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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.
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