Control of a Hybrid Oscillating Water Column-Offshore Wind Turbine

Abstract

The wind energy sector is spreading its wings all over the world, and wind power is gradually displacingfossil fuels. Due to the impacts of climate change and global warming, renewable energy resources suchas wind and wave power are gaining popularity. It is essential to construct wind and wave supplyinfrastructure in order to tackle these challenges. Floating Offshore Wind Turbines (FOWT) have playeda game-changing role in gathering more clean, renewable wind and wave resources and producing morepower.Offshore energy machines offer greater potential than onshore machines due to larger capacity factors,more accessible area, and less visible effects. Oscillating water columns may be incorporated into theFOWTs' platform for harnessing both wind and wave power supply. The integrated system of FOWTOWCshas the potential to significantly reduce system costs by leveraging shared operation andmaintenance and common grid infrastructure. It can also improve the system's smoothed power outputand efficiency. However, one of the difficulties that lies ahead is the stability of FOWTs in order toreduce unwanted platform vibrations and capture as much energy as feasible. These undesirablemovements diminish aerodynamic efficiency, limit tower fatigue life, and raise loads on blades, rotorshaft, yaw bearing, and tower base. As a result, it is vital to keep the FOWT's platform movements withina reasonable range.In this thesis, four oscillating water columns (OWC) have been integrated into the FOWT's bargeplatform to decrease the system's oscillations. To analyse the behavior of the hybrid system, responseamplitude operators (RAO) have been evaluated. Using RAOs, a switching control method have beenintroduced to manage the transition between closing and opening OWCs' valves. The controller reducesthe oscillations in a barge-based FOWT supporting 5 MW wind turbine. The considered environmentalconditions consist of various sea states with low-rated, rated and above-rated wind speeds.The results show that the considered switching control strategy has been able to reduce the oscillations inthe barge-based FOWT efficiently. Consequently, this oscillation reduction lead to decease thefluctuations in the generated power output. Also, the results illustrate that the average power outputincreases in low-rated wind speeds.These results have been obtained using the MultiSurf, WAMIT, FAST, and MATLAB-Simulink tools.Finally, to assess the performance of the suggested technique, a comparison has been made between thecontrolled OWCs-based barge and the traditional barge-based platform.This thesis work is structured as follows: the first chapter provides an overview of FOWT types and waveenergy converters. It also discusses the advantages and disadvantages of the hybrid FOWT-oscillatingwater columns. The second chapter summarizes the current state of the art in FOWT stabilizing methods.The problem statement and thesis goals are then explained. Chapter 3 describes the performance ofOWCs in barge-based FOWTs for various sea conditions. In chapter 4, a switching control method ispresented to reduce oscillations in the hybrid FOWT-OWCs system when wind power is absent. Chapter5 develops a switching control approach to decrease system oscillations in diverse sea conditions andwind speed scenarios. In addition, the performance of the controlled OWCs-based barge platformplatform in terms of generated power has been examined in this chapter. Finally, in chapter 6, thefindings of the thesis and future works are summarized.