Tom Nørgaard Jensen

Output Regulation of Large-Scale Hydraulic Networks

The problem of output regulation for a class of hydraulic networks found in district heating systems is addressed in this brief. The results show that global asymptotic and semiglobal exponential output regulation is achievable using a set of decentralized proportional-integral controllers. The fact that the result is global and independent of the number of end users has the consequence that structural changes such as end-user addition and removal can be made in the network while maintaining the stability properties of the system. Furthermore, the decentralized nature of the control architecture eases the implementation of structural changes in the network.

Quantized pressure control in large-scale nonlinear hydraulic networks

It was shown previously that semi-global practical pressure regulation at designated points of a large-scale nonlinear hydraulic network is guaranteed by distributed proportional controllers. For a correct implementation of the control laws, each controller, which is located at these designated points and which computes the control law based on local information only (measured pressure drop), is required to transmit the control values to neighbor pumps, i.e. auxiliary pumps which are found along the same fundamental circuit. In this paper we show that quantized controllers can serve well to this purpose. Besides a theoretical analysis of the closed-loop system, we provide experimental results obtained in a laboratory district heating system. This approach is fully compatible with plug-and-play control strategies.

Adaptive reference control for pressure management in water networks

Water scarcity is an increasing problem worldwide and at the same time a huge amount of water is lost through leakages in the distribution network. It is well known that improved pressure control can lower the leakage problems. In this work water networks with a single pressure actuator and several consumers are considered. Under mild assumptions on the consumption pattern and hydraulic resistances of pipes we use properties of the network graph and Kirchhoffs node and mesh laws to show that simple relations exist between the actuator pressure and critical point pressures inside the network. Subsequently, these relations are exploited in an adaptive reference control scheme for the actuator pressure that ensures constant pressure at the critical points. Numerical experiments underpin the results.

Toward model-based control of non-linear hydraulic networks

Water leakage is an important component of water loss. Many methods have emerged from urban water supply systems (WSSs) for leakage control, but it still remains a challenge in many countries. Pressure management is an effective way to reduce the leakage in a system. It can also reduce the power consumption. To have a better understanding of leakage in WSSs, to control pressure and leakage effectively, and for optimal design of WSSs, suitable modeling is an important prerequisite. In this paper a model with the main objective of pressure control and consequently leakage reduction is presented. Following an analogy to electric circuits, first the mathematical expression for pressure drop over each component of the pipe network (WSS) such as pipes, pumps, valves and water towers is presented. Then the network model is derived based on the circuit theory and subsequently used for pressure management in the system. A suitable projection is used to reduce the state vector and to express the model in standard state-space form.

A Distributed Algorithm for Energy Optimization in Hydraulic Networks

Abstract An industrial case study in the form of a large-scale hydraulic network underlying a district heating system is considered. A distributed control is developed that minimizes the aggregated electrical energy consumption of the pumps in the network without violating the control demands. The algorithm is distributed in the sense that all calculations are implemented where the necessary information is available, including both parameters and measurements. A communication network between the pumps is implemented for global optimization. The local implementation of the algorithm means that the system becomes a Plug & Play control system as most commissioning can be done during the manufacture of the pumps. Only information on the graph-structure of the hydraulic network is needed during installation.

Global asymptotic stabilization of large-scale hydraulic networks using positive proportional controls

An industrial case study involving a large-scale hydraulic network underlying a district heating system subject to structural changes is considered. The problem of controlling the pressure drop across the so-called end-user valves in the network to a designated vector of reference values under directional actuator constraints is addressed. The proposed solution consists of a set of decentralized positively constrained proportional control actions. The results show that the closed-loop system always has a globally asymptotically stable equilibrium point independently on the number of end-users. Furthermore, by a proper design of controller gains the closed-loop equilibrium point can be designed to belong to an arbitrarily small neighborhood of the desired equilibrium point. Since there exists a globally asymptotically stable equilibrium point independently on the number of end-users in the system, it is concluded that structural changes can be implemented without risk of introducing instability. In addition, structural changes can be easily implemented due to the decentralized control architecture.

Global Stabilization of Large-Scale Hydraulic Networks Using Quantized Proportional Control

Abstract An industrial case study involving a hydraulic network underlying a district heating system is investigated. The flexible structure of the network calls for control structure which is able to handle changes in the network structure. For this purpose a set of decentralized proportional controllers have been proposed. These controllers make use only of locally available information, and in order to make implementation of the control laws possible, the control signals are required to be communicated across the network. To accommodate this a quantized version of the control laws are considered, and the results show that the designed closed loop system maintains its stability properties despite the structural changes introduced in the system.

Application of a novel leakage detection framework for municipal water supply on AAU water supply lab

Water scarcity is an increasing problem worldwide and at the same time, a huge amount of water is lost through leakages in the distribution networks [1]. Detecting and isolating leakages fast is very important not only to save water but also to avoid destruction of roads and houses. This paper deals with isolation of leakages using a reduced network model. We propose a heuristic leakage detection/isolation algorithm which uses the reduced network model to estimate nominal behaviour. The model is adaptive and thus adapts slowly to changes in the network. However, some leakages change the behaviour instantly, and the deviation between pressures estimated by the reduced network model and the actual measured pressure indicates the location of the leakage. The proposed algorithm is tested on a specially designed laboratory setup that emulates a water distribution network. The test shows that the algorithm is in fact able to indicate in which area of the network a leakage has appeared.