K. Malinowski

On-line hierarchical control for steady-state systems

This paper presents the basic principles and main properties of hierarchical control structures, which can be applied in steady-state optimization of complex systems. An essential feature of the structures considered in this paper is the use of feedback from the controlled system, along with the mathematical models. Suitable iterative procedures, preferably starting from the open-loop optimum, are proposed and investigated at some length. The stress of most of the discussion is on inequality constraints and on model-reality differences, which are unavoidable in any application of computer control.

Brief paper: Controllability and observability of expanded systems with overlapping decompositions

The expanded system concept of Siljak and his coworkers enables the design of robust overlapping controllers and observers for large scale systems to be carried out in a purely decentralised way. In this paper, we study the stability and detectability properties of expanded systems and show that it is only in certain special cases that these properties are preserved when the system is expanded. These special cases define the classes of systems where the expanded system concept can be used for controller or observer design.

Hierarchical Structure with Repetitive Goal Coordination for Real-time Flood Control in a Multireservoir System

Abstract The paper presents a hierarchical control structure for real time flood control in a multireservoir system. The aim of the structure is to minimize the flood damages which depend on the peak water levels at the most important locations situated far downstream the reservoirs. Water releases form the individual reservoirs are adjusted by the local operators while the objective of a central authority is to modify local performance functions so as to achieve his overall goals. Due to highly uncertain forecasting of future inflows the decision mechanism of a central dispatcher is based upon fast simulation of the system operation under different flow scenarios. An application of the control structure to a case study multireservoir system is shortly described together with some selected simulation results.

Decentralized Control Design: An Overview

Abstract In this paper we give an overview of decentralized decision making and control research and try to discern its trends. We first examine the decentralized structures which arise in a number of application areas. We then consider the stabilization of composite systems which are subjected to decentralized information constraints and we also examine appropriate design techniques for such systems. This is followed by a presentation of the basic results on stochastic decentralized and partially decentralized control problems where non-classical information patterns arise. Decentralized state estimation is also briefly discussed and the robustness issues in decentralized control are addressed. Some conclusions are then given on promising future research directions.

Problems in the design of multilayer, multiechelon control structures

Abstract Experience in the process industries has demonstrated that hierarchical (multiechelon and multilayer) control concepts are valuable in control system design. However, to date there has been relatively little work on the development of a unified approach to hierarchical control system design. This paper defines the design problem, notes several fundamental design questions and presents some initial answers applicable to process control problems.

Applicability of the Lagrange multiplier method to the optimization of quadratic systems

Conditions under which the Lagrange multiplier method (LMM) can be applied to optimization of the class of quadratic systems are considered. It is shown that quadratic systems can be optimised by LMM under rather general, and to some extent constructive, assumptions. The applicability of the results is illustrated with examples.

Practical Aspects of Coordination Processes

Abstract The practical issues concerning coordination processes are considered. It is assumed that the information as received by the coordinator is imperfect due to finite accuracy of data transmission and of local problems solutions. Also, the coordination process has to be stopped after a finite number of iterations. Two general basic coordination strategies are examined and the impact of information constraints on these strategies is evaluated. Then the requirements with respect to accuracy parameters are discussed and the dynamic adjustment of these parameters is discussed. It is shown that it should be possible to economize the coordination process when sufficient a priori information is available.

Hierarchical Dispatching Control Structure for a Multireservoir System

Abstract Operation of a complex water resource system is considered. The control structure involves local operators and a central system dispatcher which form together a two-level management hierarchy. The basic goals to be met-under considerable uncertainty with respect to future natural inflows and water demands - include keeping the reservoir levels within prescribed ranges and minimizing the specified performance index. The proposed control mechanism is based upon repetitive hierarchical optimization and upon more frequent and simpler correction actions. The fulfilment of both control objectives is investigated with special attention given to the first objective. Then a practical case study is described together with specific modifications of the considered control mechanism and with numerical results obtained through simulation of system operation.

Price coordination mechanism and control of steady-state processes

Abstract Control structures for large-scale steady-state processes are considered. Their task consists in setting up the proper values of manipulated variables for direct process controllers. Thus the proposed structures performs control functions of the second layer or optimizing controller in the functional control hierarchy. Since the controlled process is assumed to be partitioned into interconnected sub-processes, the second layer controller is organized into the form of a two level hierarchy of decision making units. The actions of local units are coordinated by the second level supremal controller in order to achieve satisfactory overall performance.

Long term resources allocation for control purposes in a water management system / L'attribution des ressources à long terme aux fins de contrôle dans un système d'économie des eaux

Abstract To represent both a centralized and a decentralized decision-making structure, water resource and quality management tasks are modelled for use in a single computer and a multicomputer system by applying price co-ordination for solving the long term optimization of the system. An example is given of the application of the decentralized management scheme to the water resources system of the Upper Silesia region in Poland.