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Abstract of Dissertation presented to COPPE/UFRJ as a partial fulfillment of the
requirements for the degree of Master of Science (M.Sc.)
A BIDIRECTIONAL LOAD FLOW HVDC TAP STUDY
Felipo Corrêa Machado
September/2006
Advisor: Maurício Aredes
Department: Electrical Engineering
The unidirectional load flows HVDC Tap models provide access to small sized
and medium sized consumers to HVDC System in any point of the dc link, which
may have their loads supplied by the HVDC Tap with no influence in its operation.
The present work intends to present a proposal of a new HVDC Tap with a topology
which allow not only consumers but also generators to connect themselves to the
HVDC System and perform an interchange of power with it, not characterizing
the HVDC Systems as point-to-point transmissions. The local ac system can be
isolated or be connected to any other ac system in which the HVDC Tap must be
synchronized.
The new topology intends to keep the same level of reliability and original
stability with the HVDC System that it will be connected. In the Bidirectional
HVDC Tap high voltage circuit, there are three H-Bridges in series with the dc link.
To compose each H-Bridge, four GTO are disposed in order to allow the control of
the current in the passive elements of H-Bridge. The power is about 5 % of the dc
link power, which justify the type of connection proposed to this converter.
To compose the three phase voltage, the secondary of the transformers are
connected in Y. The dc-ac converter changes the continuous current in three phase
voltage using PWM techniques to deliver to the ac system energy with quality. For
this porpouse, the control of each H-Bridge controls the secondary voltages acting
in the reference of current to be applied in the primary of the transformers. The
complete system, embracing the HVDC system, the Bidirectional HVDC Tap and
ac system, is modelated in the PSCAD simulator, where the results were obtained
from.
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