| 1. |
- Fjellstedt, Christoffer, et al.
(author)
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A Review of AC and DC Collection Grids for Offshore Renewable Energy with a Qualitative Evaluation for Marine Energy Resources
- 2022
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In: Energies. - : MDPI. - 1996-1073. ; 15:16
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Journal article (peer-reviewed)abstract
- Marine energy resources could be crucial in meeting the increased demand for clean electricity. To enable the use of marine energy resources, developing efficient and durable offshore electrical systems is vital. Currently, there are no large-scale commercial projects with marine energy resources, and the question of how to design such electrical systems is still not settled. A natural starting point in investigating this is to draw on experiences and research from offshore wind power. This article reviews different collection grid topologies and key components for AC and DC grid structures. The review covers aspects such as the type of components, operation and estimated costs of commercially available components. A DC collection grid can be especially suitable for offshore marine energy resources, since the transmission losses are expected to be lower, and the electrical components could possibly be made smaller. Therefore, five DC collection grid topologies are proposed and qualitatively evaluated for marine energy resources using submerged and non-submerged marine energy converters. The properties, advantages and disadvantages of the proposed topologies are discussed, and it is concluded that a suitable electrical system for a marine energy farm will most surely be based on a site-specific techno-economic analysis.
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| 2. |
- Frost, Anna E., 1988-, et al.
(author)
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Power flow in the air gap of linear electrical machines by utilization of the Poynting vector : Part 1 - Analytical expressions
- 2022
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In: The Journal of Engineering. - : Institution of Engineering and Technology (IET). - 2051-3305. ; 2022:4, s. 377-388
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Journal article (peer-reviewed)abstract
- Analytical solutions and estimations for the power flow in the air gap of linear electrical machines of different geometries are derived from Poynting's theorem. The different geometries considered are flat one-sided, multi-sided, and tubular linear electrical machines. The radial power flow for all considered geometries is dependent on the area of the air gap, the electric field, the magnetic field, and the load angle. The tangential power flow for both flat one-sided and tubular linear electrical machines is dependent of the area of the air gap, number of poles, the electric field, the magnetic field, and the load angle. The number of poles could be increased to decrease the tangential power flow in flat linear electrical machines. The expression for the tangential flow in tubular linear electrical machines is so complicated that it is difficult to draw conclusions from it.
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| 3. |
- Potapenko, Tatiana
(author)
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Modelling of Ocean Wave Energy Conversion for Increased Power Absorption
- 2022
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Doctoral thesis (other academic/artistic)abstract
- The Earth is also called the blue planet, because more than 70 % of its surface is covered by water, mainly in oceans and seas. Wind blowing over the oceans is creating water waves, which can travel thousands of kilometers with just a small energy loss. Despite the abundant potential for the green energy market, wave energy is not yet exploited to the extent of wind and solar energies.There have been numerous attempts to convert wave energy into electricity. The wave energy converter, developed at Uppsala University, Sweden is of a point absorber type. The principal idea lies in utilizing a novel linear generator. The translator is a moving part inside the sub-merged linear generator and it is connected to a buoy, floating on the water surface. The buoy moves with the waves and the translator is dragged up and down relative to the stator. This reciprocal motion induces a voltage in the stator windings.The up-to-date stage of development for wave energy converters poses various issues. Still open challenges hold the technology away from commercial energy production. One of the main goals in wave energy research is to enhance the absorbed power for a single device, as well as for a wave power park of multiple wave energy converters. The power harvest can be increased in different ways, for example by optimizing the buoy, the generator or by implementing control on the operation of the device.This thesis focuses on studying wave energy converters in different wave climates by their power absorption. The main criteria influencing absorbed power are buoy size, weight on the system, damping force and available wave energy potential at the location of interest. The damping force can be computed by different approaches: constant optimal damping, resistive load (replicating passive control of currents in the stator windings) and RC-load (modeling a grid connected linear generator with an active rectification, such as phase angle compensation).Waves have a random nature. Therefore, the grid connection of the linear generator requires special solution. Power fluctuations of converted wave energy by the direct drive linear genera-tor may affect the integration into existing electrical grids. To study the connection of a single wave energy converter, as well as the wave park of three and ten devices, power hardware in the loop experiments have been carried out. The power quality analysis has been performed.Wave power has high potential and it can be integrated into the existing wind and solar energy production towards fully renewable microgrids. Yet, there is a chance of at least one quiet night during the year, when there are no wind and no waves. Estimation of frequency occurrence of absorbed power gives an insight into the regularity of such events. A case study in Hvide Sande, Denmark is presented. A mix of renewable energies (wind, solar and wave) is beneficial, as it gives a more stable energy supply with less variation in power production than when taken individually. Based on 30 years of historical data it is concluded, that the required battery size is sufficiently reduced for the renewable energy mix. The mix of wind, solar and wave has been shown to secure the lowest frequency of zero occurrences in power production and therefore is the most favorable choice for the future.
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| 4. |
- Rojas-Delgado, Brenda, et al.
(author)
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GA-Based Permutation Logic for Grid Integration of Offshore Multi-Source Renewable Parks
- 2022
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In: Machines. - : MDPI. - 2075-1702. ; 10:12
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Journal article (peer-reviewed)abstract
- This paper proposes and analyzes a genetic algorithm based permutation control logic applied to the aggregator of an offshore multi-source park. The energy losses at the common coupling point are accounted for in the feedback. This paper focuses on offshore distributed energy resources, such as floating photovoltaic (PV), wind, and wave power. The main contributions of this research are the development of a control system that is capable of tracking the set-point imposed by the demand curve for each source individually, the introduction of a capacity factor for combined offshore floating PV/wind/wave power farms, and the unveiling of pure offshore renewable sources as potential storage-less flexibility service providers. The results of a case study for a site near San Francisco showed that energy losses and capacity factors are positively influenced by implementing the proposed approach.
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| 5. |
- Ullah, Md Imran, et al.
(author)
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Analysis of a hybrid energy storage system in a grid-tied wave energy converter for varying power demand
- 2022
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In: 11th International Conference on Renewable Power Generation - Meeting net zero carbon (RPG 2022). - : Institution of Engineering and Technology. - 9781839537899 ; , s. 1-5
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Conference paper (peer-reviewed)abstract
- Wave energy is one of the emerging sustainable energy resources due to its high energy density and vast untapped areas. Nevertheless, the intermittency of wave resources is a significant challenge for the grid operator. Additionally, a varying grid demand is an added complexity to wave resources. Energy storage systems such as batteries and supercapacitors can be used to smoothen the power injection into the grid and match the available energy with the grid demand. Thus, this study compares battery energy storage with the hybrid energy storage system and proposes a control strategy to reduce the power fluctuations on the battery, allowing power delivery for varying grid demands. The study found that the hybrid system increases the system efficiency, in addition to the reduction in power fluctuations and enhancement of battery's performance, among other gains when the proposed control is implemented.
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