International Journal of Advanced Technology & Engineering Research (IJATER)

RECENT ADVANCES IN HIGH-VOLTAGE DIRECT-

CURRENT POWER TRANSMISSION SYSTEM
K. Pawani, RIT, Raipur, Pawani60_pantnaik@yahoo.co.in1; Sachidanand Ojha, Mahatma Gandhi Chitrakoot Gramodaya Viswavidyalaya
Chitrakoot, satna (M.P), sd_ojha@yahoo.co.in 2; Rama Mishra, M.E IVsem, RIT, Raipur, mishrarama02@gmail.com3

1. Line-commutated current-source converters (CSCs) using

Abstract thyristor. This technology is well established for high
power, typically around 1000MW, with the largest project
The ever increasing progress of high-voltage high-power being the Itaipu system in system in Brazil at 6300MW
fully-controlled semiconductor technology continue to have power level.
a significant impact on the development of advance power
electronic apparatus used to support optimized operation and
efficient management of electrical grids, which in many cas-
es are fully or partially deregulated networks. Developments
advance both the high voltage direct-current (HVDC) power
transmission and the flexibility alternating current transmis-
sion system (FACTS) technologies. In this paper, an over-
view of the recent advances in the area of voltage source
converter (VSC) HVDC technology is provided. Selected
key multilevel converter topologies are presented. Control &
modeling method are discussed. It is confirmed that the con-
tinuous development of power electronics present cost effec- Figure 1: HVDC system based on CSC technology with thyris-
tors
tive opportunities for the utilities to exploit and HVDC re-
mains a key technology. In particular, VSC-HVDC can ad-
2. Forced-commutated voltage-source converter(VSCs) us-
dress not only conventional network issues such as bulk
ing gate-turn-off thyristor (GTOs) or in most industrial
power transmission, asynchronous network interconnection,
cases insulated gate bipolar transistor(GTOs) or in most
back-to-back AC system linking and voltage/stability sup-
industrial cases insulated gate bipolar transistors(IGBTs).
port to mention a few, but also niche markets such as the
It is well established technology for medium power levels
integration of large scale renewable energy sources with the
thus far, with the largest size project being the latest size
grid.
project being the latest one named Estlink at 350 MW lev-
el.
Introduction
The fully-controlled semiconductor devices available to-
day for high-voltage high power converter can be either thy-
ristor or transistors. These device can be used for a VSC
with pulse-width modulation (PWM), operating at frequen-
cies higher than the line frequency and self-commuted via
gate pulse.

HVDC and FACTS system are important technologies,

supporting in their own way the modern power system, Figure 2: HVDC system based on VSC technology built with
which in many cases are fully partially deregulated in sever- IGBTs.
al countries. In near future, even higher integration of elec-
trical grids and marked driven development are expected as, 3. The objective of this paper is to provide an overview of
for instance, countries in the Middle-east, China, India and the HVDC technologies. Modeling and control in another
South America require infrastructure to power their growth. area of importance and recent contribution presented in
the technical literature are analyzed briefly. Finally,
Today, there are more than 92 HVDC projects worldwide emerging application of VSC-HVDC system and multi-
transmitting more than 75GW of power employing two dis- terminal DC configuration that can be used to interconnect
tinct technologies as follows large scale wind energy sources with the grid discussed.

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 International Journal of Advanced Technology & Engineering Research (IJATER)

The advantage of such system is that one pole can contin-

HVDC System Configuration ue to transmit power in the case that the other one is out of
service for whatever reason. In other words, each system can
Depending upon the function and location of the converter operate on its own as an independent system with earth re-
stations, various configurations of HVDC configuration but turn.
similar type of configuration but similar type of configura-
tion exist for VSC-HVDC with or without transformers de-
pending upon the project in question.

A. Back-to-Back HVDC system

In this case, the two converter station is located at same site
and there in no transmission of power with a DC link over a
long distance. The two AC system interconnected may have
the same or different frequency.

Figure 5: Bipolar CSC-HVDC system with one 12-pulse con-

verter per pole.

D. Multi-terminal HVDC system

In this configuration there are more than two sets of
converter like the bipolar version. In this converter 1 and 3
Figure 3: Back-to-back CSC-HVDC system with 12-pulse con-
can operates as rectifier while converter 2 operates as
verters. inverter. Working in other order, converter 2.

B. Monopolar HVDC System

In this Configuration, two converter are used which are
separated by a single pole line and a positive or a negative
DC voltage is used,Many of the cable transmission with
submarine connection use monopolar system. The ground in
used to return current.

Figure 6: Multi-terminal CSC-HVDC system parallel con-

nected.

VSC-HVDC Fundamental Concepts

A basic VSC-HVDC system comprises of two converter
Figure 4: Monopoolar CSC-HVDC system with 12 pulse con- station built with VSC topologies. Typically, many series
verters. connected IGBT are used for each semiconductor. In order
to deliver a higher blocking voltage capability for the con-
C. Bipolar HVDC System. verter and therefore increase the DC bus voltage level of the
converter and therefore increase the DC bus voltage of the
This is the most used configuration of a CSC-HVDC sys- HVDC system.
tem in application where overhead lines are used to transmit
power. In fact, the bipolar system is two monopolar system.

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 International Journal of Advanced Technology & Engineering Research (IJATER)

Multilevel VSC Topologies For HVDC

In this section, different selected VSC topologies
suitable for the implementation of a VSC-HVDC
system are discussed. Multilevel converter extend
the well-known advantage of low and medium
power PWM converter technology into the high
power application suitable for high-power adjust-
able speed drive and large converter for power
Figure 7: Conventional two-level VSC three-phase topology. system through FACTS and VSC-based HVDC
The converter is typically controlled through sinusoidal power transmission.
PWM (SPWM) and the harmonics are directly associated
with the switching frequency of each converter. Filter are
also include on the AC side to further reduce the harmonics
content flowing into the AC SYSTEM.

Figure 9: Five- level flying capacitor VSC phase leg topology

Modelling And Control

Recently, a dynamic model for a back-to-back HVDC
system based on the three-level NPC topology was pre-
sented, Finally, in a control system for the VSC-HVDC dur-
Figure 8: Tow-level sinusoidal PWM method: reference (sinu-
ing island operation and under three-phase balanced fault
soidal) and carrier (triangular) signals and line-to-neutral vol-
tage waveform. was investigated and it has been found that current limit of
the converter s has a significant influence on the dynamic
The use of VSC as opposed to a line commutated CSC offer response of the system.
the following advantage
 Avoidance of commutation failures due to disturbance
in the AC network.
Emerging Applications
 Possibility to connected the VSC-HVDC system to a VSC –HVDC can be effectively used in a number of key
“weak” AC network or even to one where no generation areas as follows
source is available and naturally the short-circuit level is  Power supply to island.
very low.  Remote small-scale generation
 No need of transformer for the conversion process.  Off-shore generation and deep sea crossing
 Multi-terminal systems.

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 International Journal of Advanced Technology & Engineering Research (IJATER)

From the technology point of view, wind farm and off-shore

wind farms in particular are well-suited for VSC-HVDC
application.

VSC-HVDC Worldwide Installation

In this section, the various projects worldwide where
VSC-based HVDC systems have been successfully exploited
are discussed. They involve Back-to-back system (Eagle
pass, USA), wind energy application (Gotland, Sweden),
Power enhancement (Crosssound link, USA). It should be
noted that the DC voltage has reached ±150KV and the larg-
est system is at 350MW, making the VSC-HVDC a well
established technology in the medium power levels.

Conclusion
In this paper, advances of the VSC-HVDC technology are
presented. the key benefits include independent control of
active and reactive power through the PWM control of the
converter. It is confirmed that development associated with
VSC-HVDC technologies have deliver system at voltage
level up to ±150kv and power level up to 350MW.

References
[1] K.R. Padiyar, “HVDC power transmission system;
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[2] J.Arrillaga, “ High voltage direct current transmission
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0852969414, October 1998.
[3] Y.H. and A. T. Johns, “Flaxible AC transmission sys-
tem (FACTS) “, Institution of electrical Engineers,
ISBN: 0852967713, November 1999.
[4] E.Acha, V.G. Agelidis,O. Anaya-Lara and T.J.E. Mil-
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[5] R.M. Mathur and R.K. Varma, “ Thyrister-Based
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[6] L.Gyugyi, “Reactive power generation and control by
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