Carsten Skovmose Kallesøe

Pressure Regulation in Nonlinear Hydraulic Networks by Positive and Quantized Controls

We investigate an industrial case study of a system distributed over a network, namely, a large-scale hydraulic network which underlies a district heating system. The network comprises an arbitrarily large number of components (valves, pipes, and pumps). After introducing the model for this class of networks, we show how to achieve semiglobal practical pressure regulation at designated points of the network by proportional control laws which use local information only. In the analysis, the presence of positivity constraints on the actuators (centrifugal pumps) is explicitly taken into account. Furthermore, motivated by the need of transmitting the values taken by the control laws to the pumps of the network in order to distribute the control effort, we study the pressure regulation problem using quantized controllers. The findings are supported by experimental results.

Plug and Play Process Control Applied to a District Heating System

Abstract The general ideas within plug and play process control (P 3 C) are to initialize and reconfigure control systems just by plug and play. In this paper these ideas are applied to a district heating pressure control problem. First of all this serves as a concrete example of P 3 C, secondly some of the first techniques developed in the project to solve the problems in P 3 C are presented. These are in the area of incremental modelling and control and they make it possible to “plug” in a new sensor and actuator and make it “play” automatically.

Proportional and Proportional-Integral Controllers for a Nonlinear Hydraulic Network

Abstract We consider the problem of regulating to a reference value pressures across components in a nonlinear hydraulic network of a reduced-size yet meaningful district heating system with two end-users. Exploiting the analogy between electrical and hydraulic networks, we derive a nonlinear model for the system. Then we design and analyze a proportional and a proportional-integral controller which guarantee semi-global practical and, respectively, asymptotic regulation of the pressures.

Quantized controllers distributed over a network: An industrial case study

We consider the problem of regulating pressures across large-scale hydraulic networks. We investigate the use of a class of piece-wise constant control laws which take value in a finite number of values and whose transition from one value to another occurs when the measurements cross certain thresholds. We show that these controllers guarantee set-point pressure regulation with an arbitrarily large domain of convergence. The use of this class of control laws is motivated by the need to exchange information among controllers distributed over the network.

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 Hybrid Model of a Brushless DC Motor

This paper presents a novel approach to modeling of a brush-less direct current motor (BLDCM) driven by an inverter using hybrid systems theory. Hybrid systems combine continuous and discrete (event-based) dynamics, which is exactly the case in an inverter-driven BLDCM. The model presented in this work consists of a general automaton with discrete states, combined with a set of continuous dynamic equations describing the electro-mechanical behavior of the motor. One of the significant benefits of this strategy is that the model describes the motor under all possible operating conditions. The model is derived for the common case of a BLDCM in wye-connection with a three-leg inverter. The model is verified on a real BLDCM drive and shows good agreement with experiments.

IEEE Multi-Conference on Systems and Control

Pressure management in water supply systems is an effective way to reduce the leakage in a system. In this paper, the pressure management and the reduction of power consumption of a water supply system is formulated as an optimization problem. The problem is to minimize the power consumption in pumps and also to regulate the pressure at the end-user valves to a desired value. The optimization problem which is solved is a nonlinear and non-convex optimization. The barrier method is used to solve this problem. The modeling framework and the optimization technique which are used are general. They can be used for a general hydraulic networks to optimize the leakage and energy consumption and to satisfy the demands at the end-users. The results in this paper show that the power consumption of the pumps is reduced.

Modeling of water supply systems: Circuit theoretic approach

Water leakage is an important component of water losses. Many methods have emerged from urban water supply systems for leakage control, but it still remains a challenge in many countries. To have better understanding of leakage in water supply system (WSS), to control leakage effectively and for optimal design of WSS, suitable modeling is an important prerequisite. In this paper first, the mathematical expression for pressure drop over each component of the water supply system such as pipes, pumps, valves and water towers is presented. Then the network model is derived based on the circuit theory 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.

Input selection for return temperature estimation in mixing loops using partial mutual information with flow variable delay

In hydronic heating systems for buildings a mixing loop is often used to control the temperature and pressure. An important task of a mixing loop is to control or constrain the return temperature since this leads to energy savings by reducing heat loss and energy consumed by the pump. With increased access to data, it is desirable to create a data driven model for control. Due to the abundance of data available a method for input variable selection (IVS) is used called partial mutual information (PMI). The paper introduces a method to include flow variable delay into the PMI framework. Data from an office building in Bjerringbro, Denmark is used for the analysis. It is shown that mutual information and performance of a generalized regression neural network (GRNN) is improved by using flow variable delay compared to constant delay.

Stability of drinking water distribution network

We strive to prove stability of a hydraulic network, where the pressure at the end user is controlled with PI control. The non-polynomial model is represented by numerous polynomial systems defined on sub-sets of ℝn. The sub-sets are defined by compact basic semi-algebraic sets. The stability of the PI-controller is proved by designing a Lyapunov function which fulfils different criteria in different sub-sets of ℝn. We find a polynomial Lyapunov function for the system using SOSTOOLS supported by Putinars Positivstellensatz.