Simulation and optimal control of water distribution system

Pao Yue-kong Library Electronic Theses Database

Simulation and optimal control of water distribution system


Author: Yu, Lap-ho
Title: Simulation and optimal control of water distribution system
Degree: M.Sc.
Year: 1997
Subject: Plumbing
Water -- Distribution
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: xiv, 76, [74] leaves : ill. ; 30 cm
Language: English
Abstract: This paper presents a control methodology for determining optimal pumping schedules for a water distribution system to obtain the least operation cost. The current dynamic programming optimization algorithm is a discrete control. It provides the feasible solutions to the problem and the control variables are allowed to change at fixed time. Continuous monitoring and control are adopted with state increment dynamic programming to minimize energy cost of a pumping station and number of pump switches. This algorithm is evaluated by comparing with the real operation and dynamic programming control algorithm. Explicit and implicit constraints including the allowable maximum daily cumulative pump switches, operating range of nodal pressures and water surface elevations of service reservoir restrict the admissible state and control variables during the planning time horizon. The water is mainly delivered to schools and residential buildings from the pumping system being studied. An extensive manpower deployment for night shifts, excessive pump and valve switches were required to achieve a predetermined water storage at a specific timing of a day. The equipment life was thus shortened. A control strategy is performed when an operational constraint is violated or the control time period is expired. If the water level of service reservoir increases or drops beyond the allowable values, the pump is selected to correct the level by turning it on or off as required. This strategy improves the daily operation and reduces the energy cost. It includes a set of control rules to determine the pump combinations at the defined time period. A controller is used to search for a suitable pump combination with the least power consumption to satisfy the instantaneous system operating conditions. The dynamic optimized pump scheduling takes account of water storage and the electricity tariffs to minimize the overall operating costs over a particular control period. Each component of the pumping system was modelled individually and was described by a set of differential and algebraic equations. The outputs of one model became the inputs of other model in the simulation. The information transferred from one to another corresponds to the practical operational process of the system. The algorithm iterated between the optimization model and the simulation model until an optimal solution was found in TRNSYS. The computational results show that the control strategy is able to reduce the number of pump switches and that there is an optimal range of water levels within which the water delivery costs is minimum in state increment dynamic programming control algorithm.

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