Hierarchical Control of Large Scale Chemical and Metallurgical Systems

Abstract

This paper reviews in an integrative manner some methodological and practical aspects of hierarchical control systems in large-scale chemical production complexes and steelworks made of many strongly or weakly interconnected processes sharing common resources. The paper presents practical problems about the production control within a multilevel “dispatcher” system. The recommended structure represents an attempt to implement multilevel philosophy and computing schemes within the frame of multiloop control systems consisting of a set of units operating in a decentralized but coordinated manner. The basic idea of the structure is that each unit, at any level, operating at different periods of time, “strives” to make local decisions that meet the recommended coupling variables trajectories previously agreed at the next higher level (generally using multilevel techniques). When some coupling outputs are not controlled in a satisfactory way, the higher level unit is activated. The methods are designed to meet the natural needs that occur when the human decision makers and operators are within the control system. An example of applying the proposed structure in industrial environment is presented. Some problems concerning static and dynamic optimization multilevel methods, open loop and closed loop decentralized highly reliable controllers are presented. All the elements may be considered as program modules of a computer package that supports a hierarchical control structure.