Diminishing of Losses In A Transmission Line By Using UPFC
DIMINISHING OF LOSSES IN A TRANSMISSION LINE BY USING
UPFC
MALATHI.KALYANI
Department of Electrical & Electronics Engineering, Lecturer in GPT Narayan Khed, Medak, Andhra Pradesh, India.
Abstract—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. When no UPFC is
installed, real and reactive power losses in the transmission line can not be controlled. This paper presents control and
performance of UPFC intended for installation on that transmission line to minimize losses. Installing the UPFC makes it
possible to control an amount of active power flowing through the line. Based on the conventional power system state
estimation model, a kind of model for state estimation with UPFC is introduced in this paper, in which power injection
model is used and the affect of UPFC on the power flow is transferred to the two nodes of the corresponding transmission
line. This method can be integrated to the conventional state estimation using MATLAB Programming with the
consideration of UPFC. To show the validity of the proposed techniques a five-bus, and an IEEE-14 bus test power systems
are proposed.
Keywords— Flexible ACTransmission Systems (FACTS), Newton Rapshon Method, Losses Minimization, real and
reactive power, Unified Power Flow Controller (UPFC).
I.
and reactive power flows on a transmission line. So,
there has been increasing interest in the analysis of
UPFC in power system. The UPFC can provide
simultaneous control of all basic power system
parameters (transmission voltage, impedance and
phase angle). The controller can fulfill functions of
reactive shunt compensation, series compensation and
phase shifting meeting multiple control objectives.
From a functional perspective, the objectives are met
by applying a boosting transformer injected voltage
and a exciting transformer reactive current. The
injected voltage is inserted by a series transformer.
A new method is introduced to incorporate UPFC
devices into the power losses minimization. This
paper attempts to deduce the model of power losses
with UPFC using the conventional power load flow
studies by using Newton-Rapshon method. A power
injection model that transfers the affect of UPFC
towards the power flow to the two nodes is presented.
This method can be integrated to the conventional
load flow studies program with the consideration of
UPFC. Furthermore, the results demonstrate that the
model is compared with and with out UPFC using
MATLAB Programming.
INTRODUCTION
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).The
two main objectives of FACTS are to increase the
transmission capacity and control power flow over
designated transmission routes. The improvements in
the field of power electronics have had major impact
on the development of the concept itself. Since the
concept of flexible AC transmission systems
(FACTS) was proposed by Hingorani in the 1860s,
many various FACTS devices have been utilized to
meet a growing demand of the transfer capabilities
due to developing wheeling transactions in the
deregulation
environment.
Some
interesting
applications of FACTS devices can be found to
economic dispatch(ED), AC/DC optimal power flow
(OPF), available transfer capability (ATC), contract
path based electricity trading, and transmission
congestion management. UPFC, a versatile FACTS
device, has the unique capability to control
simultaneously both the voltage magnitude and active
11. Operating Principle of UPFC
The basic components of the UPFC are two Voltage
source inverters (VSIs) sharing a common dc storage
capacitor, and connected to the power System
through coupling transformers. One VSI is connected
to in shunt to the transmission system via a shunt
transformer, while the other one is connected in series
through a series transformer.A basic UPFC functional
scheme is shown in fig.1.
Proceedings of 3rd IRF International Conference .Chennai, 23rd Feb. 2014, ISBN: 978-93-82702-60-3
18
Diminishing of Losses In A Transmission Line By Using UPFC
Fig.2 Mathematical model of UPFC
Psi = -r bs vi vjsin (θij+γ)
Qsi = -r bs vi2 cos γ
Fig.1 Basic functional scheme of UPFC
The series inverter is controlled to inject a
symmetrical three phase voltage system (Vse), of
controllable magnitude and phase angle in series with
the line to control active and reactive power flows on
the transmission line. So, this inverter will exchange
active and reactive power with the line. The reactive
power is electronically provided by the series
inverter, and the active power is transmitted to the dc
terminals. The shunt inverter is operated in such a
way as to demand this dc terminal power (positive or
negative) from the line keeping the voltage across the
storage capacitor Vdc constant. So, the net real power
absorbed from the line by the UPFC is equal only to
the losses of the inverters and their transformers. The
remaining capacity of the shunt inverter can be used
to exchange reactive power with the line so to
provide a voltage regulation at the connection point.
The two VSI’s can work independently of each other
by separating the dc side. So in that case, the shunt
inverter is operating as a STATCOM that generates
or absorbs reactive power to regulate the voltage
magnitude at the connection point. Instead, the series
inverter is operating as SSSC that generates or
absorbs reactive power to regulate the current flow,
and hence the power flows on the transmission line.
The UPFC has many possible operating modes. In
particular the power injection method is used to
increase the active power and reduce the losses in
power system.
Psj = r bs vi vjsin (θij+γ)
Qsj = r bs vi vjsin (θij+γ)
Where,
1
—
Xs
r and γ are the UPFC variables representing the ratio
of series transformer voltage to ith bus voltage in p.u.
and the angle of the series voltage in radians
respectively. The term bs is the susceptance of the
series transformer combined with line susceptance Xs
This relationship puts a constraint on the independent
control of the converters. Nevertheless, the reactive
power of the shunt converter can be controlled
independently for bus voltage or VAR control and the
power flow through the line can be controlled through
r and γ. For a scheduled delivery of power at the
receiving end, r and γ will be fixed. Besides the bus
power injections, it is useful to have expressions for
power flows from both sides of the UPFC injection
model defined. At the UPFC shunt side, the active
and reactive power flows are given as
Pi1 = -r bs vi vj sin (θij+γ) − bs vi vj sin θij
(1)
Qi1 = -r bs vi2 cos γ+Qconv1 – bs vi2+ bs vi vj cos θij
(2)
bs =
Whereas at the series side they are
Pj2 = -r bs vi vjsin (θij+γ) − bs vi vj sin θij
(3)
Qj2 = -r bs vi2 cos γ+Qconv1– bs vi2+ bs vi vj cos θij
(4)
111. Mathematical Model of Upfc
The basic structure and operation of the UPFC can be
represented through the model shown infig.2. The
simple power-injection model is used here where the
series- and shunt converter voltages are replaced by
nodal power injections as shown in Fig 2. The
magnitude and phase angle of the series voltage
produced by the converter and the magnitude and
phase angle of the AC voltage applied across. In the
steady state, the real power flowing through the shunt
converter equals the real power exchanged between
the series converter and the transmission system the
shunt converter can be controlled independently.
The UPFC injection model is thereby defined by the
constant series branch susceptance, bs, which is
included in the system bus admittance matrix, and the
bus power injections Psi, Qsi, Psj and Qsj. If there is
a control objective to be achieved, the bus power
injections are modified through changes of the UPFC
parameters r, γ and Qconv1 . The LF model discussed
here assumes that the UPFC is operated to keep (i)
real and reactive power flows at the receiving bus and
(ii) sending bus voltage magnitude at their
prespecified values Here the Newton-Rapshon
algorithmis used to fing the load flow solution of a
Proceedings of 3rd IRF International Conference .Chennai, 23rd Feb. 2014, ISBN: 978-93-82702-60-3
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Diminishing of Losses In A Transmission Line By Using UPFC
particular system The algorithm for solving a power
flow problem without and with UPFC is implemented
by using the MATLAB programming
Fig.3 Operation Scheme for minimization of losses
CONCLUSIONS
Equations which describe the losses minimization by
using power injection method are obtained. The math
lab results demonstrate the validity of the proposed
UPFC model and the UPFC network-interfacing
algorithm. The total active and reactive power losses
are reduced. There by active power is improved due
to minimization of transmission losses in power
system the transmission and distribution costs are
reduced.
Fig.4 The 14- bus test system
II.
RESULT
ACKNOWLEDGMENT
The IEEE-14 bus test system results are shown in this
table comparison for with out and with UPFC
systems.The active and reactive losses are
reduced.The total losses are compared with placing
UPFC and without UPFC.
I express my sincere thanks to Sri.M.Venkateswara
Rao, Associate professor, Head of Department, E.E.E
Department of EEE, for his valuable guidance and
supervision through out the project work.
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Proceedings of 3rd IRF International Conference .Chennai, 23rd Feb. 2014, ISBN: 978-93-82702-60-3
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Diminishing of Losses In A Transmission Line By Using UPFC
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Proceedings of 3rd IRF International Conference .Chennai, 23rd Feb. 2014, ISBN: 978-93-82702-60-3
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