Angelou, Nikolas

Engholm Pedersen, Jens

Harris, Michael

Mikkelsen, Torben

Montes, Belen Fernández

Pedersen, Anders Tegtmeier

Sjöholm, Mikael

Slinger, Chris

IntroductionIn recent years the use of wind lidars mounted directly on wind turbines has received increasing attention, and such systems are becoming commercially available. One aim of turbine-mounted wind lidars is to use them for prevision in connection with advanced feed-forward control systems for load reduction and power optimization. To date, main attention has been on control schemes where measurements of wind speeds and direction upwind are used for yaw and speed corrections. In this study we investigate experimentally the feasibility of using lidars integrated in the turbine blades for alleviating loads and also for active individual pitch control.ApproachTwo small telescope units with 1” optics were mounted on either side of one blade of a Vestas NM80 turbine, 15 m from the spinner and connected through fibre optical cables to a modified ZephIR 300 continuous-wave Doppler lidar from Natural Power, UK. The ZephIR was installed in the tip of the spinner of the turbine. The two telescopes’ line-of-sights were converging with 10 angle, resulting in an intersection at 5 m in front of the blade along the cord extension line. By using an optical switch, the line-of-sight wind speeds could be measured alternately from the two telescopes.Main body of abstractThe two telescope blade lidar system was installed in the turbine in the summer of 2012 and the following measurement campaign ran from July 13 through August 19. At the same time a spinner lidar intended for measuring the inflow in a two-dimensional plane upwind was installed in the turbine and the first results from these experiments will be presented in another EWEA 2013 contribution. The lidar logged the raw Doppler spectra and the wind speed estimation was done subsequently using software designed specifically for the blade-mounted lidar. Simultaneously, data regarding wind speed, rotational speed, and pitch angle recorded by the turbine was logged as well as data from a nearby met mast. The encouraging results of this first campaign include wind speed measurements at 20 Hz data rate along the rotor plane, acquired during the co-rotation of the telescopes and the wind turbine blade. Because of the placement 15 m down the blade the measured speeds are high, typically in excess of 25 m/s. However, the lidar can measure up to about 40 m/s and has no difficulties measuring the required speeds. In addition to providing interesting information about the wind very close to the blade, the measurements were further used for assessing the blade angle-of-attack (AOA) as function of the turbine rotation. This showed that even for the pitch-regulated turbine the AOA could be several degrees away from perfect pitch because of the different wind speeds in the top and bottom of the rotor plane. ConclusionWe present here what we believe is the first successful wind speed measurements from a dual-telescope lidar installed on the blade of an operating wind turbine. The full-scale field test performed in the summer of 2012 has clearly demonstrated the possibility of integrating lidar telescopes into turbine blades as well as the capability of the lidar to measure the required wind speeds and to operate in the challenging environment of a rotating spinner and vibrating blade. The use of two separate telescopes allows a direct measurement of the blade’s AOA demonstrating its potential use in future advanced control systems.<br/

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Downloaded from orbit.dtu.dk on: Dec 20, 2017Full-Scale Field Test of a Blade-Integrated Dual-Telescope Wind LidarPedersen, Anders Tegtmeier; Sjöholm, Mikael; Angelou, Nikolas; Mikkelsen, Torben Krogh; Montes,Belen Fernández; Engholm Pedersen, Jens; Slinger, Chris; Harris, MichaelPublication date:2013Link back to DTU OrbitCitation (APA):Pedersen, A. T., Sjöholm, M., Angelou, N., Mikkelsen, T., Montes, B. F., Engholm Pedersen, J., ... Harris, M.(2013). Full-Scale Field Test of a Blade-Integrated Dual-Telescope Wind Lidar. Poster session presented atEuropean Wind Energy Conference & Exhibition 2013, Vienna, Austria.Steen Andreasen (IPU, Lyngby, Denmark) is gratefully acknowledged for the mechanical design of the 2D scanhead / the blade lidar telescopes. Karen Enevoldsen, Per Hansen, Kasper Hjorth Hansen and Claus Brian MunkPedersen (DTU Wind Energy) are gratefully acknowledged for their skilled assistance with communicationsoftware and remote control. Lars Christensen and Michael Rasmussen (DTU Wind Energy) are gratefullyacknowledged for their assistance with installation of the lidars in the NM80 test turbine. Dong Energy (Denmark)is gratefully acknowledged for providing access to the NM 80 test turbine at Tjæreborg Enge during the test periodssummer and autumn 2012. Vestas Service team is acknowledged for safe control and operation of the NM80 testturbine during the experimental demonstration period.The technology has been developed as part of the Danish research infrastructure facility activities under theauspices of WindScanner.dk. Danish Agency for Science, Technology and Innovation, Research Infrastructure2009 Grant No. 2136-08-0022 and the project was financially supported by the Danish Advanced TechnologyFoundation: Grant 049-2009-3: “Integration of Wind LIDAR’s In Wind Turbines for Improved Productivity andControl”.1. Pedersen, A. T., Montes, B. F., Pedersen. J. E., Harris, M., Mikkelsen, T., Demonstration of short-range wind lidar in high-performance wind tunnel, EWEA 2012, PO.78, 2012 2. http://www.zephirlidar.comFull-Scale Field Test of a Blade-IntegratedDual-Telescope Wind Lidar Anders Tegtmeier Pedersen1, Mikael Sjöholm1, Nikolas Angelou1, Torben Mikkelsen1,Belen Fernández Montes2, Jens Engholm Pedersen3, Chris Slinger4, and Michael Harris41DTU Wind Energy, 2LM Wind Power, 3NKT Photonics, 4ZephIR LidarPO. ID166ResultsIntroductionConclusionsMounting of lidarReferences             EWEA 2013, Vienna, Austria: Europe’s Premier Wind Energy EventThe dual-telescope wind lidar consists of two small telescope units with 1” opticsconnected to a modified ZephIR 300 continuous-wave Doppler lidar1,2 through fibreoptic cables. The ZephIR lidar is installed in the spinner of a Vestas NM80 turbineand the telescopes are mounted on either side of one of the blades 16.2 m from thecentre of rotation. The two telescopes’ beam axes are converging with approximately10 angle, resulting in an intersection at 5 m in front of the blade along the cordextension line where also the focus of the laser beams lie. By using an opticalswitch, operating at a switch rate of 10 Hz, the line-of-sight wind speeds can bemeasured alternately from the two telescopes.We present here what we believe are the first successful wind speed measurements from a dual-telescopelidar installed on the blade of an operating wind turbine. The results show a variation in AOA as the bladescut through the shear profile. The full-scale field test performed in the summer of 2012 has clearlydemonstrated the possibility of integrating lidar telescopes into turbine blades as well as the capability of thelidar to measure the required wind speeds and to operate in the challenging environment of a rotatingspinner and vibrating blade. The use of two separate telescopes allows a direct measurement of the blade’sAOA demonstrating its potential use in future advanced control systems.Figure 3. Angle-of-attack (AOA)calculated from the speedmeasurements shown above. Inthe beginning of the time seriesthe AOA oscillates around 5 andincreases to around 7 in the end.An oscillation with the samefrequency as above can be seen,although also some noise ispresent. Missing data points areseen to appear where the groundsignal filter has removed the windsignal from telescope T2. Thishighlights the importance of highdata availability.AcknowledgementsIn recent years the use of wind lidars mounteddirectly on wind turbines has receivedincreasing attention. One aim of turbine-mounted wind lidars is to use them forprevision in connection with advanced feed-forward control systems for load reduction andpower optimization. To date, main attentionhas been on control schemes wheremeasurements of wind speeds and directionupwind are used for yaw and speedoptimization.In this study we experimentally investigate thefeasibility of using lidars integrated in theturbine blades for alleviating loads and also foractive individual pitch control. Themeasurement campaign ran from July 13through August 24 2012. At the same time aspinner lidar intended for measuring the inflowin a two-dimensional plane upwind wasinstalled in the turbine and the first resultsfrom these experiments will be presented inanother EWEA 2013 contribution (PO. ID 126).Figure 2. Time series of the speedmeasured by the two telescopesover a one minute period. Themeasured speeds are seen tooscillate in excellent agreementwith each other and also with therotation period of the turbine. Thepeaks in wind speed coincide withmeasurement at the highest pointof the rotation, where the windspeed is highest due to shear.Also noticed is a band between18.0 m/s and 18.5 m/s where nomeasurements were obtained byTelescope 2. This is due to windsignals coinciding with groundsignals and these are thereforefiltered out.Figure 1. Example of a normalisedDoppler spectrum obtained bytelescope T1. The spectrum isseen to contain two distinct peakslocated at 24.4 MHz and 25.2MHz, respectively. The first peakis due to reflections from theground when the telescope ispointing downwards and if notfiltered out this can lead toerroneous wind speedestimations. The second peak isthe wind signal which is thecombined effect of the wind andthe motion of the blade.

Full-Scale Field Test of a Blade-Integrated Dual-Telescope Wind Lidar

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Full-Scale Field Test of a Blade-Integrated Dual-Telescope Wind Lidar

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