February 2010

Instrumentation

Implement a constrained optimal control in a conventional level controller - Part 2

Novel tuning method enables a conventional PI controller to explicitly handle the three important operational constraints of a liquid level loop in an optimal manner as well as copes with a broad range of level control from tight to averaging control

Lee, J. W., LG Chem, Ltd.; Lee, Y., GS-Caltex Corp.; Shin, J., LG Chem.

Part 1 of this article outlined the methodology. This part will discuss PI controller design for tightest constraint control and provide some examples. PI controller design for tightest constraint control. For a level loop being operated near the constraint, it is necessary to control the loop on the tightest possible constraint, the so-called "tightest constraint control": • For a given Hmax (or Q'o max), the PI controller for the tightest constraint control with respect to Q'o max (or Hmax) can be designed using either where t = 0.404. In this case, the tightest available Qo max is 1.3606 Qi or equivalently min 0.404. • For a given (Q'o max, Hmax) set

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