Abstract
In recent years, renewable energy sources have been integrated on a
large scale in power systems all around the world to address the
environmental sustainability concerns. With conventional thermal
generators being phased out, large offshore wind power plants present a
viable alternative to provide blackstart services for power system
restoration. In this paper, by means of simulations, grid-forming wind
turbines are shown to successfully energize the offshore transformer and
the HVDC export link in a controlled manner, to ultimately supply the
onshore grid. Two methods for energizing the offshore network have been
compared:
the prevalent hard-switching approach and the more complex soft-start
method. Additionally, control has been implemented to mitigate the
significant transients in the export link associated with pre-charging
of the onshore converter. It is shown that soft-start can provide faster
energization with smaller transients compared to hard-switching.
Moreover, the sensitivity analyses performed
in this study illustrate the impact of pre-insertion resistor design and
voltage ramp-up rates on transients during hard-switching and
soft-start, respectively. The results presented in the paper also show
that a separate controlled pre-charging stage of the onshore converter
from its DC terminals is essential for the safe energization and
operation of the export link.
The manuscript has been accepted for publication in IET Renewable Power
Generation.