Control of a Hybrid OscillatingWater Column-Offshore Wind Turbine

Acceso restringido al texto completo pendiente de concesión de patenteThe 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

A control technique for hybrid floating offshore wind turbines using oscillating water columns for generated power fluctuation reduction

The inherent oscillating dynamics of floating offshore wind turbines (FOWTs) might result in undesirable oscillatory behavior in both the system states and the generated power outputs, leading to unwanted effects on critical, extreme, and fatigue loads, and finally to a premature failure of the facility. Therefore, this kind of system should be capable of lessening such undesired effects. In this article, four oscillating water columns (OWC) have been installed within a FOWT barge-type platform. A novel switching control technique has been developed in order to reduce oscillations of the system created by both wind and wave, as well as the fluctuations in the generated power, by adequately regulating the airflow control valves. While the impact of the coupled wind-wave loads has been considered, a set of representative case studies have been taken into account for a range of regular waves and wind speeds. The study relies on the use of response amplitude operators (RAO) that have been pre-processed and evaluated in order to apply the switching control technique. In this sense, the starting time of the switching for below-rated, rated, and above-rated wind speeds have been calculated using the platform’s corresponding pitch RAO. Additionally, the blades’ pitch and generator torque have also been regulated by means of a constant torque variable speed controller to capture maximum energy for below-rated wind speed conditions and to match the rated generator power for rated and above-rated wind speed conditions, respectively. In order to peruse the feasibility and performance of the proposed strategy, a comparison has been carried out between the uncontrolled traditional barge-type platform and the controlled OWCs-based barge FOWT. The results demonstrate that the proposed control approach can effectively and successfully decrease both the oscillations in the system’s modes and the fluctuations in the generated power.This work was supported in part by the projects PID2021-123543OB-C21 and PID2021-123543OB-C22 (MCIN/AEI/10.13039/501100011033), Basque Government Groups IT1555-22 and Margarita Salas MARSA22/09 (UPV-EHU/MIU/Next Generation, EU)

Performance Analysis on the Use of Oscillating Water Column in Barge-Based Floating Offshore Wind Turbines

Undesired motions in Floating Offshore Wind Turbines (FOWT) lead to reduction of system efficiency, the system’s lifespan, wind and wave energy mitigation and increment of stress on the system and maintenance costs. In this article, a new barge platform structure for a FOWT has been proposed with the objective of reducing these undesired platform motions. The newly proposed barge structure aims to reduce the tower displacements and platform’s oscillations, particularly in rotational movements. This is achieved by installing Oscillating Water Columns (OWC) within the barge to oppose the oscillatory motion of the waves. Response Amplitude Operator (RAO) is used to predict the motions of the system exposed to different wave frequencies. From the RAOs analysis, the system’s performance has been evaluated for representative regular wave periods. Simulations using numerical tools show the positive impact of the added OWCs on the system’s stability. The results prove that the proposed platform presents better performance by decreasing the oscillations for the given range of wave frequencies, compared to the traditional barge platform.This work was supported in part by the Basque Government, through project IT1207-19 and by the MCIU/MINECO through the projects RTI2018-094902-B-C21 and RTI2018-094902-B-C22 (MCIU/AEI/FEDER, UE)

A regressive machine-learning approach to the non-linear complex FAST model for hybrid floating offshore wind turbines with integrated oscillating water columns

Offshore wind energy is getting increasing attention as a clean alternative to the currently scarce fossil fuels mainly used in Europe's electricity supply. The further development and implementation of this kind of technology will help fighting global warming, allowing a more sustainable and decarbonized power generation. In this sense, the integration of Floating Offshore Wind Turbines (FOWTs) with Oscillating Water Columns (OWCs) devices arise as a promising solution for hybrid renewable energy production. In these systems, OWC modules are employed not only for wave energy generation but also for FOWTs stabilization and cost-efficiency. Nevertheless, analyzing and understanding the aero-hydro-servo-elastic floating structure control performance composes an intricate and challenging task. Even more, given the dynamical complexity increase that involves the incorporation of OWCs within the FOWT platform. In this regard, although some time and frequency domain models have been developed, they are complex, computationally inefficient and not suitable for neither real-time nor feedback control. In this context, this work presents a novel control-oriented regressive model for hybrid FOWT-OWCs platforms. The main objective is to take advantage of the predictive and forecasting capabilities of the deep-layered artificial neural networks (ANNs), jointly with their computational simplicity, to develop a feasible control-oriented and lightweight model compared to the aforementioned complex dynamical models. In order to achieve this objective, a deep-layered ANN model has been designed and trained to match the hybrid platform's structural performance. Then, the obtained scheme has been benchmarked against standard Multisurf-Wamit-FAST 5MW FOWT output data for different challenging scenarios in order to validate the model. The results demonstrate the adequate performance and accuracy of the proposed ANN control-oriented model, providing a great alternative for complex non-linear models traditionally used and allowing the implementation of advanced control schemes in a computationally convenient, straightforward, and easy way.This work was supported in part by the Basque Government through project IT1555-22 and through the projects PID2021-123543OB-C21 and PID2021-123543OB-C22 (MCIN/AEI/10.13039/501100011033/FEDER, UE). The authors would also like to thank the UPV/EHU for the financial support through the María Zambrano grant MAZAM22/15 and Margarita Salas grant MARSA22/09 (UPV-EHU/MIU/Next Generation, EU) and through grant PIF20/299 (UPV/EHU)

Fuzzy logic control of an artificial neural network-based floating offshore wind turbine model integrated with four oscillating water columns

Renewable energy induced by wind and wave sources is playing an indispensable role in electricity production. The innovative hybrid renewable offshore platform concept, which combines Floating Offshore Wind Turbines (FOWTs) with Oscillating Water Columns (OWCs), has proven to be a promising solution to harvest clean energy. The hybrid platform can increase the total energy absorption, reduce the unwanted dynamic response of the platform, mitigate the load in critical situations, and improve the system's cost efficiency. However, the nonlinear dynamical behavior of the hybrid offshore wind system presents an opportunity for stabilization via challenging control applications. Wind and wave loads lead to stress on the FOWT tower structure, increasing the risk of damage and failure, and raising maintenance costs while lowering its performance and lifespan. Moreover, the dynamics of the tower and the platform are extremely sensitive to wind speed and wave elevation, which causes substantial destabilization in extreme conditions, particularly to the tower top displacement and the platform pitch angle. Therefore, this article focuses on two main novel targets: (i) regressive modeling of the hybrid aero-hydro-servo-elastic-mooring coupled numerical system and (ii) an ad-hoc fuzzy-based control implementation for the stabilization of the platform. In order to analyze the performance of the hybrid FOWT-OWCs, this article first employs computational Machine Learning (ML) techniques, i.e., Artificial Neural Networks (ANNs), to match the behavior of the detailed FOWT-OWCs numerical model. Then, a Fuzzy Logic Control (FLC) is developed and applied to establish a structural controller mitigating the undesired structural vibrations. Both modeling and control schemes are successfully implemented, showing a superior performance compared to the FOWT system without OWCs. Experimental results demonstrate that the proposed ANN-based modeling is a promising alternative to other intricate nonlinear NREL 5 MW FOWT dynamical models. Meanwhile, the proposed FLC improves the platform's dynamic behavior, increasing its stability under a wide range of wind and wave conditions.This work was supported in part by the Basque Government through project IT1555-22 and through the projects RTI2018-094902-B-C22 (MCIU/AEI/FEDER, UE), PID2021-123543OB-C21 and C22 funded by MCIN/AEI/10.13039/501100011033. The authors would also like to thank the UPV/EHU for the financial support through the Maria Zambrano grant MAZAM22/15 funded by the European Union-Next Generation EU and through grant PIF20/299

Switching Control Strategy for Oscillating Water Columns Based on Response Amplitude Operators for Floating Offshore Wind Turbines Stabilization

In this article, a new strategy for switching control has been proposed with the aim of reducing oscillations in floating offshore wind turbines. Such oscillations lead to a shortage in the system’s efficiency, lifespan and harvesting capability of wind and wave energies. In order to study the decreasing of undesired oscillations in the system, particularly in pitch and top tower fore-aft movements, a square-shaped platform barge equipped with four symmetric oscillating water columns has been considered. The oscillating water columns’ air flux valves allow to operate the air columns so that to control the barge movements caused by oscillatory motion of the waves. In order to design the control scheme, response amplitude operators have been used to evaluate the performance of the system for a range of wave frequency profiles. These response amplitude operators analysis makes it possible to implement a switching control strategy to adequately regulate the valves opening/closing transition. The obtained results show that the proposed controlled oscillating water column-based barge present a better performance compared to the traditional barge one. In the case study with the period of 10 s, the results indicate the significant oscillation reduction for the controlled oscillating water column-based system compared to the standard barge system by 30.8% in pitch angle and 25% in fore-aft displacement.This work was supported in part by the Basque Government, through project IT1207-19 and by the MCIU/MINECO through the projects RTI2018-094902-B-C21 and RTI2018-094902-B-C22 (MCIU/AEI/FEDER, UE)

Complementary Airflow Control of Oscillating Water Columns for Floating Offshore Wind Turbine Stabilization

The implementation and integration of new methods and control techniques to floating offshore wind turbines (FOWTs) have the potential to significantly improve its structural response. This paper discusses the idea of integrating oscillating water columns (OWCs) into the barge platform of the FOWT to transform it into a multi-purpose platform for harnessing both wind and wave energies. Moreover, the OWCs will be operated in order to help stabilize the FOWT platform by means of an airflow control strategy used to reduce the platform pitch and tower top fore-aft displacement. This objective is achieved by a proposed complementary airflow control strategy to control the valves within the OWCs. The comparative study between a standard FOWT and the proposed OWC-based FOWT shows an improvement in the platform’s stability.This work was supported in part by the Basque Government, through project IT1207-19 and by the MCIU/MINECO through the projects RTI2018-094902-B-C21 and RTI2018-094902-B-C22 (MCIU/AEI/FEDER, UE)

A Novel Control Strategy for Oscillation Reduction in Floating Wind Turbines

[Resumen] En este trabajo se ha propuesto una nueva estrategia de control para mejorar la estabilidad de turbinas eólicas flotantes (FWT). Al objeto de estudiar la reducción de oscilaciones no deseadas en el sistema, y en particular en los movimientos de cabeceo de la plataforma y de proa-popa de la nacelle, se ha considerado una plataforma tipo barcaza de forma cuadrada y equipada con cuatro columnas de agua oscilantes (OWC) colocadas de manera simétrica. De esta forma, las válvulas de control de flujo de aire de las cámaras de captura permiten operar las citadas columnas de aire para controlar los movimientos de la barcaza causados por la dinámica oscilatoria de la ola incidente. Para ello, se ha efectuado un análisis de los operadores de amplitud de respuesta (RAO) que permite implementar una nueva estrategia de control de conmutación para regular adecuadamente la transición apertura/cierre de las válvulas de control de flujo. Los resultados obtenidos muestran que la topología de plataforma híbrida propuesta, dotada de sistemas controlados OWC, presenta un mejor rendimiento que una plataforma análoga tradicional.[Abstract] In this work, a new control strategy has been proposed to improve the stability of floating wind turbines (FWT). In order to study the reduction of undesired oscillations in the system, and in particular in the platform pitch and fore-aft nacelle movements. A square-shaped barge-type platform has been considered and equipped with four symmetrically located Oscillating Water Columns (OWCs). In this way, the air flow control valves of the capture chambers allow the aforementioned air columns to be operated so that to control the movements of the barge caused by the oscillatory dynamics of the incident wave. To do so, an analysis of the response amplitude operators (RAO) has been carried out, which in turn allows the implementation of a new switching control strategy to properly regulate the transition of the flow control valves. The results obtained show that the proposed hybrid platform topology, equipped with OWC controlled systems, presents better performance than a traditional analog platform.Gobierno Vasco; IT1207-19Los autores del presente trabajo quisieran agradecer el apoyo del Gobierno Vasco mediante el proyecto IT1207-19 y del MCIU/MINECO a través de los proyectos RTI2018-094902-B-C21 y RTI2018-094902-B-C22 (MCIU/AEI/FEDER, UE)https://doi.org/10.17979/spudc.978849749804

Dual Airflow Control Strategy for Floating Offshore Wind Turbine Stabilization Using Oscillating Water Columns

The stability of Floating Offshore Wind Turbine (FOWT) has been the focus of many researchers in the last years. Many concepts proposed the use of passive structural control such as inerter and Tuned Mass Dampers (TMD). This paper presents a new concept combining a barge-based FOWT with Oscillating Water Columns (OWC) to help reduce the undesired vibrations induced from waves and wind. In this work, an airflow control strategy developed for the OWCs integrated in the barge platform of a FOWT. The control strategy has been designed to lessen the pitching of the platform and the displacements of tower fore-aft with the intention of stabilizing the floating platform. This objective is achieved by controlling the air valves located at the top of the OWCs’ capture chambers. The comparative study between the FOWT with standard barge and the proposed FOWT with OWC-based barge, based on the analysis of the free decay responses, displays an enhancement in the stability of the platform.This work was supported in part by the Basque Government through project IT555-22 and by the MCIU/MINECO through the projects RTI2018-094902-B-C21 and RTI2018-094902-B-C22 (MCIU/AEI/FEDER, UE)

A Machine-Learning Approach for the Development of a FOWT Model Integrated with Four OWCs

The wind-wave excitations cause structural vibrations on the Floating Offshore Wind Turbines (FOWT) pressing the power generation efficiency and reducing the life expectancy. In particular, tower-top displacement and barge-type platform pitch dynamics are extremely sensitive to wind speed and wave elevation to the point that may even lead to structural instability in extreme conditions. Having into account that computational techniques such as Artificial Neural Networks (ANNs) are widely used in artificial intelligence because of their strong predicting and forecasting capabilities, the aim of this article is to create a deep-layer ANN model that incorporates Oscillating Water Columns (OWCs) into the barge platform. This ANN model enables to address stability issues of the hybrid floating offshore wind platform. The proposed control-oriented model has been successfully validated to achieve adequate dynamic behavior and structural performance using FAST.Basque Government IT555-22, PID2021-123543OB-C21 and PID2021-123543OB-C22 (MCIN/AEI/10.13039/501100011033/FEDER, UE