Energy Transfer for Offshore Wind Energy

Project Description:

Offshore wind energy has been demonstrated as a viable technology for the decarbonisation of UK power, however there are significant challenges in the transmission of this energy to shore [1]. One of the significant challenges of floating wind power is the dynamic cabling, where mechanical stresses on the electrical connection can result in fatigue and early dielectric failure. Currently, issues in the electical cabling results in 47% of failures and this is expected to increase as larger wind turbines are installed further apart, further from shore and in deeper water, all of which increase the forces applied to the cable [2]. The project is to investigate three potential technology solutions for the realisation of a collection network between off-shore wind turbines and a centralised collection point that will enable a reduction in the installation cost of an offshore wind farm. This will facilitate the creation of larger scale wind farms offshore, enabling the deployment of higher power generators.

The research hypotheses to be investigated are

1. Understanding the move to higher voltages in the interconnect, including the move to MVDC or low frequency AC [3,4]. This has the potential to reduce the mass of copper required in the cable, offering increased flexibility of the interconnecting cable and the possibility of floating cables.

2. Understanding the potential use of superconducting cables in electrical systems, where the switching frequency of power electronic converters is present. The AC losses from the ripple currents in the DC power at kHz is not known, The move to superconducting cables supports the move to higher voltages and lower frequencies, giving greater flexibility in system design.

3. Wireless power transfer has been demonstrated over short and medium range applications, such as car charging. Whilst the current demonstrations do not presently meet the efficiency of a hardwired system, the significant reduction in installation costs and the removal of a significant failure mechanism. This is the first consideration of wireless power transfer at the proposed power levels and distances, offering an opportunity for a significant research contribution.

The proposed PhD project will consider the potential solutions to the hypotheses above and compare these to the existing flexible AC cable solution that is used for offshore wind farms.

Small scale laboratory demonstrators will be used to validate the mathematical modelling of the different potential solutions in the second year, using the experimental facilities available in the Department of Engineering. The validated models will the be used to identify the optimium power transfer system for use in off shore wind networks, in terms of the efficiency, capital expenditure and reliability, which will be inferred from mathematical foundations and physics of failure data from the literature [5].

The later stages of the project will be to implement the optimum solution in a laboratory based multi-kW power transfer system. This stage of the project has the potential to link to other Aura funded PhDs at Durham, including the MVDC wave energy integration project and to use simulated wind turbine facilities. This will ensure that the power provided to the transfer system is representative of a real system, including voltage transients caused by switching of devices, ensuring relevance of the data to the wind community.

The testing has the potential to include support from the Hardware In Loop capabuility in the University, that can mimic the behaviour of the collection network and wider distribution grid.

Methodology

The initial stage of the project is to undertake a literature study of the different power transfer techniques. The findings from the literature review will be supplemented with computer modelling to determine the operating conditions and performance of the different technology solutions. These models will also enable the identification of suitable design parameters to enable the constriction of laboratory scale demonstartors. The final stage of the project focusses on the experimental validation of the modelling opf the optimum system, before the demonstration of an industrially relevant (kW class) demonstrator system. This demonstrator will be used to provide parameters to support a predictive model for the utilisation of the proposed solution in the realisation of a power transfer system for off shore wind farms, including considerations of the installation cost and the effect on the unit price.

References & Further Reading

[1] Firestone, et al, Environmental Innovation and Societal Transitions, Vol. 29 (2018) pp. 90

[2] Offshore Wind subsea Power Cables, El Mountassir, Strang-Moran, ORE Catapult

[3] Chaithanya, et al, International Journal of Renewable Energy Sources, Vol. 8 (2018) pp. 141

[4] Apostolaki-Iosifidou, et al, IEEE Power and Energy Technology Systems Journal, DOI 10.1109/JPETS.2019.2898688

[5] Offshore Wind Cable Manufacturing and Installation Forecast 2018-2028