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Blade force measurements and electrical torque ripple of a vertical axis wind turbine
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0001-5467-4527
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Wind power has become an attractive alternative for clean energy production. Horizontal axis turbines are increasing in power rating and are maturing as products. The cost of maintenance, noise levels and durability are possible concerns of the modern horizontal axis wind turbines. The vertical axis wind turbine project at Uppsala University addresses these issues among others. The concept removes the need for any yaw or pitch mechanism. Even the gearbox is excluded with the use of a directly driven multi-pole permanent magnet generator. Additionally, the generator and power electronics is placed at ground level. The project has resulted in several open site prototypes of which a 12kW and 200 kW turbine are still subject to active research.

One major disadvantage of vertical axis wind turbines are the oscillating forces acting on the turbine. The first part of this work presents a measurement system developed to capture the forces acting on a blade during operation of the 12 kW prototype. The systems performance and data output is presented and thorough error estimations has been performed.

In modern turbines it is common to have the generator power rectified into a DC-voltage, feeding an inverter connected to the grid. The rectifier is usually also an inverter allowing full control of the generator and the DC-link voltage. In the concept used on the 12 kW prototype, the electric power of the generator is instead passively rectified using diodes to produce the DC-voltage. Diodes are considered a cheap and robust solution for producing the DC-voltage. However, one drawback is the high current ripples produced. The current ripples lead to an electric torque ripple. This work studies how this electric torque ripple translates into a mechanical torque ripple on the turbine. A simulation model is developed and the results are compared with the force measurements on the 12 kW prototype.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2016.
Series
UURIE / Uppsala University, Department of Engineering Sciences, ISSN 0349-8352 ; 346-16L
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-272342OAI: oai:DiVA.org:uu-272342DiVA: diva2:893812
Presentation
2016-02-10, Å4101, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2016-01-13 Created: 2016-01-13 Last updated: 2016-01-13Bibliographically approved
List of papers
1. Evaluation of a Blade Force Measurement System for a Vertical Axis Wind Turbine Using Load Cells
Open this publication in new window or tab >>Evaluation of a Blade Force Measurement System for a Vertical Axis Wind Turbine Using Load Cells
Show others...
2015 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 6, 5973-5996 p.Article in journal (Refereed) Published
Abstract [en]

Unique blade force measurements on an open site straight-bladed vertical axis wind turbine have been performed. This paper presents a method for measuring the tangential and normal forces on a 12-kW vertical axis wind turbine prototype with a three-bladed H-rotor. Four single-axis load cells were installed in-between the hub and the support arms on one of the blades. The experimental setup, the measurement principle, together with the necessary control and measurement system are described. The maximum errors of the forces and accompanying weather data that can be obtained with the system are carefully estimated. Measured forces from the four load cells are presented, as well as the normal and tangential forces derived from them and a comparison with theoretical data. The measured torque and bending moment are also provided. The influence of the load cells on the turbine dynamics has also been evaluated. For the aerodynamic normal force, the system provides periodic data in agreement with simulations. Unexpected mechanical oscillations are present in the tangential force, introduced by the turbine dynamics. The measurement errors are of an acceptable size and often depend on the measured variable. Equations are presented for the calculation of measurement errors.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-260148 (URN)10.3390/en8065973 (DOI)000357489700067 ()
Funder
StandUpStandUp for Wind
Available from: 2015-08-17 Created: 2015-08-17 Last updated: 2017-12-04
2. Measurements of the Aerodynamic Normal Forces on a 12-kW Straight-Bladed Vertical Axis Wind Turbine
Open this publication in new window or tab >>Measurements of the Aerodynamic Normal Forces on a 12-kW Straight-Bladed Vertical Axis Wind Turbine
2015 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 8Article in journal (Refereed) Published
Abstract [en]

The knowledge of unsteady forces is necessary when designing vertical axis wind turbines (VAWTs). Measurement data for turbines operating at an open site are still very limited. The data obtained from wind tunnels or towing tanks can be used, but have limited applicability when designing large-scale VAWTs. This study presents experimental data on the normal forces of a 12-kW straight-bladed VAWT operated at an open site north of Uppsala, Sweden. The normal forces are measured with four single-axis load cells. The data are obtained for a wide range of tip speed ratios: from 1.7 to 4.6. The behavior of the normal forces is analyzed. The presented data can be used in validations of aerodynamic models and the mechanical design for VAWTs.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-260569 (URN)10.3390/en8088482 (DOI)000360586600052 ()
Available from: 2015-08-20 Created: 2015-08-20 Last updated: 2017-12-04Bibliographically approved
3. Mechanical torque ripple from a passive diode rectifier in a 12 kW vertical axis wind turbine
Open this publication in new window or tab >>Mechanical torque ripple from a passive diode rectifier in a 12 kW vertical axis wind turbine
2017 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 32, no 1, 164-171 p.Article in journal (Refereed) Published
Abstract [en]

The influence of passive rectification on the mechanical torque of a permanent magnet generator for a directly driven vertical axis wind turbine has been studied. Passive diode rectification introduce electromagnetic torque ripple from the generator. The conversion of electromagnetic torque ripple into mechanical torque ripple and rotational speed ripple has been modeled, analytically evaluated, and simulated. The simulations have been compared to measurements on an open site 12 kW prototype. A parameter study with the model illustrates the impact of shaft torsional spring constant, generator rotor inertia, generator inductance, and dc-link capacitance. The results show that the shaft and generator rotor can be an effective filter of electromagnetic torque ripple from diode rectification. The measured mechanical torque ripple amplitude on the prototype is less than +/- 0.9% of nominal turbine torque. The measurements compare well with the simulations.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-272363 (URN)10.1109/TEC.2016.2626783 (DOI)000396130300016 ()
Available from: 2016-01-13 Created: 2016-01-13 Last updated: 2017-10-18Bibliographically approved

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