Studies of the Grid Connection of Offshore Renewable Energy Sources : Technologies and Simulations

• A substantial increase in renewable energy sources connected to the electrical grid is imperative to achieve net-zero emissions from the electricity sector. Marine energy sources, like marine current power and wave power, have the potential to significantly contribute to the increase of electricity from renewable energy sources. A crucial aspect of enabling marine energy utilization is the development of electrical systems for offshore renewable energy. Hence, this thesis addresses challenges regarding the grid connection of offshore renewable energy.Two important questions for offshore renewable energy are how to construct the offshore electrical grid and how to transmit the power to the shore. This thesis provides a review of AC and DC collection grid topologies and compares HVAC and HVDC transmission for offshore applications. It is concluded that HVDC is the preferred technology for transmission distances exceeding 50 to 100 km.Regardless of the configuration of the offshore collection grid, the energy converters must be connected to the collection and distribution grid. Uppsala University has deployed a marine current energy converter in the river Dalälven in Söderfors, Sweden. The grid connection system at the test site is based on a back-to-back converter technology. In the thesis, a simulation model of the grid connection system of the energy converter is presented. The simulation model is used to evaluate MPPT methods for marine current power. An advanced hydrodynamic model based on a two-dimensional free vortex method is utilized for this purpose. Additionally, a low-complexity hydrodynamic model is incorporated into the simulation model to assess electrical grids for marine current energy. One AC and one DC collection grid, each comprising five marine current energy converters, are compared. Furthermore, three DC collection grids, each with ten marine current energy converters, are assessed and compared.The grid connection system at the Söderfors test site includes an LC filter connected to a power transformer. A novel transfer function is derived for this system, and the transfer function is verified with simulations and experimental investigations. It is shown that the derived transfer function accurately captures the frequency response of the experimental system.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering (hsv//eng)

Nyckelord

Grid connection

Filters

Power transformers

Offshore collection grids

HVDC transmission

HVAC transmission

Marine current energy

Maximum power point tracking

Engineering Science with specialization in Science of Electricity

Teknisk fysik med inriktning mot elektricitetslära

Publikations- och innehållstyp

vet (ämneskategori)

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