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An approach to control system design is described, based on an extension of the multilevel control concept. In essence, the problem is divided into simpler subproblems: (a) The controlled process is decomposed into a number of subprocesses, each with its own control system operating on a local suboptimal performance criterion; (b) each subprocess controller is decomposed into a hierarchy of control functions which distribute the load and responsibility for satisfying the control objective. The primary effort of the paper is in the development of the control hierarchy as a useful concept in control system design and implementation. The hierarchy is described in the context of the multilevel approach; however, an important distinguishing feature is the association of levels with disturbance sets roughly classified according to the frequency dependency of their effects on the overall performance. Also associated with the hierarchy is an ordering with respect to time scale, complexity of computation, degree of uncertainty, and so on, which relate to important design considerations for the overall system.

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The cost-performance tradeoff problem associated with a multilayer control system for controlling a class of static.nonlinear. multivariable systems is considered. The multilayer control system has a , number of layers of control functions each of which updates different subsets of the manipulated variables at different costs.A favorable cost-performance tradeoff is achieved by determining at each control decision time which subset of the control variables is to~e updated. In this paper, we present a mathematical rrodel which describes the operation of the multilayer control system. Also we show that the problem of determining a. decision rule (policy) which results in an optimal cost-performance tradeoff can be formulated as a problem in Markovian Decision Processes. Consequently, an optimal policy can be identified by solving a linear program.In order to reduce the computational effort required for identifying the optimal policy, a class of parameterized policies is introduced based on~measure of deviation of the disturbance. This approach provides a designer with a practical method of determining a control policy which achieves a favorable cost-performance tradeoff.An example is given for demonstrating a possible application to process control.-1 -