21-09-2012, 03:50 PM
Study of UPFC Location for Installing in Power System to Control Power Flow
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Abstract:
This research studies the effect of location of Unified Power Flow Controller (UPFC) on power
system. In this study the several case studies including various points for installing UPFC on power system are
considered and results of profile of voltage at all of buses of system is obtained. The active and reactive of all
transmission lines of power system following installing UPFC at various points of system is discussed and
results are analyzed. The encouragement to the construction of HV lines, the amount of power transmission/km
on HV line and the amount of power transaction as seen from economic side is much responsible for concern
towards congestion in power system. The solution is the use of FACTS devices especially the use of UPFC.
In this research the study of UPFC with its various candied locations for installing on power system is
understood. Second, the operation of control system used in its converters is also studied. Finally by help of
modeling of a power system in MATLAB/SIMULINK, and by installing UPFC in transmission link, its use as
power flow controller and voltage injection is seen. Conclusion is made on different results to see the benefit
of UPFC in power system.
INTRODUCTION
The ongoing deregulation of power systems around
the world may not only bring cheaper electricity and
better service to the customers but also present new
technological challenges to the power industries and
researchers. In a deregulated environment, the open
access to the transmission networks requires adequate
Available Transfer Capability (ATC) to guarantee
economic transactions (Carsten, 2002). However, in a
privatized electricity market, the major traditional ways to
enhance ATC, such as rescheduling active power
generations, adjusting terminal voltage of generators, and
changing taps of on-load tap changer, etc, may not be
centrally controlled by the transmission network owner or
system operator. Construction of new transmission lines
has always been an option, but it is subject to tougher and
tougher environmental restrictions and sometimes social
problems too (Enrique et al., 2004). Besides, it is quite
expensive to construct new transmission lines, which is
not profitable for the network owners. Thus, effective
utilization of the existing transmission systems with the
help of new technologies will be a choice in many power
systems in the world (Taranto et al., 1992).
UNIFIED POWER FLOW CONTROLLER
Line outage, congestion, cascading line tripping,
power system stability loss are the major issues where
capability and utilization of FACTS are noticed.
Representative of the last generation of FACTS devices is
the Unified Power Flow Controller (UPFC). The UPFC is
a device which can control simultaneously all three
parameters of line power flow (line impedance, voltage
and phase angle). Such "new" FACTS device combines
together the features of two "old" FACTS devices
(Venkataraman, 2002; Peng et al., 2004): The Static
Synchronous Compensator (STATCOM) and the Static
Synchronous Series Compensator (SSSC). In practice,
these two devices are two Voltage Source Inverters
(VSI’s) connected respectively in shunt with the
transmission line through a shunt transformer and in series
with the transmission line through a series transformer,
connected to each other by a common dc link including a
storage capacitor. The shunt inverter is used for voltage
regulation at the point of connection injecting an
opportune reactive power flow into the line and to balance
the real power flow exchanged between the series inverter
and the transmission line.
UPFC CONTROL SYSTEM
In order to understand the UPFC Control System the
phasor diagram in the Fig. 2 and 3.
This FACTS topology provides much more flexibility
than the SSSC for controlling the line active and reactive
power because active power can now be transferred from
the shunt converter to the series converter, through the
DC bus. Contrary to the SSSC where the injected voltage
Vs is constrained to stay in quadrature with line current I,
the injected voltage Vs can now have any angle with
respect to line current. If the magnitude of injected
voltage Vs is kept constant and if its phase angle with
respect to V1 is varied from 0 to 360 degrees, the locus
described by the end of vector V2 (V2=V1+Vs) is a circle
as shown on the phasor diagram. As is varying, the phase
shift * between voltages V2 and V3 at the two line ends
also varies. It follows that both the active power P and the
reactive power Q transmitted at one line end can be
controlled. The shunt converter operates as a STATCOM
(Teerathana et al., 2005).
SIMULATION AND RESULTS
Using the concept of the control system a power
system is taken to implement the use of UPFC. The two
modes i.e. the power flow control and the voltage
injection mode are simulated in SIMULINK to see the
effect of UPFC on a power system. Study is carried out to
verify the utility of FACT device. The Fig. 5 illustrates
application study the steady-state and dynamic
performance of a unified power flow controller (UPFC)
used to relieve power congestion in a transmission
system. The load flow analysis and the single line diagram
simulation are done on power flow simulator. This
software helps to calculate the power flow, the voltage at
each bus and the cost effectiveness of the system.
CONCLUSION
In power system transmission, it is desirable to
maintain the voltage magnitude, phase angle and line
impedance. Therefore, to control the power from one end
to another end, this concept of power flow control and
voltage injection is applied. Modeling the system and
studying the results have given an indication that UPFC
are very useful when it comes to organize and maintain
power system. In this study the effects of UPFC locations
are investigated on voltage profile and transmission lines
power flow as active and reactive power are analyzed.