Performance Oriented Control of Digital Displacement Wind Turbine Transmission
Authors
Kinch, Rasmus ; Hauge, Henrik Felthaus ; Daugbjerg, Nicolai Krøgh
Term
4. term
Education
Publication year
2017
Submitted on
2017-06-01
Pages
209
Abstract
Specialet undersøger brugen af en Digital Fluid Power Transmission (DFPT) i en 5 MW havvindmølle og udvikler styring for at maksimere energihøsten. Først fastlægges mekaniske og elektriske driftskrav. Det betragtede system omfatter en DFPT, en generator og en back-to-back-konverter (to effektelektroniske konvertere, der forbinder generatoren med elnettet). Der opbygges ikke-lineære modeller af alle delsystemer, og der udvikles regulatorer til DFPT’en, generatoren og netsiden af konverteren for at øge energihøsten. Systemets ydeevne evalueres med en vindprofil med middelvind på 8 m/s og sammenlignes med en konventionel NREL-referenceturbinemodel. Det DFPT-baserede system følger tiphastighedsforholdet (forholdet mellem bladspidsens hastighed og vindhastigheden) med en RMS-fejl på 0,06, på niveau med referencen. Til gengæld viser spændingsanalyser af rotorakslen, at DFPT-tilfældet giver cirka 24.000 ekstra spændingscyklusser og dermed større akkumuleret udmattelsesskade end NREL-modellen. En mere detaljeret analyse af den mekaniske struktur er nødvendig for at vurdere den forventede levetid.
This thesis examines using a Digital Fluid Power Transmission (DFPT) in a 5 MW offshore wind turbine and designs control strategies to maximize energy capture. Mechanical and electrical operating requirements are identified. The drivetrain includes a DFPT, an electrical generator, and a back-to-back converter (two power converters linking the generator to the grid). Nonlinear models of all subsystems are developed, and controllers are designed for the DFPT, the generator, and the grid side of the converter to increase energy capture. Performance is evaluated with a wind profile with a mean wind speed of 8 m/s and compared with a conventional NREL reference turbine model. The DFPT-based system tracks the tip-speed ratio (the ratio of blade-tip speed to wind speed) with an RMS error of 0.06, comparable to the reference. However, rotor shaft stress analysis shows the DFPT case introduces about 24,000 additional stress cycles, leading to higher accumulated fatigue damage than the NREL model. A more detailed analysis of the mechanical structure is needed to assess expected lifetime.
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