Brief Ensuring monotonic gain characteristics in estimated models by fuzzy model structures

  • Authors:
  • Peter Lindskog;Lennart Ljung

  • Affiliations:
  • Department of Electrical Engineering, Linköping University, S-581 83 Linköping, Sweden;Department of Electrical Engineering, Linköping University, S-581 83 Linköping, Sweden

  • Venue:
  • Automatica (Journal of IFAC)
  • Year:
  • 2000

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Abstract

We consider the situation where a non-linear physical system is identified from input-output data. In case no specific physical structural knowledge about the system is available, parameterized grey-box models cannot be used. Identification in black-box type of model structures is then the only alternative, and general approaches like neural nets, neuro-fuzzy models, etc., have to be applied. However, certain non-structural knowledge about the system is sometimes available. It could be known, e.g., that the step response is monotonic, or that the steady-state gain curve is monotonic. The main question is then how to utilize and maintain such information in an otherwise black-box framework. In this paper we show how this can be done, by applying a specific fuzzy model structure, with strict parametric constraints. The usefulness of the approach is illustrated by experiments on real-world data.