Flow Ratio and Pressure Control in a Low Losses WDS – Analysis of Dynamics

Abstract

[EN] Société wallonne des eaux (SWDE) is the most important water production and distribution company in Wallonia, one of the regions in Belgium. Its distribution network stretches over 40,000 km. It covers nearly 200 municipalities and has more than one million connections. SWDE supplies drinking water to nearly 2.4 million people, constituting over 70% of the Walloon population. Recently, SWDE has launched a major multimillion-Euro project to improve security of the water supply in Wallonia. The project involves a 500/800 mm extension of a 1000 mm wide, over 100 km long pipeline as a backbone of the distribution network, starting from the Eupen and Gileppe reservoirs. The project created a number of engineering challenges and one of them is considered in this paper. It is concerned with the design of a feedback control scheme to achieve satisfactory operation in terms of water mixing from two sources and pressure stability in the new water distribution system (WDS). A feedback control strategy to maintain this constant ratio have been investigated. The objective was to check stability of the control scheme. The concern was about potential interactions between the PRV operation and the pump speed control loop. Matlab/Simulink which allows to model generic dynamic systems as well as control components has been selected as a modelling environment. A dynamic model of the WDS has been implemented following the general methodology developed by the authors and presented earlier in the literature. Pipes have been represented by the rigid column model, the PRV by behavioral model described by a first order differential equation and a pump by a first order inertial equation. In a low losses system, small changes of the pressure at the PRV outlet may cause significant changes in the flow, making the flow ratio control difficult. An important innovation was to introduce an additional TCV downstream to the PRV to increase head losses and reduce the interactions between the flow ratio control loop and the PRV. The paper presents results of an extensive simulation study of the control system behavior for different control parameters and time varying demands.