xDFM vs FULL CONVERTER
POWER
QUALITY
Within xDFM topology, THD
is controlled bellow 1% without harmonics filter need.
Within Full Converter topologies, THD is quite high (typically beyond 5%) and harmonics filters are completely necessary as all the power is delivered to the grid through the power converter.
Within Full Converter topologies, THD is quite high (typically beyond 5%) and harmonics filters are completely necessary as all the power is delivered to the grid through the power converter.
GRID
CODES FULFILMENT
Within xDFM topology, in case
any fault occurs in the grid, the system provides higher current capacity
than Full-converter topologies. This current capacity that can reach 5xIn
(five times the rated current) is useful for contributing to trip over-current
protections and clear the fault.
Within Full Converter topologies, this current capacity is typically limited to 2xIn (twice the rated current).
Within Full Converter topologies, this current capacity is typically limited to 2xIn (twice the rated current).
MECHANICAL LOADS
Within Full Converter topologies damping to reduce mechanical loads is possible. However, in emergency situations, converter may be disconnected from the grid and damping is disabled due to lack of voltage.
HVDC CONNECTION
The xDFM topology is also
suitable for high voltage DC link transmission (HVDC) in variable speed generation
systems. As shown below, the DC output can be produced by using a high voltage
generator with a rectifier or with a low voltage generator and an additional
transformer with one or more taps, where in each secondary is rectified and
all of such rectifiers are connected in series or parallel.
The output of the AC voltage can be controlled to have constant power and frequency, allowing a am optimum sizing of required rectifiers and transformers and reducing the ripple content of the DC output voltage under low wind conditions, improving the output power quality.
Within Full Converter topologies HVDC connection is not cost effective at all.
The output of the AC voltage can be controlled to have constant power and frequency, allowing a am optimum sizing of required rectifiers and transformers and reducing the ripple content of the DC output voltage under low wind conditions, improving the output power quality.
Within Full Converter topologies HVDC connection is not cost effective at all.
COST
The cost of the wind turbines based on xDFM topologies is lower than Full Converter ones.
In Full Converter, the power converter must be sized to transfer the total current, while in case of xDFM only about 30% of current, as a maximum, is managed by the power converter.
In case the stator of the Doubly Fed Induction Generator (DFIG) was designed for medium voltage grid connection, even the transformer could be saved.
In Full Converter, the power converter must be sized to transfer the total current, while in case of xDFM only about 30% of current, as a maximum, is managed by the power converter.
In case the stator of the Doubly Fed Induction Generator (DFIG) was designed for medium voltage grid connection, even the transformer could be saved.