Modeling and control of a District Heating System
Author
Jochumsen, Anders
Term
10. term
Publication year
2010
Submitted on
2010-06-03
Pages
117
Abstract
Dette projekt undersøger, hvordan et modelbaseret reguleringssystem kan understøtte en ny, energibesparende infrastruktur for fjernvarme, hvor flere serieforbundne pumper i hovedledningen samt pumper ved forbrugerne muliggør mindre rørdimensioner og et konstant differenstryk hos hver bruger. Med udgangspunkt i en skaleret laboratoriemodel fra Grundfoss A/S med hovedledning, fire forbrugergrene, seks pumper, computerstyrede ventiler og differenstryksensorer udvikles en first-principles-model af rør, pumper og ventiler, hvis parametre estimeres ud fra målinger. Heraf afledes lineære og lineært parameterafhængige (LPV) tilstandsrum-beskrivelser, inklusive diskrete modeller og pumpeforsinkelse. En Extended Kalman Filter (EKF)-observatør designes til at estimere gennemstrømninger og forbrug udelukkende fra differenstrykmålinger; dens ydeevne vurderes som tilfredsstillende og kan dermed reducere behovet for direkte forbrugssensorer. To styringsstrategier undersøges: en lineær kvadratisk (LQ) regulator baseret på den lineære model, som designes, implementeres og viser tilfredsstillende tracking af en konstant differenstrykreference på tværs af varierende forbrug, samt LPV-metoder, der var planlagt men ikke blev implementeret på grund af omfattende numeriske problemer ved løsning af lineære matricelige uligheder. Samlet leverer arbejdet en eksperimentelt forankret model, observatør og regulator som grundlag for modelbaseret regulering af næste generations fjernvarmeinfrastruktur.
This thesis explores how a model-based control system can support a novel, energy-saving district heating infrastructure in which multiple series-connected pumps along the main line and at consumers enable smaller pipe diameters and constant differential pressure for each user. Using a scaled laboratory setup from Grundfoss A/S with a main pipe, four consumer branches, six pumps, computer-controlled valves, and differential pressure sensors, a first-principles model of pipes, pumps, and valves is derived and parameterized from measurements. From this, linear and Linear Parameter Varying (LPV) state-space descriptions are obtained, including discrete models and pump delay. An Extended Kalman Filter (EKF) observer is designed to estimate flows and consumptions based solely on differential pressure measurements; its performance is deemed satisfactory, reducing dependence on direct consumption sensors. Two control strategies are investigated: a Linear Quadratic (LQ) controller based on the linear model, which is designed, implemented, and shows satisfactory tracking of a constant differential pressure reference under varying consumption, and LPV methods that were planned but not implemented due to substantial numerical difficulties in solving Linear Matrix Inequalities. Overall, the work provides an experimentally grounded model, observer, and controller as a foundation for model-based control of next-generation district heating infrastructure.
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