Research Journal of Applied Sciences, Engineering and Technology 2(4): 356-361, 2010
ISSN: 2040-7467
© M axwell Scientific Organization, 2010
Submitted Date: April 07, 2010
Accepted Date: May 21, 2010
Published Date: July 10, 2010
Enhancement of Power Quality in 14 Bus System using UPFC
1
S. Muthukrishnan and 2 A. Nirmalkumar
Department of EEE, Anna University, Coimbatore, Tamilnadu
2
Department of EEE, Bannari Amman Institute of Technology, Sathyamangalam, Tamilnadu
1
Abstract: This research deals with digital simulation of 14-bus power system using UPFC to improve the
power quality. The UPFC is also capable of improving transient stability in a power system. It is the most
complex pow er electronic system for controlling the power flow in an electrical power system. The real and
reactive powers can be easily controlled in a power system using a UPFC system. The circuit model for UPFC
is developed using rectifier and inverter circuits. The control angle is varied to vary the real and reactive pow ers
at the rec eiving end. T he M atlab sim ulation results are presented to valida te the m odel.
Key w ords: Compensation, matlab simulink, power quality, statcom, UPFC
INTRODUCTION
The pow er-transfer capability of long transmission
lines are usually limited by large signals ability.
Econom ic factors, such as the high cost of long lines and
revenue from the delivery of additional power, give strong
incentives to explore all economically and technically
feasible means of raising the stability limit. On the other
hand, the develop men t of effective ways to use
transmission systems at their maxim um therma l capability
has caught much research attention in recent years. Fast
progression in the field of power electronics has already
started to influence the pow er indu stry. Th is is one direct
outcome of the concept of Flexible AC Transmission
Systems (FACT S) asp ects, w hich h as becom e feasible
due to the improveme nt realize d in po wer-electronic
devices. In principle, the FACTS devices could provide
fast control of active and reactive power through a
transmission line. The U nified Power-Flow Controller
(UPFC) is a mem ber of the FA CTS family with ve ry
attractive features. This device can independently control
many parame ters, so it is the combination of the
properties of a Static Synchronous Compensator
(STATCOM) and Static Synchronous Series Compensator
(SSSC ) (Schaulder, 1998).
These devices offer an altern ative m ean to mitigate
power system oscillations. Thus, an important question is
the selection of the input signals and the adopted control
strategy for these devices in order to damp power
oscillations in an effective and robust manner. Much
research in this domain has been realized (Mihalic, 1996).
This research shows that UPFC is an effective device to
improve the power quality.
The UPFC parameters can be contro lled in order to
achieve the maximal desired effect in solving first swing
stability problem. This problem appears for bulky power
systems with long transmission lines.
Various methods to reference identification of the
series part, in order to improve the transient stability of
the system based on: “optimal parameters”, “state
variab les”(M acho wski, 1998), and also “injection mod el”
were studied.
This paper is organized as follows. After this
introduction, the principle and operation and the
mathematical equations of a UPFC connected to a
network are presented
MATERIALS AND METHODS
A simplified scheme of a UPFC connected to an
infinite bus via a transmission line is shown in Fig.1. The
UPFC consists of a parallel and series branches, each one
containing a transfo rmer, power-electric converter w ith
turn-off capable semiconductor devices and DC circuit.
Inverter 2 is connected in series with the transmission line
by series transformer. The real and reactive power flows
in the transmission line can be quickly regulated by
changing the magn itude (V b ) and phase angle (* b ) of the
injected voltage produced by inverter 2. The basic
function of inverter 1 is to supply the real power
demanded by inverter 2 through the common DC link.
Inverter 1 can also generate or absorb controllable power
(Gyugyi, 1992). New method for improving transient
stability
is given by Saadate (Gholipour and
Saadate, 2003). Application of UPFC is given by Huang
(2000). Enhancement of transient stability using Fuzzy
control is given by S choder et al. (2000). Comparison of
field results and simulation results of VSI based FACTS
converter is g iven b y Sen and Keri (2003 ).
The curren t throug h the D C link is as follow s:
DC current = (V R - V i ) / R
V R = 1.35 V S cos"
Corresponding Author: S. Muthukrishnan, Department of EEE, Anna University, Coimbatore, Tamilnadu
356
(1)
(2)
Res. J. Appl. Sci. Eng. Technol., 2(4): 356-361, 2010
Fig. 1: UPFC installed in transmission line
Fig. 2a: 14 bus system using UPFC
W here; V R - output of the rectifier
V i - input to the inverter
system is show n if Fig. 2a. An additional load is
connected in parallel with the existing load. The circuit
model of 14-bus network is shown in Fig. 2b. The line
impedance is represented by series RL combination. The
voltage across load I is shown in Fig. 2c. Additional load
is conn ected at t = 0.2 sec. A sag is produced as show n in
Fig. 2c. Th e output voltag e across load 2 is sho wn in
Fig. 2d.
Power system with U PFC is shown in Fig. 3a. UPFC
netwo rk alone is shown in Fig. 3b. It consists of a rectifier
- inverter system. UPFC injects voltage at t = 0.3 sec. The
voltage improves to the normal value as shown in Fig. 3c.
Literature (1) to (10) does not deal with the matlab
simulation of multi bus system using UPFC. An attempt
is made in the present work to model and simulate 14-bus
system with UPFC using matlab.
RESULTS AND DISCUSSION
Digital simulation is done using the blocks of matlab
simulink and the results are presented here. The UPFC
357
Res. J. Appl. Sci. Eng. Technol., 2(4): 356-361, 2010
Fig. 2b: 14 bus network
Fig. 2c: Output voltage across load -1
Fig. 2d: Output voltage across load -2
358
Res. J. Appl. Sci. Eng. Technol., 2(4): 356-361, 2010
Fig. 3a: Circuit diagram with UPFC
Fig. 3b: UPFC Network
359
Res. J. Appl. Sci. Eng. Technol., 2(4): 356-361, 2010
Fig. 3c: Output voltage across load-1 with compensation
Fig. 3d: Output voltage across load-2
Tab le 1: V ariatio n of pow er w ith firin g an gle
Firin g an gle
Sr. No. of inverter
R eal p ow er (k W ) R e ac ti ve p ow e r ( kV A R )
1
120º
310
200
2
180º
354
241
is an improvement in the real and reactive powers through
the transmission line when U PFC is introduced. The
UPFC system has the advantages like reduced
maintanance and ability to control real and reactive
powers. UPFC is capa ble of im proving the pow er qua lity
by injecting the voltage. The simulation results are similar
to the predicted results.
The voltage across load 2 is shown in Fig. 3d. Thus the
UPFC system can improve the voltage at a bus. The
objective of UPFC is to improve the power quality by the
sag. From the Fig. 3c, d, it can be seen that the sag is
mitigated. Variation of power with the variation in the
firing angle of the inverter is given in the Table 1.
REFERENCES
Schau lder,
C.D.,
L.
Gyugyi,
M.R.
Lund,
D .M . Hamai, T.R. Rietman, D.R. Torgerson and A.
Edris, 1198. O peration of Unified Power Flow
Controller (UPFC) under practical constraints. IEEE
Trans. Pow er Del., 13(2): 630-6 39.
Mihalic, R., P. Zunko and D. Povh, 1996. Improvement
of transient stability using unified power flow
controller. IEEE Trans. Power Del., 11(1): 485-492.
Macho wski, J., J. Bialek and J. Bumby, 1998. Power
System Dynam ics and Stability. 1st Edn ., Wiley,
New Y ork. ISBN: 978-0471956433.
Gyugyi, 1992. Unified power-flow control concept for
flexible AC transm ission system . Proc. Inst. Elect.
Eng. C, 139(4): 323-331.
CONCLUSION
In the simulation study, matlab simulink enviroment
is used to simu late the mo del of UPFC connected to a 3
phase system. This paper presents the control and
performance of the UPFC used for pow er qua lity
impro vem ent. Voltage compensation using U PFC is
studied. The voltage compensation using UPFC system is
also studied for 14 bus system. The real and reactive
pow ers increase with the increase in angle of injection.
Simulation results show the effectiveness of U PFC to
control the real and reactive pow ers. It is found that there
360
Res. J. Appl. Sci. Eng. Technol., 2(4): 356-361, 2010
Gho lipour, E. and S. Saadate, 2003. A new method for
improving transient stability of power systems by
using UPFC. Proc. European Pow er Electronics,
Toulouse, France, September 2003.
Huang, Z ., N. Y ix in , C .M . Shen, F.W. Felix, S. Chen and
B. Zhang, 20 00. A pplication of U PFC in
interconnected power systems- modeling, interface,
control strategy and case study. IEEE Trans. Power
Syst., 15(2): 817-824.
Schod er, K., A. Hasanovic and A. Feliachi, 2000.
Enhancing transien t stability using fuzzy control
scheme for the Unified Power Flow Controller
(UPFC) within the Pow er System Toolbo x (PST ).
Proc. Midwest Symp. Circuits Sys., lansing, MI, 3:
1382-1385.
Sen, K.K . and A .J.F. Keri, 2003 . Com parison of field
results and digital simulation results of voltagesourced converter-based FACTS controller. IEEE
Trans. Power Del., 18(1): 300-306.
361