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Platform control for energy and loads on a novel ultra-flexible floating offshore wind turbine substructure
Grant, Elenya Sophia
Grant, Elenya Sophia
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2022
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Abstract
The cost of floating offshore wind turbines must be reduced to be competitive with non-renewable energy sources. The Ultra-flexible Smart FLoating Offshore Wind Turbine (USFLOWT) project aims to reduce the cost of wind energy by using the unique semi-submersible substructure design called the SpiderFLOAT. Unlike conventional floating substructure designs, the SpiderFLOAT has built-in platform control options and is light-weight and ultra-flexible. Preliminary baseline turbine controller testing motivated the design objective of increasing energy capture in near-rated wind speeds. For a singular near-rated wind speed case study, we investigate how the turbine blade pitch signal may be best tuned in parallel with varying can ballast levels and distributions to optimize power generation, rotor speed regulation, and stabilize platform oscillations. In this thesis, we propose an open-loop low-bandwidth buoyancy-can ballast controller to partially compensate the shaft tilt angle and mean platform pitch angle for increased power generation and reduced tower-base fatigue loading compared to the baseline controller. The buoyancy-can ballasting controller is shown to perform well across three metrics: it does not interfere with the operational turbine controller, maintains the platform pitch angle within an allowable range, and does not require design modifications necessary to avoid component fatigue failure due to the additional ballast mass. We evaluate the robustness of the controller to varying wind misalignment to inform future controller optimization. Finally, we discuss routes for future optimization or consideration of the buoyancy-can ballast controller.
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