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Mechanical torque ripple from a passive diode rectifier in a 12 kW vertical axis wind turbine
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0001-5467-4527
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0001-8598-2565
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.

Place, publisher, year, edition, pages
2017. Vol. 32, no 1, 164-171 p.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-272363DOI: 10.1109/TEC.2016.2626783ISI: 000396130300016OAI: oai:DiVA.org:uu-272363DiVA: diva2:893811
Available from: 2016-01-13 Created: 2016-01-13 Last updated: 2017-10-18Bibliographically approved
In thesis
1. Blade force measurements and electrical torque ripple of a vertical axis wind turbine
Open this publication in new window or tab >>Blade force measurements and electrical torque ripple of a vertical axis wind turbine
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:nbn:se:uu:diva-272342 (URN)
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
2. 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. 81 p.
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: 2017-11-14

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Rossander, MorganGoude, AndersEriksson, Sandra

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