Beta 1


Title MIMO control of refrigeration systems
Author Knudsen, Lars Søllingvraa
Supervisor Niemann, Hans Henrik (Automation and Control, Department of Electrical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Blanke, Mogens (Automation and Control, Department of Electrical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2009
Abstract It has long been the tradition in supermarket refrigeration systems, to control each display case individually, often with the use of simple hysteresis control. This type of control has the advantages of being easy to design and maintain. However this can present problems with valve syncronization and with that reduction of compressor lifetime. To combat this problem, a solution is suggested in this project to utilize the priciples of robust control and the Youla parametrization, to achieve both robustness and good performance in the control of centralized refrigeration systems. This is done using centralized control, using 2 or more controllers. One can then have robust propertied while another had good performance, and they can then be used at dierent times. The problem with using this method is switching between the controllers while the system is running, without having a negative eect on the system. To achieve the switches with no ill eect to the system, a solotion based on the Youla parametrization is presented. This solution consists of the implementation of the Youla parametrization with a Q calculated to switch between controllers by slowly tuning Q from 0 to full value when a switch is to occur. In order to prove that the setup is functional, a model developed by Danfoss and augmented with noise sources and changes in airload simulating relling of the case for 10 minuted every other hour is utilized. To illustrate the concept of switching between two controllers, 2 controllers based on LQG control, a special case of H2 control, has been developed. The Youla setup is then implemented, and Q is calculated to switch between the controllers. To reduce the order of the system, model reduction methods have been presented using balanced order reduction methods. Simulations show that the concept works, e.g. it is possible to switch from one controller to the other while the system is online with no ill eect. Through simulations it has been veried that the setup works under a range of situations, including switched while the system is not at a stable reference. It is however not possible at this time to evaluate weather or not the methods presented will have bigger advantages than the traditional setup, since this will require extensive testing on a physical system, and thus the next logical step is to start testing the setup on the test systems at Danfoss. II
Abstract Det har lnge vret en tradition i kleindustrien, at styre centralkleanlg ved at styre de enkelte klebokse hver for sig, ofte med simpel hysterese regulering. Dette har den fordel at vre let at udvikle samt let at servicere. Der kan dog opsta ere problemer ved denne metode, hvoraf et af de mest alvorlige er ventilsynkronisering som stter et strre pres pa kompressoren og dermed forkorter levetiden. Som et alternativ til denne traditionelle regulering, er der i dette projekt prsenteret en metode til bade at fa robust styring og god ydeevne i reguleringen af centrale klesystemer. Dette gres ved at anvende central styring, dog ikke med kun en regulator, men med 2 eller ere. Den nominelle regulator kan sa eksempelvist handtere systemet robust i tilflde af fejl, mens en anden regulator med bedre ydeevne kan kobles ind nar systemet krer som normalt. Problemet ved denne metode, er at skiftet skal forega mens systemet krer, uden at pavirke systemet negativt. For at opna dette er en lsning baseret pa Youla parametriseringen prsenteret. Denne lsning gar ud pa at implementere Youla parametrisering og sa udregne en Q der kan skifte fra en regulator til en anden ved at blive justeret op fra 0 til fuld vrdi over et tidsinterval. For at bevise at konceptet virker, anvendes en simuleringsmodel af et klesystem udviklet af Danfoss til at demonstrere funktionaliteten. For at tilnrme modellen den fysiske verden, er den blevet videreudviklet til at inkludere malestj samt at simulere opfyldning af kleboksen over en periode pa 10 minutter hver anden time. For at illustrere konceptet med at skifte fra en regulator til en anden, er der udviklet 2 regulatorer ved at anvende LQG regulering, et specialtilflde af H2 regulering. Derefter er Q udregnet saledes at faktoren kan anvendes til at skifte mellem de to regulatorer mens systemet er online. For at reducere systemordnen, er der foretaget modelreduktion pa Q, ved at anvende balancerede reduktionsmetoder. Simuleringer viser at princippet med at skifte regulator ved hjlp af Youla parametriseringen virker, altsa at det er muligt at skifte fra en regulator til en anden og tilbage igen mens systemet krer, uden at gre det ustabilt. Det er i simuleringer demonstreret at konceptet er 100% funktionelt under forskellige forhold, herunder skift bade nar systemet er i hvile ved referencerne og nar dette ikke er tilfldet. Det er dog ikke muligt at vurdere om fordelene er strre ved denne metode end ved traditionel styring fr omfattende tests pa et fysisk system er blevet udfrt. Dog har dette projekt demonstreret at konceptet fungerer, og det nste logiske trin er derfor at teste det i laboratoriet pa Danfoss. I
Imprint Technical University of Denmark (DTU) : Kgs. Lyngby, Denmark
Pages 126
Fulltext
Original PDF Lars_Soellingvraa_Knudsen_2.pdf (3.65 MB)
Admin Creation date: 2009-10-02    Update date: 2009-11-04    Source: dtu    ID: 250693    Original MXD