Project

Floating offshore wind turbines (FOWT) is a new technology, which is still in its developing stage. FOWT could be the solution in order to increase the possible construction areas, as they are more suitable for deeper waters. But the downside is that a floating foundation introduces additional dynamics to the system, which could lead to complex constructions and thereby decrease their cost/effectiveness. If the FOWT control systems take these dynamics into account it could minimize the impact of these and thereby increase the advancement

of FOWTs. Therefore in this project it is sought to develop a physically scaled model of a real wind turbine, which is able to be controlled similar to real wind turbine systems, this includes generator torque control and blade pitching control. The physical model must be constructed in order to test and verify these controlling methods. In this project the scaled nacelle of a wind turbine is designed and constructed, together with the power electronics. It is a 1:35 scaled model of the NREL 5 MW reference wind turbine. Furthermore, blades are designed and constructed in order to match the scaled thrust force of the reference wind turbine. The dynamic models of the subsystems of the wind turbine are developed and controllers for them are designed. The controller's impact is simulated in simulink models of the subsystems.

This project enables Danish participation in IEA Wind Task 44: Farm Flow Control. The focus is on control strategies to mitigate wake effects in wind farms. The purpose of IEA Wind Task 44 is to coordinate international research in the field of wind field control inside wind farms. The technology used for this task covers a wide range, but focuses primarily on control algorithms and strategies and how they are transferred to real-world operational improvements.

The intention is to bring together ongoing research results as well as best industry practice, create an overview of control strategies and algorithms and investigate how uncertainties affect the performance and potential for implementation of wind farm control.
The result is guidance for the wind industry and researchers on the current control algorithms, requirements, barriers to adoption, future directions and expected benefits of wind farm control.

This project aims to suppress the oscillation motion of floating offshore wind turbines and to improve the structural safety margin of the turbines. The tension leg platform has good vertical stiffness, but insufficient horizontal stiffness and are prone to yawing motion. By establishing a vibration isolation system to resist and dissipate wave impact and wind load impact. The excitation and damage caused by external loads to the wind turbine can be effectively mitigated. The response of the wind turbine is analyzed based on the wave load spectrum and the response curve of the floating platform is calculated using numerical simulation as a basis for designing the hybrid vibration isolation system. A suitable control strategy is selected to first dissipate the waves by controlling the actuators and then dissipate the energy using hybrid vibration isolation. Simulations and experimental studies are used to select the appropriate dynamic parameters for the vibration isolation system to achieve the desired response of the wind turbine. The life state analysis of key components such as tension legs is carried out. The performance degradation characteristics and laws of wind turbines under low-frequency cyclic waves are studied to ensure their safe operation.

This project includes modelling, designing and testing of a 150 kW solid-oxide electrolysis (SOE) system for renewable hydrogen production. The produced hydrogen can be used as a component for future green electro-fuels like ammonia or methanol.

The SOC stacks will be operated by the novel AC:DC control method which enables dynamic hydrogen production due to fluctuating electricity production from wind turbines.

The AC:DC method requires bi-directional power flow of the stacks and dedicated power electronic converters will therefore be developed in this project as well.

When the project is successfully completed, the consortium will have demonstrated manufacturing and operation of a power-to-X plant with AC:DC operation technology. This is an important milestone on the path for megawatt production.

The pitch system of a wind turbine is one of the systems used for regulating the power production of the wind turbine. The Pitch system may turn the blades of the turbine from approximately 0 to 90 degrees around its own axis and thus regulate the energy input from the wind to the turbine. If the blades are turned into a 90 degree position the turbine will stop rotating and the energy production is stopped. If an error occurs in the turbine and it is necessary to shut the turbine down before extensive damage occurs, an emergency stop is performed by turning the blades to their 90 degree position. The pitch system is the primary safety system of the turbine.

As the pitch system has an essential function of the wind turbine it is extremely important that the system is reliable and available. Especially for offshore wind turbines it is extremely important that no other maintenance than the scheduled has to be performed. Research shows that pitch systems are currently responsible for 22% of wind turbines' total downtime.
A combination of lower cost and increased reliability and availability on the hydraulic pitch system will reduce both the total cost of ownership (TCO) and Total Cost of Energy (TCE).

This project aims to significantly increase the reliability and availability of the pitch systems compared to current hydraulic and electric pitch systems. This is done through a modular way of thinking in which the entire system is brought out in the rotating hub and distributed in three individual systems - one for each wing. Through this transformation it is the goal to reduce the price by 20% while the number of components is lowered by 10%.

To increase uptime for a hydraulic pitch system, external leakage from the hydraulic components must be eliminated. This will be achieved through reductions in external leakage paths to both the environment in the hub of the turbine and nature where the turbine is erected. In 2012, 74% of the offshore wind turbines were installed with hydraulic pitch systems. Of the total offshore capacity, 86% of the turbines are controlled by hydraulic pitch systems (2012). It is the goal for the new hydraulic pitch system that it must be in new offshore wind turbines already being installed with hydraulic pitch, but by the modular thinking and plug and play setup it is possible to access turbine manufacturers who use electric pitch and thus take greater market share.

The purpose of the project is to mature the idea of ​​a novel approach for establishing reliable digital twins of offshore wind turbines, which can be employed for improved operation and maintenance of these systems. Upon successful completion of this, the intention is to apply for an Innovation Fund project or EUDP project. The aim is to develop digital twins based on closed-loop model updating and incorporate them in a systematic procedure for structural health monitoring of wind turbines, and (2) aim To develop data-driven control strategies for vibration damping.

The goal of the project is to significantly strengthen the scientific basis for the wind power industry in general and specifically the Danish wind power industry’s position in offshore applications.

To meet the goal the proposed research must have a significant potential for reduction of cost of energy from large offshore wind farms, and for contributing to reduction of the economic risks arising from inadequately founded design.

The key design driver for most offshore structures is safety. For offshore wind turbines/farms, however, the main design driver is economy and therefore there is a strong requirement for enhancing design tools and avoiding conservatism. Consequently, focus is on the following issues:

1. Mutual shadow effect between large blocks of wind turbines – ignorance of the effect may have disastrous consequences for the economy.
2. Extreme structural loading of offshore wind turbines – detailed understanding and description of extreme winds and gusts and resulting loads is crucial for the safety and economics of the wind turbines.
3. Interaction of large wind farms with waves and current – understanding and modeling may lead to reduced design loads on wind turbine units placed in the downwind end of the wind farms.
4. Grid connection and reliability – An unreliable grid caused by high wind energy penetration is an obvious barrier for the dissemination of the technology.
5. Optimized operation and maintenance for offshore wind farms – presently more than a third of the cost of energy from offshore wind farms relates to O&M and the potential for reductions is therefore large.

The project is sponsored by The strategic Research council and have participant from Risø National Laboratory, Elsam Engineering, Insitut for Mekanik, Energi og Konstruktion DTU, DHI, Svend Ole Hansen and Institute of Energy Technology AAU.

The institute of Energy Technology is especially involved in issue 4 in this project, by Birgitte Bak-Jensen, and also a Ph.D project is set up together with Risø and Elsam Engineering, with the title: Offshore Wind Power – Grid Connection and Reliability, see this project.

This Ph.D. project is carried out at Dong Energy in cooperation with Risø National Laboratory and Aalborg University.

The aim of the PhD project is to investigate the influence of wind generation on the reliability of power systems. This task is particularly important for large offshore wind installations, because failure of a large wind farm will have significant influence on the balance in the power system, and because offshore sites are normally more difficult to access than onshore installations. The reliability of power production from a wind farm depends on wind speed conditions, the wind turbines themselves, the system layout and the grid connection; besides, the offshore environment poses new challenges to face for the installers.

The project has been divided into three parts. Firstly, a model for yearly generation assessment of offshore wind farms has been developed: this model includes wind speed randomness and variability, components (e.g. wind turbines, internal cables and connectors to shore) failures, influence of site environment and some minor aspects of relevance. Secondly, this model has been used for evaluating the so-called HLI analysis (Hierarchical Level I), where the system adequacy to supply the load is assessed. The power system under study includes conventional power plants, an aggregated load and distributed generation together with offshore wind generation, whereas transmission facilities are neglected in this type of simulation. These two assessments are performed considering a sequential Monte Carlo simulation: this approach has shown more flexibility and completeness in the analysis of wind generation than analytical techniques.

With these two models, that are currently available, some sensitivity analyses will be carried out in the next months. Besides, some of the models will be used for performing an HLII analysis: in this type of study, the transmission facilities are included in the power system model and the adequacy of the system generation is evaluated including the availability of transmission lines and cables.

All analyses in the project are carried out by the use of the software Matlab and the power system analysis tool Power Factory from DigSILENT: simulations will include steady-state conditions as well as dedicated reliability analyses.