January 2010

Instrumentation

Implement a constrained optimal control in a conventional level controller - Part 1

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, M., Yeungnam University; Shin, J., LG Chem.

Due to the importance of liquid level loops for successful plant operation, extensive research has been done to enhance their control performance.1–9 A level controller is often required to not only minimize level deviation but also to provide nonaggressive control action. Controlling outflow behavior is as crucial as controlling the liquid level itself, especially when the outflow is situated upstream of a critical unit such as a reactor or a separation column. Furthermore, a liquid level loop generally has three important operational constraints: the rate of change in the outflow should be kept below an allowable limit for smooth control action, the level deviation should be within an

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