Mirzaei, Mahmood

Siden energikrisen i 1972 har der været en stigende interesse i at udnytte energiresourser, der ikke er baseret på olie. Vindenergi er en af de mest lovende. Senere har bekymringen for global opvarmning øget interessen for grøn og vedvarende energi. Dette har intensiveret forskningen indenfor dette område. Vindmøller er klart de mest dominerende energisystemer indenfor vedvarende energi og håbet er at de indenfor den nærmeste fremtid kan konkurrere økonomisk med kraftværker baseret på fossile brandstof. Dette kræver imidlertid en forbedret teknologi for at reducere omkostningerne ved produktionen af elektrisk energi. Regulering kan spille en central rolle i den forbindelse. Dette skyldes først og fremmest at reguleringen kan reducere produktions omkostningerne ved at vindmøllerne køres mere effektivt. Dernæst kan reguleringen reducere udmattelses af strukturen såsom tårn og blade og derved forøge vindmøllers levetid.En vindmølles effektproduktion er groft sagt proportional med kvadratet af rotorens radius. Det virker derfor fornuftigt at øge størrelsen af vindmøllerne for at øge effektproduktionen. Desværre bliver bladenes vægt også forøget og med kubus af rotorradius. For at modvirke dette forhold må strukturen gøres lettere og med det resultat at strukturen bliver mere fleksibel.Regulering af vindmøllers fleksible struktur i et stokastisk vind felt er meget udfordrende. I denne afhandling er der fokuseret på en række forskellige robuste og modelbaseret metoder til regulering af vindmøller. Først er mu-syntese metoder egenskaber undersøgt i forbindelse med robust stabilitet og robust performance. Derefter er MPC regulatorer undersøgt i forbindelse med regulering af vindmøller. Disse giver gode resultater, specielt når der indgår målinger af vindhastigheden med LIDAR. En LIDAR baseret MPC regulering er bedre end en linear MPC, mens den ikke kræver væsentlig mere regnekraft. En tredje type regulering er baseret på robust MPC regulering. Generelt er disse meget krævende mht. regnekraft. I afhandlingen er der undersøgt approksimationer, der resulterer i robuste MPC regulatorer, som ikke er så krævende mht. regnekraft.Efter en kort introduktion om vind energi og vindmøller i kapitel 1 er der i kapitel 2 givet en kort beskrivelse af modeller for vindmøller. Kapitel 3 vedrører forskellige metoder til design af regulatorer. Målsætningen med dette kapitel er at give en kort indføring, hvordan forskellige reguleringsformer kan vælges. De efterfølgende 9 kapitler udgør afhandlingens hoveddel og består af artikler, der er publiceret eller vil blive publiceret. Metoder, der er introduceret i kapitel 3, er gennemgået i detaljer her.In the 1970s the oil price crisis encouraged investigation of non-petroleum energy sources of which wind energy was the most promising one. Lately global warming concerns have even intensified the demand for green and sustainable energy resources and opened up several lines of research in this area. Wind turbines are the most common wind energy conversion systems and are hoped to be able to compete economically with fossil fuel power plants in near future. However this demands better technology to reduce the price of electricity production. Control can play an essential part in this context. This is because, on the one hand, control methods can decrease the cost of energy by keeping the turbine close to its maximum efficiency. On the other hand, they can reduce structural fatigue and therefore increase the lifetime of the wind turbine.The power produced by a wind turbine is proportional to the square of its rotor radius, therefore it seems reasonable to increase the size of the wind turbine in order to capture more power. However as the size increases, the mass of the blades increases by cube of the rotor size. This means in order to keep structural feasibility and mass of the whole structure reasonable, the ratio of mass to size should be reduced. This trend results in more flexible structures.Control of the flexible structure of a wind turbine in a wind field with stochastic nature is very challenging. In this thesis we are examining a number of robust model based methods for wind turbine control. Firstly we examine potentials of -synthesis methods and use -tools to analyze robustness of the resulting controllers both in terms of robust stability and robust performance. Afterwards we employ model predictive control (MPC) and show that the way MPC solves control problems suits wind turbine control problems very well, especially when we have preview measurements of wind speed using LIDARs. For the control problem with LIDAR measurements we have proposed a new MPC approach which gives better results than linear MPC while it has almost the same computational complexity. We have also tackled wind turbine control using robust MPC. In general, robust MPC problems are very computationally demanding, however we have shown that with some approximations the resulting robust MPC problem can be specialized with reduced computational complexity.After a short introduction on wind energy and wind turbines in chapter 1, we briefly explain wind turbine modeling in chapter 2. Introductions to different control design methods are given in chapter 3. The goal of this chapter is to show how different control methods are chosen. The next eight chapters comprise the body of the thesis and are scientific papers that are published or going to be published. Control methods which were briefly introduced in chapter 3 are explained in these chapters in details

Online Research Database In Technology

Wind Turbine Control: Robust Model Based Approach

http://orbit.dtu.dk/ws/files/54089598/phd281_Mirzaei_M.pdf

Wind Turbine Control: Robust Model Based Approach

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