Wind2DC: Medium Voltage DC Power Take Off Technologies for Floating Offshore Wind Turbine Energy Conversion and Collection Systems

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The Wind2DC project will develop co-designed mechanical and electrical novel power take off systems for offshore wind-turbines that will these wind-turbines to be directly connected to a medium voltage dc (MVDC) collector system, as opposed to the ac collector systems that are current used. This will help exploit the full potential of offshore floating wind by: (1) reducing system costs, (2) Increasing the feasible size of offshore wind-farms, and (3) alleviate expected issues with dynamic cabling that will arise in floating wind-turbines. This supports the UK commitment to Net Zero by 2050 by enabling access to a large fraction of the estimated 4 TW of energy that is accessible from offshore wind. The project is strongly supported by industry, including Siemens Energy, Clas-SiC, JDR Cables, SSE Renewables.Floating Offshore Wind Turbine technology has the potential to unlock wind resources in offshore areas in which it is unfeasible to use conventional fixed-bottom turbine structures. This would provide a significant increase in exploitable offshore wind resources, with higher capacity factors than onshore or fixed-bottom offshore wind resources. The European floating wind resource has been estimated at 4 TW, a large share of which is located off Scotland and the south-west of England. To date, all offshore wind-farms have utilised ac electrical collection systems (in which the voltages and currents oscillate) to gather the power from each wind-turbine in the farm together before it is transmitted back onshore. In wind-farms close to shore, this transmission is also done using an ac system. in wind-farms that are far offshore the power is usually converted to dc (in which the voltages and currents are steady values) and transmitted back onshore through a High Voltage dc (HVDC) transmission line. Such systems require power-electronic converters to change the power from the wind-farm between ac and dc on both ends of the HVDC line. The advantage of dc systems is that the amount of conductors within the transmission cables is substantially reduced and, unlike ac transmission systems, there is no feasible limit on the length of the transmission system.Floating offshore wind-turbines devices require dynamic collection network cabling that can withstand the movement of the floating offshore wind-turbine platforms. In waters deeper than 100m it is difficult to fix the array cables to the seabed, leading to proposals in which the entire cable collection network is also floated. For such propositions a move to a Medium Voltage DC collection (MVDC) network, rather than a conventional ac collection network, would bring substantial benefits in reducing the weight of the cables themselves, as well as increasing their flexibility due to the reduction in conductor sizes need for a given power rating when moving from ac to dc. One of the main barriers to realising these MVDC collection networks is the unavailability of wind-turbine power-take off systems that are compatible with a high-power MVDC network voltages (expected to be in the region of 100 kilovolts plus).The Wind2DC project will focus on developing light-weight efficient power take off systems for Offshore Wind Turbines, providing a direct MVDC transmission compatible voltage output from each offshore wind-turbine, addressing the issue of cost-effective collection architectures, and enabling large scale offshore wind-turbines arrays with floating dynamic cabling. To do this the project will exploit novel generator, generator interface converter and dc-dc converter designs, with a focus on collaborative co-design of each of these aspects between the university teams that make up the project. To achieve this the researchers will exploit the potential next-generation wide bandgap semiconductors, which offer substantially increased voltage ratings as well as reduced switching losses, and novel modular electrical generator designs.