The Effect of Different Filters Connected to DC-DC converters in multi-terminal HVDC System for Offshore Wind Farms

There is increasing interest in interconnecting individual wind
turbines in offshore wind farms using DC networks rather
than AC networks. As the output from each turbine/generator
is normally low (less than 6 kV), DC-DC converters may be
required to step-up the voltage to an intermediate level to
interconnect the turbine outputs, and another DC-DC
converter to step-up this intermediate voltage to a high level
for transmission to the shore.
One possible structure of the transmission side of the multiterminal
system is radial topology with tens or hundreds of
submodules, as shown in Figure 1.
Each of the submodules is combined with a permanent
magnet synchronous generator, a PWM rectifier and a DCDC
converter. Filters are required to achieve relatively
smooth output DC waveforms at each stage: these filters
between the PWM rectifiers and the DC-DC converters play
an important role during the operation. This paper will
concentrate on the performance of different types of filters
and their influences on the sending end of the system, while
the most suitable structures of the filter will be proposed.