Identification of processes in closed loop-identifiability and accuracy aspects

  • Authors:

  • I. Gustavsson;L. Ljung;T. Söderström

  • Affiliations:

  • Department of Automatic Control, Lund Institute of Technology, Box 725, S-220 07 Lund 7, Sweden;Department of Automatic Control and Systems Analysis, Institute of Technology, Uppsala University, S-751 21 Uppsala, Sweden;Department of Automatic Control, Lund Institute of Technology, Box 725, S-220 07 Lund 7, Sweden

  • Venue:
  • Automatica (Journal of IFAC)
  • Year:
  • 1977

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Abstract

It is often necessary in practice to perform identification experiments on systems operating in closed loop. There has been some confusion about the possibilities of successful identification in such cases, evidently due to the fact that certain common methods then fail. A rapidly increasing literature on the problem is briefly surveyed in this paper, and an overview of a particular approach is given. It is shown that prediction error identification methods, applied in a direct fashion will given correct estimates in a number of feedback cases. Furthermore, the accuracy is not necessarily worse in the presence of feedback; in fact optimal inputs may very well require feedback terms. Some practical applications are also described.