In the next years, several offshore wind farms will be installed all over Europe. Due to the technologic advantages that voltage-source converters have when compared to other available options, there is a strong possibility that this will be the technology chosen to connect offshore wind farms. Such assumption intensifies the need of studying and simulating the control methods for these systems. Therefore, the purpose of this work is to present and explain all the models that are needed to simulate, with the necessary detail, the electric systems of the offshore wind farms, the high-voltage converters and the DC grid. The control method of the DC system is given and several methods to control the DC grid voltage are presented and compared. This way, it will be possible for several countries connected to the multi-terminal DC grid not only to receive energy from the offshore wind farms, according to desired criteria, but also to trade energy with other nations.

Electricity transmission began with direct current. In 1880, Edison patented the first DC distribution system. That DC system was vital to broaden the use of his most famous invention, the electric lamp. However, at that time, low-voltage DC was proven inefficient. Despite the success of AC systems, the efforts for the development of practical high-voltage direct current transmission (HVDC) continued. The first HVDC transmission system was built in Sweden, in 1954, using mercury-arc valves. Nowadays, modern voltage-source converters (VSC) have smaller space requirements and improved reliability. VSC-HVDC has brought back the interest in the establishment of DC networks for applications such as DC supergrids and transnational networks for offshore wind farms. The goal of this work is to develop a more straightforward simulation model of VSC-HVDC systems; which can be inputted into simulation software packages and still provide realistic and reliable data on the system operation under all circumstances. The major contribution is the integration of the developed model, representing the whole DC transmission link, with the manifold control strategies possible for this new technology.