09-07-2012, 01:24 PM
VSC-Based HVDC Power Transmission Systems: An Overview
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INTRODUCTION
HVDC POWER transmission systems and technologies
associated with the flexible ac transmission system
(FACTS) continue to advance as they make their way to commercial
applications [1]–[30]. Both HVdc and FACTS systems
underwent research and development for many years, and they
were based initially on thyristor technology and more recently
on fully controlled semiconductors and voltage-source converter
(VSC) topologies [1]–[30]. The ever increasing penetration of
the power electronics technologies into the power systems is
mainly due to the continuous progress of the high-voltage highpower
fully controlled semiconductors [31]–[36].
CSC-HVDC SYSTEM CONFIGURATIONS
Depending upon the function and location of the converter
stations, various configurations of HVdc systems can be identified.
The ones presented in this section involve CSC-HVdc
configurations but similar types of configurations exist for VSCHVdc
with or without transformers depending upon the project
in question.
VSC-HVDC FUNDAMENTAL CONCEPTS
A basic VSC-HVdc system comprises of two converter stations
built with VSC topologies (see Fig. 2). The simplest VSC
topology is the conventional two-level three-phase bridge shown
in Fig. 7.
Typically, many series-connected IGBTs are used for each
semiconductor shown (see Fig. 7) in order to deliver a higher
blocking voltage capability for the converter
VSC-HVDC MULTILEVEL TOPOLOGIES
In this section, different selected VSC topologies suitable
for the implementation of a VSC-HVdc system are discussed.
Multilevel converters extend the well-known advantages of
low- and medium-power PWM converter technology into the
high-power applications suitable for high-voltage high-power
adjustable-speed drives and large converters for power systems
through VSC-based FACTS and HVdc power transmission
[70]–[86].