Development and Comparison of Two Hierarchical Structures for On-Line Control of a Water System—A Case Study

Abstract

In the paper two control structures for on-line control of a real water system are developed and comparative simulation study is performed. The system considered is a retention part of the Kamienna river catchment area. The basic physical components of the water system are: two water retention reservoirs, main river and its tributaries and two towns being the water users. The control goal consists in supplying desired daily quantities of water to users in towns and keeping a physical state of the system inside given constraints. Unknown system inflows are the source of uncertainty, but rich enough set of historical data enables to built the inflows prognosis. Due to the uncertainty timing and the reservoirs sizes the control problem time horizon has to be of one year lenght. To overcome the dimensionality problem a time aggregation concept is imployed. The result is a hierarchical control structure composed of three layers acting repeatedly with different frequency of intervention, based on the discrete system state measurements. The tasks of the upper layers are to generate the reservoirs targets for the third layer by solving long-term and mid-term optimization problems with different degree of time aggregation respectively. The third layer operation products obtained by solving short-term optimization problems are directly applied to the system. The inflows prognosis used in the optimization tasks for every layer are broght up to date in every moment of the layer intervention. Two versions of the short-term problems are proposed and investigated. The first version consists in direct determining daily releases of water from the reservoirs and daily quantities of water assigned to the towns. The second version is based on a decision rules concept. In the paper those two versions are compared by performing the exhaustive simulations of their operation.