Optimality characteristics of PI/PID controllers: A combined min-max/ISE interpretation

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Abstract

This communication addresses the tuning of PI and PID controllers on the basis of the IMC approach. The tuning is based upon a first order plus time delay (FOPTD) model and aims to achieve a step response specification. Through analysis it has been found that by using the IMC approach we get a PI or a PID depending on the rational approximation used for the time delay term. This article raises the question that the use of a PID instead of a PI controller should be based on another reason more related to the control objectives rather than the use of a better approximation for the time delay. An alternative tuning is presented here, from within the IMC formulation, based on a min-max optimization. From the tuning rule provided by this approach the optimum settings from an integral squared error criterion point of view are derived. The optimal controller results in being a PI controller. From this optimal controller as the starting point, the introduction of the derivative action can be seen as a detuning procedure that can increase the robustness of the controller. This approach provides further insight into the tuning of PI and PID controllers giving the (alternative) parameters a precise engineering meaning. © Taylor & Francis Group, LLC.
Original languageEnglish
Pages (from-to)1240-1260
JournalChemical Engineering Communications
Volume197
Issue number9
DOIs
Publication statusPublished - 1 Sep 2010

Keywords

  • FOPTD models
  • Min-max optimization
  • PID tuning
  • Robustness

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