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Grid Integration and Impact of a Wave Power System
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Wave Energy)
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing energy consumption and concern for carbon emissions has boosted the demand for renewable energy production. The focus on renewable energy has gained much attention in wind, solar, hydro and wave power generations. Wave power has great potential due to its high energy density but there are challenges as well. This thesis addresses some of the challenges involved in the grid integration of wave energy and in maintaining power quality. In this thesis a grid connection of permanent magnet linear generator (PMLG) based wave energy converter (WEC) as a renewable energy source is evaluated at the Division of Electricity, Uppsala University.

The grid impact of a wave energy park in terms of flicker, voltage variations and harmonic distortion at the grid-connection point are investigated extensively. The short-term flicker level generated by the WEC and a wave energy park (WEP) related to the rated WEP power and grid impedance angle at the PCC are evaluated.

In this thesis, an improved control for hybrid energy storage is presented, which enhanced the efficiency and increased the battery life while smoothing the intermittent power from the WEP. The thesis, also, contributes to resolve the problem of inertia and power balance by integrating the DC-link capacitor in the control loop which reduce the size and cost of the components at the DC-link.

The work presented in the thesis has contributed for the force control of the PMLG which is predicted and controlled by regulating the stator currents of the generator. A nonlinear, neural, control is evaluated and compared to a linear, proportional-integral, control. The results from the nonlinear control show the good agreement between the referenced and the generated currents. The reduced losses enhanced the accuracy of the system.

A control and grid connection system for a WEC has been designed and installed. The thesis addresses the issue of power quality in low, steady and varying power flows of compliance with the grid code requirements.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 116
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1842
Keywords [en]
ANN, buck-boost converter, current control, energy storage system, force control, flicker, FPGA control, grid integartion, harmonics, linear generator, PHIL, microgrid, voltage variation, wave energy, WEC
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-390133ISBN: 978-91-513-0725-1 (print)OAI: oai:DiVA.org:uu-390133DiVA, id: diva2:1343961
Public defence
2019-10-04, 80127, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2015-03126
Note

We havn't got the response from the opponent yet, It will be confirmed in a few days.

Available from: 2019-09-13 Created: 2019-08-19 Last updated: 2019-10-15
List of papers
1. Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
Open this publication in new window or tab >>Wave Energy Research at Uppsala University and The Lysekil Research Site, Sweden: A Status Update
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2015 (English)Conference paper, Published paper (Refereed)
Abstract [en]

This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.

Keywords
Wave energy, point absorber, experiments, arrays, generators, ROVs
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Ocean and River Engineering
Identifiers
urn:nbn:se:uu:diva-265218 (URN)
Conference
Proceedings of the 11th European Wave and Tidal Energy Conference. Nantes, France, September 2015
Available from: 2015-10-26 Created: 2015-10-26 Last updated: 2019-08-19Bibliographically approved
2. A Comparative Analysis of Linear and Nonlinear Control of Wave Energy Converter for a Force Control Application
Open this publication in new window or tab >>A Comparative Analysis of Linear and Nonlinear Control of Wave Energy Converter for a Force Control Application
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(English)In: International Marine Energy Journal, ISSN 2631-5548Article in journal (Refereed) Submitted
Abstract [en]

The aim of wave energy converters (WECs) is to harvest the energy from the ocean waves and convert into electricity. Optimizing the generator output is a vital point of research. A WEC behaves as a nonlinear system in real ocean waves and a control that approximates the behaviour of the system is required. In order to predict the behaviour of WEC, a controller is implemented with an aim to track the referenced trajectory for a force control application of the WEC. A neural model is implemented for the system identification and control of the nonlinear process with a neural nonlinear autoregressive moving average exogenous (NARMAX) model. The neural model updates the weights to reduce the error by using the Levenberg-Marquardt back-propagation algorithm for a single-input-single-output (SISO) nonlinear system. The performance of the system under the proposed scheme is compared to the same system under a PI-controller scheme, where the PI gains have been tuned accordingly, to verify the control capacity of the proposed controller. The results show a good tracking of dq (direct-quadrature) axes currents by regulating the stator currents, and hence a force control is achieved at different positions of the translator. The dynamic performance of the control is verified in a time domain analysis for the displacement of the translator.

Place, publisher, year, edition, pages
Southampton, UK: International Marine Energy Journal
Keywords
current control, force control, neural NARMAX, permanent magnet linear generator (PMLG), wave energy converter
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering with specialization in Automatic Control
Identifiers
urn:nbn:se:uu:diva-390099 (URN)
Funder
Swedish Research Council, 2015-03126StandUp
Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-19
3. Power Hardware in-the-Loop Real Time Modelling using Hydrodynamic Model of a Wave Energy Converter with Linear generator Power Take-Off
Open this publication in new window or tab >>Power Hardware in-the-Loop Real Time Modelling using Hydrodynamic Model of a Wave Energy Converter with Linear generator Power Take-Off
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2019 (English)In: the 29th International Ocean and Polar Engineering Conference (ISOPE), Honolulu, Hawaii, USA, June 16-21, 2019, 2019Conference paper, Oral presentation with published abstract (Refereed)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-390101 (URN)
Conference
29th International Ocean and Polar Engineering Conference (ISOPE)
Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-19
4. Energy management for a grid-connected wave energy park through a hybrid energy storage system
Open this publication in new window or tab >>Energy management for a grid-connected wave energy park through a hybrid energy storage system
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2018 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 231, p. 399-411Article in journal (Refereed) Published
Abstract [en]

The concern for climate change and energy consumption has increased the demand for renewable energy production considerably. Marine energy sources attract attention because of their high energy density. Wave energy is an attractive renewable energy source with large potential. Due to the nature of the ocean waves, a linear wave energy converter generates intermittent power. It is therefore crucial to regularize the power before connecting to the grid. Energy storage systems present effective ways to minimize the power fluctuations and deliver a steady power to the grid. In this paper, we present an energy management control system with a dynamic rate limiter. The method is applied to control a hybrid energy storage system, combining battery and supercapacitor, with a fully active topology controlled by the power converters. The results show that the method is able to control the charging and discharging states of the battery and the supercapacitor, and minimize the power fluctuation to the grid. The algorithm ensures low losses by shifting the required power and the stored power smoothly over the energy storage system.

Keywords
Wave energy converter, Hybrid energy storage system, Energy management control system, Dynamic rate limiter, State of charge
National Category
Energy Systems
Identifiers
urn:nbn:se:uu:diva-361207 (URN)10.1016/j.apenergy.2018.09.146 (DOI)000452345400030 ()
Funder
StandUpSwedish Research Council, 2015-03126Carl Tryggers foundation
Available from: 2018-09-21 Created: 2018-09-21 Last updated: 2019-08-19Bibliographically approved
5. Virtual Synchronous Generator Based Current Synchronous Detection Scheme for a Virtual Inertia Emulation in SmartGrids
Open this publication in new window or tab >>Virtual Synchronous Generator Based Current Synchronous Detection Scheme for a Virtual Inertia Emulation in SmartGrids
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2019 (English)In: Energy and Power Engineering, ISSN 1949-243X, E-ISSN 1947-3818, Vol. 11, no 3, p. 99-131Article in journal (Refereed) Published
Abstract [en]

Renewable energy sources, such as photovoltaicwind turbines, and wave power converters, use power converters to connect to the grid which causes a loss in rotational inertia. The attempt to meet the increasing energy demand means that the interest for the integration of renewable energy sources in the existing power system is growing, but such integration poses challenges to the operating stability. Power converters play a major role in the evolution of power system towards SmartGrids, by regulating as virtual synchronous ge-nerators. The concept of virtual synchronous generators requires an energy storage system with power converters to emulate virtual inertia similar to the dynamics of traditional synchronous generators. In this paper, a dynamic droop control for the estimation of fundamental reference sources is imple-mented in the control loop of the converter, including active and reactive power components acting as a mechanical input to the virtual synchronous generator and the virtual excitation controller. An inertia coefficient and a droop coefficient are implemented in the control loop. The proposed con-troller uses a current synchronous detection scheme to emulate a virtual iner-tia from the virtual synchronous generators. In this study, a wave energy converter as the power source is used and a power management of virtual synchronous generators to control the frequency deviation and the terminal voltage is implemented. The dynamic control scheme based on a current synchronous detection scheme is presented in detail with a power manage-ment control. Finally, we carried out numerical simulations and verified the scheme through the experimental results in a microgrid structure.

Place, publisher, year, edition, pages
Scientific Research Publishing, 2019
Keywords
Dynamic Droop Control, Energy Storage, Virtual Inertia, Virtual Synchronous Generator
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-379215 (URN)10.4236/epe.2019.113007 (DOI)
Funder
Swedish Research Council, 2015-03126StandUp
Available from: 2019-03-13 Created: 2019-03-13 Last updated: 2019-08-19Bibliographically approved
6. Power Hardware-in-the-loop simulations of Grid-Integration of a Wave Power Park
Open this publication in new window or tab >>Power Hardware-in-the-loop simulations of Grid-Integration of a Wave Power Park
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2019 (English)In: 13th European Wave and Tidal Energy Conference (EWTEC), Napoli, Italy, September 1-6, 2019, Napoli, Italy, 2019Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Napoli, Italy: , 2019
Keywords
energy storage system, grid integration, hardware-in-the-loop, microgrid, power fluctuations, wave energy converter
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-390104 (URN)
Conference
13th European Wave and Tidal Energy Conference (EWTEC), Napoli, Italy, September 1-6, 2019
Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-19
7. Power Control Strategies for a Smoother Power Output from a Wave Power Plant
Open this publication in new window or tab >>Power Control Strategies for a Smoother Power Output from a Wave Power Plant
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2019 (English)In: 13th European Wave and Tidal Energy Conference (EWTEC), Napoli, Italy, September 1-6, 2019, Napoli, Italy: European Wave and Tidal Energy Conference , 2019Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Napoli, Italy: European Wave and Tidal Energy Conference, 2019
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-390134 (URN)
Conference
European Wave and Tidal Energy Conference (EWTEC)
Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-19
8. Grid Integration and a Power Quality Assessment of a Wave Energy Park
Open this publication in new window or tab >>Grid Integration and a Power Quality Assessment of a Wave Energy Park
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2019 (English)In: IET Smart Grid, ISSN 2515-2947, p. 1-14Article in journal (Refereed) Published
Abstract [en]

This paper presents a step towards the grid connection of a wave energy park through an electric power conversion system(EPCS)developed and installed for the wave energy harvesting in Lysekil, Sweden.TheEPCScomprises ofa rectifier,aDC-bus,andan inverterfollowedbyaharmonic filter. The higher and lowerorder harmonics injected bythe inverterin a power quality contextare investigated. The lowerorder voltage harmonics partially distort the voltage sourceinverter(VSI)outputgridcurrent.Aphase-lockedloop(PLL)basedgridphasetrackingisusedtoattenuatethelowerorder harmonicsbyreflectingthegridharmonicsintheinverteroutput.Anexpressionforthegridcurrentharmonicsasafunctionofthe gridvoltageharmonicshasbeenderived and implemented. AmathematicalmodelisderivedtoobtainatransferfunctionforthePLLand finally,PI-gainsaretunedforastablesystemoperation.Aharmonicfilterfor mitigatingthehigherorderharmonicshas beenimplemented. The total harmonic distortion (THD) is evaluated experimentally and theresults fulfill the gridcoderequirementsat various frequencies and harmonic orders.

Place, publisher, year, edition, pages
UK: , 2019
Keywords
WAVE ENERGY SMART GRID HARMONIC DISTORTION
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-389779 (URN)10.1049/iet-stg.2019.0009 (DOI)
Funder
Swedish Research Council, 2015-03126
Available from: 2019-07-25 Created: 2019-07-25 Last updated: 2019-08-19
9. Experimental Test of Grid Connected VSC to Improve the Power Quality in a Wave Power System
Open this publication in new window or tab >>Experimental Test of Grid Connected VSC to Improve the Power Quality in a Wave Power System
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2018 (English)Conference paper, Published paper (Refereed)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-361208 (URN)
Conference
Fifth International Conference on Electric Power and Energy Conversion Systems (EPECS 2018), Kitakyushu, Japan : April 23-25, 2018
Available from: 2018-09-21 Created: 2018-09-21 Last updated: 2019-08-19Bibliographically approved
10. Grid Impact and Power quality Assessment in wave Energy Parks: Different layouts and Power Penetrations using Energy Storage
Open this publication in new window or tab >>Grid Impact and Power quality Assessment in wave Energy Parks: Different layouts and Power Penetrations using Energy Storage
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(English)In: IET Electric Power Applications, ISSN 1751-8660, E-ISSN 1751-8679, ISSN 1751-8679Article in journal (Refereed) Submitted
Place, publisher, year, edition, pages
UK: Institution of Engineering and Technology
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-390136 (URN)
Funder
Swedish Research Council, 2015-03126StandUp
Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-19

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