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Aquest ítem conté el treball original, així com una versió millorada del mateix a posteriori, Tot i que no hi ha cap projecte comercial d'energia eòlica flotant en funcionament, actualment el sector eòlic flotant està creixent significativament. La situació actual pel que fa la necessitat de reduir les emissions de carboni, l'alt potencial del recurs eòlic en aigües profundes, i les menors restriccions d'ús del sòl, impacte visual i soroll, fan de l’eòlica flotant una tecnologia molt atractiva. No obstant, encara es desconeix molt sobre els efectes sobre el medi ambient. En aquest treball es presenta el potencial d'escalfament global de l'eòlica marina flotant seguint la metodologia d'avaluació del cicle de vida, a més, es comenten diferents impactes ambientals descrits a la literatura. L'objectiu principal d'aquest treball és analitzar les emissions específiques de CO2 per a totes les zones viables a tot el món en funció de les condicions del lloc; distància a la costa, distància al port, profunditat de l'aigua, alçada significativa de les onades i potencial eòlic. Els resultats mostren moltes zones amb valors inferiors a 15 kgCO2eq/MWh, localitzades principalment a països del nord d'Europa, Amèrica del Sud, Egipte, Vietnam, Nova Zelanda, etc. i mostra una baixa intensitat de carboni en comparació amb altres tecnologies que són altament implementades en l’actualitat., Aunque no existe ningún proyecto comercial de energía eólica flotante en funcionamiento, actualmente el sector eólico flotante está creciendo significativamente. La situación actual en cuanto a la necesidad de reducir las emisiones de carbono, el alto potencial del recurso eólico en aguas profundas, y las menores restricciones de uso del suelo, impacto visual y ruido, hacen de la eólica flotante una tecnología muy atractiva. Sin embargo, aún se desconoce mucho sobre los efectos sobre el medio ambiente. En este trabajo se presenta el potencial de calentamiento global de la eólica marina flotante siguiendo la metodología de evaluación del ciclo de vida; además, se comentan diferentes impactos ambientales descritos en la literatura. El objetivo principal de este trabajo es analizar las emisiones específicas de CO2 para todas las zonas viables en todo el mundo en función de las condiciones del sitio; distancia a la costa, distancia al puerto, profundidad del agua, altura significativa de las olas y potencial eólico. Los resultados muestran muchas zonas con valores inferiores a 15 kgCO2eq/MWh, localizadas principalmente en países del norte de Europa, Sudamérica, Egipto, Vietnam, Nueva Zelanda, etc. y muestra una baja intensidad de carbono en comparación con otras tecnologías que son altamente implementadas en la actualidad., Although there are no floating wind energy commercial projects in operation, the offshore floating wind sector is now growing significantly. The current situation about the necessity to reduce the carbon emissions, the high potential of the wind resource in offshore deep waters, and the fewer restrictions regarding land use, visual impact and noise, make floating wind a very attractive technology. However, there is still much that is unknown about the effects on the environment. In this work, the global warming potential of floating offshore wind (FOW) is presented following the life cycle assessment (LCA) methodology, furthermore, different environmental impacts described in the literature are commented. The main aim of this work is to analyse the specific emissions of CO2 for all suitable areas worldwide depending on site conditions; distance to shore, distance to port, water depth, significant wave height and wind potential. Its results show a lot of zones with values below 15 kgCO2eq/MWh, located mainly in countries of north Europe, South America, Egypt, Vietnam, New Zealand, etc. and show a low carbon intensity compared with other technologies that are highly implemented in the actuality.

Floating offshore wind turbines (FOWT) have been extensively proven in model tests and are reaching currently a pre-commercial phase where large scale demonstrators are being built offshore. This transition increases the need for models able to assess the performance at suitable offshore locations. A simplified model is proposed that computes the dynamic response of FOWT to different met-ocean conditions and calculates the energy production considering the behavior of the structure as well as the downtime of the turbine due to exceeding operating limits. The model is validated against FAST and applied to three offshore sites. The motions response and hub acceleration are largest for West of Barra followed by Gulf of Maine and Costa Brava. The energy generation is also the highest at West of Barra, where a capacity factor of 75% is reached. A comparison between the energy generation of a bottom-fixed and FOWT indicates a difference of less than 1% for all sites. Finally, a sensitivity analysis of hub acceleration and platform pitch limits studies the impact on the capacity factor and downtime. The model can be useful for feasibility or pre-engineering studies and can be of interest for both investigators and developers of offshore wind projects., Peer Reviewed, Postprint (author's final draft)

This paper focuses on the droop-based dc voltage control design for multiterminal VSC-HVDC grid systems, considering the ac and the dc system dynamics. The droop control design relies on detailed linearized models of the complete multiterminal grid, including the different system dynamics, such as the dc grid, the ac grid, the ac connection filters, and the converter inner controllers. Based on the derived linear models, classical and modern control techniques are applied to design the different controllers, including a multivariable frequency analysis to design the grid voltage droop control. In combination with the droop control, a dc oscillation damping scheme is proposed in order to improve system performance. The control design is validated through simulations of a three-terminal system., Postprint (author's final draft)

To estimate the economic feasibility of floating and bottom-fixed substructures at various offshore sites, a generally applicable calculation tool has been developed. With this “LCOE calculation tool” it is possible to optimize the design and reduce the costs of deep offshore wind farms, by analyzing key aspects already during the planning and pre-design phase. Hereby the conducted breakdown of the several cost categories assists identifying main cost-drivers prior a final investment decision. Whereas the influence of varying site specific, technological and financial parameters on the cost-effectiveness is investigated in a sensitivity analysis. To validate and enlarge the tool’s dataset, the tool was applied to a real floating concept with the aim to compare the cost-effectiveness of floating solutions with their bottom-fixed counterparts., Peer Reviewed, Postprint (published version)

A new concept of a SPAR floating platform is being developed in the KIC-Innoenergy project AFOSP (Alternative Floating Platform Designs for Offshore Wind Turbines using Low Cost Materials). Members of the consortium are Gas Natural Fenosa, University of Stuttgart and Universitat Politècnica de Catalunya. The main differentiating aspects with respect to other SPAR prototypes are the monolithic nature of the whole structure, including both, the platform and the tower, the use of post-tensioned concrete as main material and the installation process. A comparison between similar steel and concrete designs demonstrates that the material cost for the concrete structure is around one third of the steel one. Considering that the concrete Oil & Gas platforms are virtually free of maintenance and have an extended lifetime, the real cost is less than 1/3 of the steel one, while the offshore tasks and the moorings systems have similar costs for both alternatives. Following a hydrostatic pre-design of the structure, coupled aero-servo-hydro-elastic analyses for a 5MW wind turbine have been performed by using an in-house FOWT model with a reduced number of degrees of freedom (DOF) and simplified aero- and hydrodynamics. With the obtained loads, the most relevant structural members have been checked, including a simplified fatigue limit state analysis, obtaining a lifetime over 50 years. Finally, a comprehensive cost analysis has been performed to obtain the Levelized Cost Of Energy (LCOE) for the developed platform., Postprint (published version)

The harmful effects of harmonics are an important issue in wind power plants (WPPs), especially in offshore applications. In offshore WPPs, the wind turbines are linked to the network through high-power converters that produce harmonics at relative low frequencies. Moreover, in the network of a WPP, the propagation of noncharacteristic harmonics and the effect of resonance contribute as well in boosting the harmonic distortion. In this paper, a solution for compensating the harmonics in a WPP by means of using hybrid filters is proposed. In this paper, not only the filtering solution is tested, but also a method for finding the best place where to connect the filter, based on a modal analysis or a harmonic modal resonance analysis, is implemented. The proposed solution has been tested by considering the model of a real 400-MW offshore WPP as the study case. As it will be shown, the hybrid filter is capable of damping the resonances in the plant, while the analysis conducted permits us to optimize its location in the plant, Postprint (published version)

This project presents the main features of each of the electricity transmission technologies available for offshore wind power and discusses their advantages and disadvantages in terms of technical, economic and environmental aspects. The transmission options studied are High Voltage Alternating Current (HVAC) and High Voltage Direct Current (HVDC). Within the HVDC there are two transmission technologies available, the classical Line Commutated Converter based HVDC and the most recently developed Voltage Source Converter based HVDC. As technical features, both operational and implementation issues are analyzed. Flexibility of control of active and reactive power or capacity to provide reactive power support are examples of the first, and size of offshore substation is an example of the latter. Cost-effectiveness and system losses are compared to derive a general rule for the best transmission option from the economic point of view and environmental concerns are also addressed. This enables reader to have a general overview of the factors that affect the decision of using one transmission technology or the other. The second part of the project is centered in the modeling and simulation of a particular case study using HVDC and HVAC. The studied system consists of a Full Scale Converter (FSC) based wind farm which is located 50 km off the shore. The wind farm has a rated power of 100MW which needs to be transmitted to the onshore grid either via VSC based HVDC or HVAC. Two models are built in order to learn about and implement the control systems of the converters. A detailed explanation on the control system design is included. Special attention is given to control strategies to comply with grid regulations related to fault ride-through capability and reactive power support. German Grid Codes are chosen as reference. In the case of HVDC reactive power support is performed by the grid-side VSC of the HVDC system, whereas in the case of HVAC it is performed by the grid, Outgoing

A new concept of a SPAR floating platform is being developed in the KIC-Innoenergy project AFOSP (Alternative Floating Platform Designs for Offshore Wind Turbines using Low Cost Materials). Members of the consortium are Gas Natural Fenosa, University of Stuttgart and Universitat Politècnica de Catalunya. The main differentiating aspects with respect to other SPAR prototypes are the monolithic nature of the whole structure, including both, the platform and the tower, the use of post-tensioned concrete as main material and the installation process. A comparison between similar steel and concrete designs demonstrates that the material cost for the concrete structure is around one third of the steel one. Considering that the concrete Oil & Gas platforms are virtually free of maintenance and have an extended lifetime, the real cost is less than 1/3 of the steel one, while the offshore tasks and the moorings systems have similar costs for both alternatives. Following a hydrostatic pre-design of the structure, coupled aero-servo-hydro-elastic analyses for a 5MW wind turbine have been performed by using an in-house FOWT model with a reduced number of degrees of freedom (DOF) and simplified aero- and hydrodynamics. With the obtained loads, the most relevant structural members have been checked, including a simplified fatigue limit state analysis, obtaining a lifetime over 50 years. Finally, a comprehensive cost analysis has been performed to obtain the Levelized Cost Of Energy (LCOE) for the developed platform., Postprint (published version)