All these methods have in common that at each level a key point is to check if there
are enough manipulated variables to meet the constraints and to optimize operation. The
methods are easy to follow and give a good process understanding, and the concept of a
hierarchical view is possible to combine with almost any design method.
Hierarchical decomposition based on control objectives
The hierarchy based on control objectives is sometimes called the tiered procedure. This
bottom-up procedure focuses on the tasks that the controller has to perform. Normally one
starts by stabilizing the plant, which mainly involves placing inventory (mass and energy)
controllers.
Price et al. (1993) build on the ideas that was introduced by Buckley (1964) and they
introduce a tiered framework. The framework is divided into four different tasks:
I Inventory and production rate control.
II Product specification control
III Equipment & operating constraints
IV Economic performance enhancement.