Development of Multirate Model and Analysis of Applicability to Wind Turbine Digital Fluid Power Transmissions
Authors
Lindberg, Tom-Erik ; Nielsen, Kasper Giøe Brusendorff ; Junker, Peter Moos
Term
4. term
Education
Publication year
2017
Pages
221
Abstract
Digitale hydrauliske transmissioner (DFPT) er et lovende alternativ til drivlinjer baseret på gearkasser og effektelektronik. En vigtig anvendelse er offshore-vindmøller, hvor hydraulikkens høje pålidelighed og robusthed er eftertragtet. En DFPT består af en digital forskydningspumpe og -motor forbundet via fælles trykledninger og udgør dermed selve transmissionen. Pumpe og motor ændrer deres forskydning ved et antal faste akselpositioner. Ved variabel hastighed betyder det, at styringsopdateringerne kommer på forskellige tidspunkter og ikke er synkrone, hvilket skaber et multirate-styringsproblem (forskellige opdateringsrater). For at opnå en lineær kontrolmodel omsættes dynamikken til det spatiale domæne, dvs. beskrevet i forhold til akselposition frem for tid. Herefter afledes en ny multirate-modelleringsteknik ved at kombinere to eksisterende multirate-metoder. Med denne teknik modelleres DFPT lineært, og muligheden for at anvende konventionelle kontrol- og analyseværktøjer vurderes. Resultaterne viser, at multirate-modellering og -styring af en DFPT er mulig både i tidsdomænet og i det spatiale domæne, men at implementering i tidsdomænet af en kontrollov designet i det spatiale domæne ikke er ligetil.
Digital fluid power transmissions (DFPTs) are a promising alternative to drivetrains that rely on gearboxes and power electronics. They are particularly attractive for offshore wind turbines because hydraulic systems are robust and reliable. A DFPT consists of a digital displacement pump and motor connected by shared pressure lines, forming the transmission. The pump and motor change their displacement at a fixed set of shaft positions. Under variable-speed operation, this means control updates happen at irregular times and are not synchronized, creating a multirate control problem with different update rates. To obtain a linear control model, the system dynamics are expressed in the spatial domain, that is, as a function of shaft position rather than time. A new multirate modeling technique is then derived by combining two existing multirate methods. Using this technique, the DFPT is modeled linearly, and the applicability of standard control and analysis tools is evaluated. The results indicate that multirate modeling and control of a DFPT are feasible in both the time domain and the spatial domain, but implementing in the time domain a control law designed in the spatial domain is not straightforward.
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