Download A Simple Control Technique For Unified Power Flow Controller

ISSN 2230- 9373
Volume-VII, Issue-1
January-March, 2017
A Simple Control Technique For Unified
Power Flow Controller (UPFC)
1.Satyaranjan Das 2. Bhagbat Panda 3.P.C.Panda
Ph.D. Scholar 2Professor, School of Electrical Engineering, KIIT, Bhubaneswar 3Professor, School of Electrical Engineering KIIT,
Bhubaneswar
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Abstract
The paper suggest the better application of UPFC over
STATCOM and SSSC in terms of reactive power
compensation, voltage stability and control in a power
system. The main advantage of the UPFC in three phase
line compensation is integrated in to a Unified or
Generalised power flow controller. This paper describes
the simple technique of controlling real and reactive
power flow & a comparative study between the
conventional power flow controllers like STATCOM &
SSSC with UPFC. This paper suggests a simulation
study of all the controllers individually through
MATLAB simulation tool.
I.
INTRODUCTION
fall where as an increase of reactive power margin
causes a rise of system voltage.[1]-[2]
Generally, voltage stability problem occurs due to
change of reactive power availability in the power
system. Therefore, FACT devices are used to
maintain the voltage profile and control the
availability of reactive power in a power system.
The Unified power flow controller (UPFC) is used
for dynamic control & compensation of power flow
in ac transmission system. It consists of two different
switching converters basically voltage source
inverters regulated with GTO valves as illustrated in
figure-1 given below.
Now-a-days, different power electronics based
technologies are used to facilitate the flow of large
amount of power. These electronic devices are called
Flexible AC Transmission [FACT] devices. These
devices generally based on power electronics
converters & they will provide the facility of quick
and flexible control of power flow in power system.
Many devices are there to contribute reactive power
compensation and in maintaining voltage profile.
Under light load condition, the transmission line
delivers reactive power where as the transmission
line absorbs or consumes the reactive power under
heavy load condition. Therefore, the power flow can
be controlled by controlling the reactive power flow
in the transmission line of power system. So a
decrease of reactive power margin may cause voltage
The inverters named as Inverter-1 and Inverter-2 in
above figure is linked with each other by a dc link
with respect through dc capacitor. This type of
network works as a power converter to covert ac to
ac and real power can flow in both direction, where
both inverter can independently produce or receive
reactive power across its terminal.
Journal of Engineering Innovation and Research, Volume-VII, Issue-1, January-March 2017
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The Inverter-2 supplies an ac voltage Vpq such that
0<Vpq<Vpqmax and conduction angle δ such that 0< δ
<3600 at the considered power frequency. The line
current starts flowing through this voltage source by
creating overall control of real and reactive power in
power system.[1]
with line current I. In figure-2(c), where Vpq=Vδ is
injected with an angle δ as phase shift with respect to
Vδ. Figure-2(d) represents multi-function power flow
control, which is executed by simultaneous terminal
voltage regulation along with series capacitive line
compensation and phase shifting.[1]
The main objective to use Inverter-1 is to control the
real power demanded by Inverter-2 at the common dc
link. This power at DC link is then converted to AC
again and then fed to the system through shunt
connected transformer. The Inverter-1 provides shunt
compensation of reactive power for the transmission
line. This set up may not support the continuous flow
of reactive power through UPFC.[3]
Vpq = Vc+Vδ+ΔV
The UPFC helps in series and shunt compensation
along with phase shifting during power transmission
by adding or injecting voltage Vpq with terminal
voltage Vo.
Overall, we can assume that the UPFC has a greater
control over the angular position and magnitude of
voltage injected in real time so as to control the real
and reactive power flow as demanded by the load in
power system. In the following section, this paper
illustrates a comparative study of real and reactive
power flow through UPFC, SSSC and STATCOM
through MATLab simulation on a 500KV, MVA
system operated with a frequency of 60Hz system.
The proposed model is a 48-Pulse GTO based UPFC
(500KV, 100MVA). The UPFC is used between two
Buses B1 and B2 which control the power flow
through Bus B2 by controlling the voltage of Bus B1.
The converter pair operates in different modes. The
shunt converter works as a STATCOM by controlling
voltage and VAR compensation. Whereas the series
converter operates as SSSC by controlling the
voltage injected in quadrature with current.[1]
II. UPFC CONTROL
The phasor representation of basic UPFC function
may be illustrated as follows.
Figure-2- Basic UPFC control functions: (a) voltage regulation (b) series
compensation (c) angle regulation (d) multi-function power flow control (e)
block diagram of UPFC
Series capacitive compensation as shown in above
figure-2(b) where Vpq=Vc is injected in quadrature
When two converters are used in UPFC mode, the
series converter operates as SSSC where as the shunt
converter operates as STATCOM which controls the
voltage at Bus B1 by controlling the reactive power
by either generating or absorbing to it. It allows the
active power to flow in series converter through DC
bus. The overall control of reactive power is obtained
by changing the DC bus voltage.
At normal power flow, when UPFC is absent, then
zero voltage is injected through bus B2 by the series
converter, where as in the presence of UPFC, both
magnitude & phase of the voltage injected in series
can be varied as a result, the real and reactive power
can be controlled. When the injected voltage attends
its maximum value (0.1PU) and the phase angle is
varied from 00 to 3600, then we will get the
controllable region for UPFC.
Journal of Engineering Innovation and Research, Volume-VII, Issue-1, January-March 2017
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III. UPFC controllable region
IV. SIMULATION FINDINGS
SSSC VOLTAGE INJECTION
STATCOM [VOLTAGE CONTROL] + SSSC
[VOLTAGE INJECTION]
STATCOM [VAR COMPENSATION]
UPFC [POWER FLOW CONTROL]
STATCOM [VOLTAGE CONTROL]
Journal of Engineering Innovation and Research, Volume-VII, Issue-1, January-March 2017
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V. ANALYSIS
The simulation results suggest the following
outcomes. Initially, the real and reactive power
reference values are Pref= +8.7PU/100MVA
(+870MW) and Qref = -0.6PU/100MVA
(-60MVAR) respectively. But at time 0.25sec
Pref value is changing to +10PU (+1000MW),
which is suggesting the rise of real power flow
during UPFC mode control system. Then after
time 0.5sec, Qref value is changing to +0.7PU
(+70MVAR), which is suggesting the reactive
power compensation during UPFC mode control
system. During UPFC mode operation, the series
injected voltage magnitude due to which the
reactive power is compensating, can be
controlled by varying the conduction angle.
VI. CONCLUSION
In comparisons with conventional FACT devices,
UPFC provides dynamic control of line parameters,
which results the smooth and effective control of
power flow. The Unified Power Flow Controller may
also be used primarily as generalised power flow
controller which is capable of maintaining the
required real and reactive power flow at the
respective buses of ac line. A better flexibility in
controlling ac power transmission of STATCOM and
SSSC can be achieved through UPFC in a power
system.
UPFC", 2015 International Conference on Electrical and
Information Technologies (ICEIT), 2015.
[5] Edris, A. Mehraban, A.S., Rahman, M., Gyugyi,
L.,Arabi, S., Rietman, T.,'Cotnrolling the Flow of
Real and Reactive Power', IEEE Computer
Application in Power, January 1998, p. 20-25
[6] C.Su and Z.Chen, “Damping Inter-Area oscillations
using static synchronous series compensator (SSSC)”,
Universities’ Power Engineering Conference, 2011.
[7] N.Mithulananthan, C.A.Canizares, J.Reeve and
G.J.Rogers, “Comparison of PSS, SVC and STATCOM
Controllers for damping power system oscillation”, IEEE
Trans., Vol.18, No.2, May 2003.
[8] T.Nireekshana,Dr.G.K.Rao and Dr.S.S.N.Raju,
“Modelling & control design of unified power flow
controller for various control strategies”, International
Journal
of
Engineering
Science
&
Technology,Vol.2,No.11,pp.6293-6307,2010.
Satyaranjan Das is working as
Asst.
Professor
in
the
Department
of
Electrical
Engineering at Ajay Binay
Institute
of
Technology,
Cuttack. His area of research
includes
Power
Quality
Conditioning, Power Flow
Control in Power System. He
can be contacted at [email protected]
VII. REFERENCES
[1] Gyugyi L, Schauder CD, Torgerson SL, Edris A. The
unified power flow controller: a new approach to power
transmission control. IEEE Trans Power Delivery
1995;10(2):1085–97.
[2] Hingorani NG, Gyugyi L. Understanding FACTS
concepts and technology of flexible AC transmission
systems. IEEE Press; 2000.
[3] Rakhmad Syafutra Lubis. "Digital simulationof the
FACTS system with 60-pulse GTO based Voltage Source
Converter", 2011 2nd International Conference on
Instrumentation Communications Information Technology
and Biomedical Engineering, 11/2011
[4] Djilani Kobibi, Youcef Islam, Samir Hadjeri, and
Mohammed Abdeldjalil Djehaf. "Independent Power Flow
Control and dynamic performance enhancement by the
Journal of Engineering Innovation and Research, Volume-VII, Issue-1, January-March 2017
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