Centralized electricity generation in offshore wind farms using hydraulic networks

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Abstract

The work presented in this thesis explores a new way of generation, collection and transmission of wind energy inside a wind farm, in which the electrical conversion does not occur during any intermediate conversion step before the energy has reached the offshore central platform. A centralized approach for electricity generation is considered through the use of fluid power technology. In the proposed concept the conventional geared or direct-drive power drivetrain is replaced by a positive displacement pump. In this manner the rotor nacelle assemblies are dedicated to pressurize water into a hydraulic network. The high pressure water is then collected from the wind turbines of the farm and redirected into a central offshore platform where electricity is generated through a Pelton turbine. A numerical model is developed to describe the energy conversion process as well as the main dynamic behaviour of the proposed hydraulic wind power plant. The model is able to capture the relevant physics from the dynamic interaction between different turbines coupled to a common hydraulic network and controller. Two case studies are considered in the time-domain simulations for a hypothetical hydraulic wind farm subject to turbulent wind conditions. The performance and operational parameters of individual turbines are compared with those of a reference wind farm with conventional technology turbines, using the same wind farm layout and environmental conditions. For the presented case study, results indicate that the individual wind turbines are able to operate within the operational limits with the current pressure control concept. Despite the stochastic turbulent wind conditions and wake effects, the hydraulic wind farm is able to produce electricity with reasonable performance in both below and above rated conditions.