ABSTRACT

The blade pitch controller with input saturation can suppresses negative damping, but this function reduces the power generation performance. In this study, a time-domain analysis was conducted by parametrically changing the floating body geometry and control settings to investigate whether the performance degradation caused by the control can be suppressed by increasing the restoring force of the floating body. The results of the study did not indicate that the restoring force of the floating structure had a significant effect on the control, but we determined that the method of changing the shape of the floating structure had a significant effect on the tower base load.

INTRODUCTION

As a candidate for the main power source in a carbon-neutral society, wind power generation is growing at an accelerating pace. The global installed capacity of wind power reached 837 GW in 2021 (GWEC, 2022), more than three times that of 10 years ago. Wind power generation facilities are actively being deployed offshore in order to further increase the installed capacity, and offshore wind farms have begun operating in several areas of the ocean including the North Sea. Until now, foundation structures for offshore wind power generation have been dominated by support structures such as jacket type and monopile foundations that take advantage of shallow coastal waters. However, floating offshore wind turbines (FOWTs), which can be installed regardless of water depth, are gaining more interest as an alternative.

The floating offshore wind farm: Hywind Tampen is scheduled to be operation from 2023(Equinor, 2022) after multiple demonstration projects and research and development. Because the entire facility of a FOWT is subject to turbulence caused by external forces such as waves, it is important to clarify the impact of the FOWT's motion on the generator and the integrity of the entire floating support structure, including mooring cables. A coupled analysis should be conducted for the floating structure as well as the elastic response of the blades and tower. Elastic analysis software such as FAST, developed by NREL, and Bladed, developed by DNVGL, are typically used for this analysis. It is also important to use the software to evaluate the effect of the blade pitch control of the wind turbine in the analysis. The blade pitch control of a wind turbine is performed with the goal of maximizing the amount of electricity generated, but when the support structure is a floating structure, it has been shown that fluctuations in the thrust load generated by rotor speed changes may increase the floating body motion. This phenomenon of increased floater motion is called negative damping (Larsen, 2007, Chujo, 2012). In the control setup of FOWTs, it is important to select a control method that can provide an optimal solution for power generation while also taking the safety of the support structure into consideration. In addition to the safety of the floating support structure, cost is also a concern. The larger the structure, the more likely it is to be able to reduce the amount of motion in waves, but at the same time, the weight of the material increases, which increases the manufacturing cost. The floating structure should be designed with consideration of the restoration performance and other factors.

This content is only available via PDF.
You can access this article if you purchase or spend a download.