Technical Briefs

Evaluating Constant DC-Link Operation of Wave Energy Converter

[+] Author and Article Information
Rickard Ekström

e-mail: riek@angstrom.uu.se

Venugopalan Kurupath

e-mail: venugopalan.kurupath@angstrom.uu.se

Cecilia Boström

e-mail: cecilia.bostrom@angstrom.uu.se

Rafael Waters

e-mail: rafael.waters@angstrom.uu.se

Mats Leijon

e-mail: mats.leijon@angstrom.uu.se
Division of Electricity,
Uppsala University,
Uppsala, Sweden

Contributed by the Dynamic Systems Division of ASME for publication in the Journal of Dynamic Systems, Measurement, and Control. Manuscript received September 14, 2012; final manuscript received June 9, 2013; published online August 30, 2013. Assoc. Editor: Evangelos Papadopoulos.

J. Dyn. Sys., Meas., Control 136(1), 014501 (Aug 30, 2013) (6 pages) Paper No: DS-12-1304; doi: 10.1115/1.4024789 History: Received September 14, 2012; Revised June 09, 2013

A wave energy converter (WEC) based on a linear generator and a point-absorbing buoy has been developed at Uppsala University. Interconnecting an array of WECs in parallel requires a point of common coupling, such as a common dc-bus. The dc voltage level seen by the generator is directly linked to the electromagnetic damping of the generator. A lower dc-level results in a higher damping factor and is important for increased absorption of the wave power. The drawback is increased losses in generator windings and cable resistance. There will be an optimal dc-level for maximum power output. This is a function of not only generator and buoy characteristics, but the current sea state. Experimental results of the full-scale system have been carried out, and used as validation of a simulation model of the system. The model is then used to evaluate how the dc-level seen by the generator influence the power output. The results indicate that higher dc-levels should be used at higher sea states, and power output may vary by up to a factor five depending on which dc-level is chosen.

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Fig. 1

Wave energy converter concept

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Fig. 2

Simulation model layout

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Fig. 3

Circuit diagram of the experimental set-up

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Fig. 4

Launching of the linear generator

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Fig. 6

Translator speed versus voltage envelope

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Fig. 7

Translator speed versus voltage envelope verification

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Fig. 8

Simulated phase voltage versus experimental phase voltage for the same wave

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Fig. 9

Simulated power delivery as a function of dc-level for various Hm0

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Fig. 10

Simulated power delivery at optimal dc-level for various Hm0



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