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Experimental Verification of a Back-to-Back 2L-3L Grid Connection System for a Marine Current Energy Converter
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.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Rivers, tides and other ocean currents are renewable energy sources with great potential across the globe.A research group at Uppsala University is working on converting the power in rivers and ocean tidesusing a vertical axis turbine with a directly driven permanent magnet generator. The concept in focususes an omnidirectional, fixed pitch vertical axis turbine directly connected to a permanent magnetgenerator. Few moving parts and an overall low mechanical complexity is the main idea behind theconcept. A first full prototype was deployed in 2013 in the river Dalälven in the town of Söderfors. Thework presented here is a step towards grid connection of the marine current energy converter prototype.A back-to-back 2L-3L grid connection topology has been proposed. The system is adapted to the scaledprototype but is intended for larger turbines. The proposed grid connection system utilizes a three-levelcascaded H-Bridge voltage source converter (3L-CHBVSC) on the grid side together with a well knowtwo-level voltage source converter on the generator side. The use of a multilevel converter brings severaladvantages such as higher efficiency, more sinusoidal voltages and currents and smaller grid filtersamong other advantages. The proposed grid connection system has been constructed in the laboratory.The work presented here aims to evaluate the system in the laboratory. A synchronous generator with avery similar design to the on-site generator is used for the tests. The generator, driven by an inductionmotor, is connected to the system and power is successfully transferred to the grid. The conducted testsare used to verify the functionality of the system before installation at the research site.

Place, publisher, year, edition, pages
2016. 294-299 p.
Keyword [en]
marine current energy converter, grid connection, three-level cascaded H-bridge
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-304658OAI: oai:DiVA.org:uu-304658DiVA: diva2:1033384
Conference
2nd International Conference on Offshore Renewable Energy (CORE2016), Glasgow, UK, Sep. 12-14, 2016.
Projects
Marine Current Power
Available from: 2016-10-06 Created: 2016-10-06 Last updated: 2016-10-12
In thesis
1. Grid Connection of Permanent Magnet Generator Based Renewable Energy Systems
Open this publication in new window or tab >>Grid Connection of Permanent Magnet Generator Based Renewable Energy Systems
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Renewable energy is harnessed from continuously replenishing natural processes. Some commonly known are sunlight, water, wind, tides, geothermal heat and various forms of biomass. The focus on renewable energy has over the past few decades intensified greatly. This thesis contributes to the research on developing renewable energy technologies, within the wind power, wave power and marine current power projects at the division of Electricity, Uppsala University. In this thesis grid connection of permanent magnet generator based renewable energy sources is evaluated.

A tap transformer based grid connection system has been constructed and experimentally evaluated for a vertical axis wind turbine. Full range variable speed operation of the turbine is enabled by using the different step-up ratios of a tap transformer. This removes the need for a DC/DC step or an active rectifier on the generator side of the full frequency converter and thereby reduces system complexity. Experiments and simulations of the system for variable speed operation are done and efficiency and harmonic content are evaluated. 

The work presented in the thesis has also contributed to the design, construction and evaluation of a full-scale offshore marine substation for wave power intended to grid connect a farm of wave energy converters. The function of the marine substation has been experimentally tested and the substation is ready for deployment. Results from the system verification are presented. Special focus is on the transformer losses and transformer in-rush currents.

A control and grid connection system for a vertical axis marine current energy converter has been designed and constructed. The grid connection is done with a back-to-back 2L-3L system with a three level cascaded H-bridge converter grid side. The system has been tested in the laboratory and is ready to be installed at the experimental site. Results from the laboratory testing of the system are presented.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 79 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1436
Keyword
VAWT, H-rotor, Tap Transformer, Cascaded H-bridge Multi-Level, Renewable Energy, Wind power, Wave power, Marine Current Power
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-304659 (URN)978-91-554-9712-5 (ISBN)
Public defence
2016-11-25, Polhemsalen, 10134, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Projects
Wind PowerWave PowerMarine Currnet Power
Available from: 2016-11-03 Created: 2016-10-06 Last updated: 2016-11-16Bibliographically approved

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