IJSRD Found one good reserch article on Electrical Engineering Department
Abstract— This paper is based on Occurrence of a fault in a
power system causes transients. To stabilize the system, The
Flexible Alternating Current Transmission (FACTS) devices
such as UPFC are becoming important in suppressing
power system oscillations and improving system
damping. The UPFC is a solid-state device, which can be
used to control the active and reactive power.. By using a
UPFC the oscillation introduced by the faults, the rotor
angle and speed deviations can be damped out quickly than
a system without a UPFC. The effectiveness of UPFC in
suppressing power system oscillation is investigated by
analyzing their oscillation in rotor angle and change in
speed occurred in the two machine system considered in
this work. A proportional integral (PI) controller has been
employed for the UPFC. It is also shown that a UPFC can
control independently the real and reactive power flow in a
transmission line. A MATLAB simulation has been carried
out to demonstrate the performance of the UPFC in
achieving transient stability of the two-machine five-bus
system.
I. INTRODUCTION
The UPFC is the most versatile of the FACTS devices.
The main function of the UPFC is to control the flow
of real and reactive power by injection of a voltage in
series with the transmission line. Both the magnitude and
the phase angle of the voltage can be varied
independently. Real and reactive power flow control
can allow for power flow in prescribed routes, loading of
transmission lines closer to their thermal limits and can
be utilized for improving transient and small signal
stability of the power system.
Fig. Schematic diagram of UPFC
The UPFC consists of two branches. The series branch
consists of a voltage source converter, which injects a
voltage in series through a transformer. The inverter at the
input end of the UPFC is connected in shunt to the AC
power system and the inverter at the input end of the UPFC
is connected in series with the AC transmission circuit.
Since the series branch of the UPFC can inject a voltage
with variable magnitude and phase angle it can
exchange real power with the transmission line. However
the UPFC as a whole cannot supply or absorb real power in
steady state (except for the power drawn to compensate
for the losse.
The Unified Power Flow Controller (UPFC) was
proposed' for real turn-off time control and dynamic
compensation of ac transmission systems, providing the
necessary functional flexibility required to solve many of
the problems facing the utility industry. The Unified Power
Flow Controller consists of two switching converters,
which in the implementations considered are voltage
sourced inverters using gate thyristors valves, as
illustrated in Fig. These inverters, labeled "Inverter1" and
"Inverter 2" in the figure, are operated from a common dc
link provided by a dc storage capacitor.
This arrangement
functions as an ideal auto ac power converter in which the
real power can freely flow in either direction between the
ac terminals of the two inverters and each inverter can
independently generate (or absorb) reactive power at its
own ac output terminal since the series branch of the UPFC
can inject a voltage with variable magnitude and phase
angle it can exchange real power with the transmission line.
However a UPFC as a whole cannot supply or absorb real
power in steady state (except for the power drawn to
compensate for the losses). Unless it has a power source at
its DC terminals. Thus the shunt branch is required to
Transmission Line
Shunt Transformer
VSC2 VSC1
Control
Transient Stability of Power System Using Facts Device-UPFC
(IJSRD/Vol. 1/Issue 3/2013/0025)
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compensate (from the system for any real power
drawn/supplied by the series branch and the losses. if the
power balance is not maintained, the capacitor cannot
remain at a constant voltage. Shunt branch can
independently exchange reactive power with the system.
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