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Force measurements on a VAWT blade in parked conditions
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0002-6975-1588
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0001-5467-4527
2017 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 12, article id 1954Article in journal (Refereed) Published
Abstract [en]

The forces on a turbine at extreme wind conditions when the turbine is parked is one of the most important design cases for the survivability of a turbine. In this work, the forces on a blade and its support arms have been measured on a 12 kW straight-bladed vertical axis wind turbine at an open site. Two cases are tested: one during electrical braking of the turbine, which allows it to rotate slowly, and one with the turbine mechanically fixed with the leading edge of the blade facing the main wind direction. The force variations with respect to wind direction are investigated, and it is seen that significant variations in forces depend on the wind direction. The measurements show that for the fixed case, when subjected to the same wind speed, the forces are lower when the blade faces the wind direction. The results also show that due to the lower forces at this particular wind direction, the average forces for the fixed blade are notably lower. Hence, it is possible to reduce the forces on a turbine blade, simply by taking the dominating wind direction into account when the turbine is parked. The measurements also show that a positive torque is generated from the blade for most wind directions, which causes the turbine to rotate in the electrically-braked case. These rotations will cause increased fatigue loads on the turbine blade.

Place, publisher, year, edition, pages
2017. Vol. 10, no 12, article id 1954
National Category
Energy Systems
Identifiers
URN: urn:nbn:se:uu:diva-331818DOI: 10.3390/en10121954ISI: 000423156900025OAI: oai:DiVA.org:uu-331818DiVA, id: diva2:1150365
Funder
StandUp for WindStandUp
Available from: 2017-10-18 Created: 2017-10-18 Last updated: 2018-03-23Bibliographically approved
In thesis
1. Electromechanics of Vertical Axis Wind Turbines
Open this publication in new window or tab >>Electromechanics of Vertical Axis Wind Turbines
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wind power is an established mean of clean energy production and the modern horizontal axis wind turbine has become a common sight. The need for maintenance is high and future wind turbines may need to be improved to enable more remote and offshore locations. Vertical axis wind turbines have possible benefits, such as higher reliability, less noise and lower centre of gravity. This thesis focuses on electromechanical interaction in the straight bladed Darrieus rotor (H-rotor) concept studied at Uppsala University.

One of the challenges with vertical axis technology is the oscillating aerodynamic forces. A force measurement setup has been implemented to capture the forces on a three-bladed 12 kW open site prototype. The normal force showed good agreement with simulations. An aerodynamic torque could be estimated from the system. The total electrical torque in the generator was determined from electrical measurements. Both torque estimations lacked the expected aerodynamic ripple at three times per revolution. The even torque detected is an important result and more studies are required to confirm and understand it.

The force measurement was also used to study the loads on the turbine in parked conditions. It was discovered that there is a strong dependence on wind direction and that there is a positive torque on the turbine at stand still. The results can assist to determine the best parking strategies for an H-rotor turbine.

The studied concept also features diode rectification of the voltage from the permanent magnet synchronous generator. Diodes are considered a cheap and robust solution for rectification at the drawback of inducing ripple in the torque and output voltage. The propagation of the torque ripple was measured on the prototype and studied with simulations and analytical expressions. One key conclusion was that the mechanical driveline of the turbine is an effective filter of the diode induced torque ripple.

A critical speed controller was implemented on the prototype. The controller was based on optimal torque control and according to the experiments and the simulations it was able to avoid a rotational speed span. Finally, the optimal torque control was evaluated for multiple turbines with diode rectification to a common DC-link. The setup can potentially reduce the overall complexity of wind farms. The simulations suggest that stability of the system can be obtained by controlling the DC-link load as a semi constant voltage.

The thesis is based on nine papers of which six are treated in the thesis summary.

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 81
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1581
Keyword
Wind power, Diode rectification, Control, Measurement, Simulation, Electromechanical coupling, vindkraft, diodlikriktning, reglering, mätning, simulering
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Energy Systems
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-331844 (URN)978-91-513-0117-4 (ISBN)
Public defence
2017-12-08, Å2005, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
StandUpStandUp for Wind
Available from: 2017-11-14 Created: 2017-10-18 Last updated: 2018-03-07

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Goude, AndersRossander, Morgan

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