Project

To transfer energy from collected offshore wind farms over a long distance, HVDC transmission is preferred over HVAC in terms of efficiency and economy. Several multi-stage configurations have been proposed in the literature. However, the multi-stage configuration generally results in a large size due to a large number of conversion stages, relatively high cost, and low efficiency and power density. Also, the independent control of several converters and communication among the sources make the system complex. To overcome these disadvantages, multi-port modular DC/DC topologies have been suggested. Multiport converters are highly non-linear MIMO systems with many control variables. Also, the coupling between the control variables makes modeling and control system design complicated. Despite such complexity, advanced control techniques have not been comprehensively studied. Moreover, most controller design work on multiport converters has not considered the uncertainties of the converter model. In this Ph.D. study, a robust controller is implemented for multi-port modular DC/DC converter for offshore wind farms application.

Turkey is one of the fastest-growing energy markets in the world, with an annual 8% increase in energy demand. By the end of 2018, the total installed capacity and electricity production of Turkey was 88.5 GW and 300.7 TWh, respectively. Nowadays, more than 70% of all electricity production is supplied by fossil resources, and almost 30% of all electricity production comes from renewables, mainly hydro, while wind constitutes only 6.6% of the total electricity mix.

The wind and solar energy rate in total consumption are planned to be increased by at least 30% in the coming five years according to the 2023 vision plan of Turkey. However, due to the intermittent nature of wind energy, large-scale wind power integration may pose some serious challenges to Turkey's power system. Therefore, planning analysis and designing efforts are required to ensure the smooth, secure and reliable operation of Turkey's power system and electricity markets considering large-scale wind power integration. WindFlag aims to solve relevant challenges of large scale OWPP deployment and integration into the Turkish grid, such as extreme weak-grid situations, islanding conditions, and large harmonics and resonances.

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.