On the Control of a Seawater-Hydraulic Wind Farm with the Delft Offshore Turbine

Abstract

Offshore wind energy is a promising prospect to meet the ever-growing demand for energy. Its reputation is, however, sullied by high costs not yet competitive with conventional energy resources. The Delft Offshore Turbine (DOT) attempts to radically reduce the Levelized Cost of Energy (LCOE) of offshore wind by utilising a seawater-hydrostatic transmission from individual wind turbines to a central power station, where power is generated collectively. Recent theoretical research on the DOT employed variable displacement pumps in the wind turbines interconnected through a collective pipeline. A variable displacement pump does not yet commercially exist and leaves the implementation of a fixed-displacement pump more viable in the near future. Recent practical research implemented a fixed-displacement pump with an individual pipeline. To benefit from the economy of scale however, a collective pipeline is preferred. The DOT wind farm considered in this thesis incorporates fixed-displacement pumps interconnected through a collective pipeline. The difficulty herein arises from the combination of an equal hydraulic torque but varying aerodynamic torque throughout the wind farm. The combined effect results in the inability to control individual rotor speeds, which inevitably leads to suboptimal individual rotor efficiency. This research explores a novel control strategy that obtains the best suboptimal performance when the wind turbines are controlled through a collective pressure.