Topics: Electric power, Direct current, Electric power transmission Pages: 16 (3070 words) Published: February 15, 2013
Journal of Theoretical and Applied Information Technology
© 2008 JATIT. All rights reserved.



S. Tara Kalyani, 2G. Tulasiram Das
Associate professor, Department of Electrical Engineering,
Jawaharlal Nehru Technological University, Hyderabad, India -500085; 2
Professor, Department of Electrical Engineering,
Jawaharlal Nehru Technological University, Hyderabad, India -500085; E-mail:,

The Unified Power Flow Controller (UPFC) is the most versatile and complex power electronic equipment that has emerged for the control and optimization of power flow in electrical power transmission system. This paper presents real and reactive power flow control through a transmission line by placing UPFC at the sending end using computer simulation. When no UPFC is installed, real and reactive power through the transmission line can not be controlled. This paper presents control and performance of UPFC intended for installation on that transmission line to control power flow. A control system which enables the UPFC to follow the changes in reference values like AC voltage, DC voltage and angle order of the series voltage source converter is simulated. In this control system, a generalized pulse width modulation technique is used to generate firing pulses for both the converters. Installing the UPFC makes it possible to control an amount of active power flowing through the line. Simulations were carried out using MATLAB and PSCAD software to validate the performance of the UPFC. Keywords: DC voltage regulation, Flexible AC Transmission Systems (FACTS), feed back control, high power PWM converters, real and reactive power, Unified Power Flow Controller (UPFC).

The improvements in the field of power
electronics have had major impact on the
development of the concept itself.
A new
generation of FACTS controllers has emerged with
the improvement of Gate Turn-Off (GTO)
thyristor ratings (4500V to 6000V, 1000A to
6000A). These controllers are based on voltage
source converters and include devices such as
Static Var Compensators (SVCs), Static
Thyristor Controlled Series Compensators
(TCSCs), the Static Synchronous Series
Compensators (SSSCs), and the Unified Power
Flow Controllers (UPFCs).
The UPFC is the most versatile and complex of
the FACTS devices, combining the features of the
STATCOM and the SSSC. The UPFC can
provide simultaneous control of all basic power
system parameters, viz., transmission voltage,
impedance and phase angle. It is recognized as the
most sophisticated power flow controller currently,
and probably the most expensive one.

Today’s power systems are highly complex and
require careful design of new devices taking into
consideration the already existing equipment,
especially for transmission systems in new
deregulated electricity markets. This is not an
easy task considering that power engineers are
severely limited by economic and environmental
issues. Thus, this requires a review of traditional
methods and the creation of new concepts that
emphasize a more efficient use of already existing
power system resources with out reduction in
system stability and security. In the late 1980s, the
Electric Power Research Institute (EPRI)
introduced a new approach to solve the problem of
designing and operating power systems; the
proposed concept is known as Flexible AC
Transmission Systems (FACTS) [1]. The two
main objectives of FACTS are to increase the
transmission capacity and control power flow over
designated transmission routes.

Journal of Theoretical and Applied Information Technology
© 2008 JATIT. All rights reserved.

regulate the current flow, and hence the power
flow on the transmission line.

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