number6
Publication statusPublished - 2018
Publication typeA1 Journal article-refereed


The internal model principle states that all robustly regulating controllers must contain a suitably reduplicated internal model of the signal to be regulated. Using frequency domain methods, we show that the number of the copies may be reduced if the class of perturbations in the problem is restricted. We present a two stage design procedure for a simple controller containing a reduced order internal model achieving robust regulation. The results are illustrated with an example of a five tank laboratory process where a restricted class of perturbations arises naturally.


  • Adaptive control, Aerospace electronics, Frequency control, Frequency-domain analysis, Linear systems, Mathematical model, model/controller reduction, output tracking, robust control, Robustness, Uncertainty

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Field of science, Statistics Finland