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1. IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163
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Volume: 01 Issue: 03 | Nov-2012, Available @ http://www.ijret.org 455
ENHANCEMENT OF POWER QUALITY BY UNIFIED POWER QUALITY
CONDITIONER WITH FUZZY-PI CONTROLLERS
Anil Bharati1
, S.K Srivastava2
1
Student of M.tech, 2
Associate Professor, Department of Electrical Engineering, M.M.M Engineering College
Gorakhpur(U.P) 273010, India, aanilbharti@gmail.com ,sudhirksri05@gmail.com
Abstract
The nonlinear characteristics of power electronic devices give rise to two important limitations; they generate harmonics and draw
lagging current from the utility. The UPQC mitigates harmonics and provides reactive power to the power systems network so as to
improve the power factor close to unity. The UPQC is a combination of shunt active and series active power filters connected through
a dc bus. The aim of this paper is to make comparative performance analysis and develop control strategies of UPQC based on fuzzy-
PI controller.
Keywords: - UPQC, POWER QUALITY.
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I. INTRODUCTION
The UPQC is the most versatile and complex of the FACTS
devices, combining the features of the STATCOM and the
SSSC.
Source side Load side
Series transformer
Fig1.Basic line diagram of UPQC
The UPQC can provide simultaneous control of all basic power
system parameters, transmission voltage harmonic
compensation, impedance and phase angle.
2. MATLAB BASED SIMULINK MODEL OF UPQC
The three-phase system shown in Fig. 2 is considered for
verifying the performance of UPQC .Three-phase source
feeding this system at one end.
Fig2. Simulink Block model of UPQC
For the best performance, UPQC is placed at the midpoint of
the system as shown in Fig. 2 UPQC is placed between two
sections B1and B2 of the transmission line
3. PERFORMANCE OF UPQC WITH PI
CONTROLLER
When PI based controller is used, the dc link voltage is sensed
at regular intervals and is compared with a reference value. The
Shunt
transformer
DC
Link
PWM
Voltage
Control
PWM
Curren
t
Control

2. IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163
__________________________________________________________________________________________
Volume: 01 Issue: 03 | Nov-2012, Available @ http://www.ijret.org 456
error signal thus derived is processed in a PI controller. A limit
is put on the output of the controller to ensure that the shunt
active power filter supplies active power of the load through the
series active power filter
The STATCOM model in UPQC is connected in shunt with
transmission line using step down transformer. The voltage can
be regulated to improve the voltage stability of the power
system. Thus the main function of the STATCOM is to regulate
key bus voltage magnitude by dynamically absorbing or
generating power to the ac transmission line.
The SSSC which is connected by series transformer with
transmission line generates three-phase voltage of controllable
magnitude and phase angle. This voltage injection in series
with the transmission line is almost in quadrature with the line
current and hence emulates an equivalent inductive or
capacitive reactance in series with the transmission line. A
small part of this injected voltage is in phase with the
transmission line current supplying the required losses in the
Inverter Bridge and transformer.
Simulation Results of UPQC Using PI Controller:-An ideal
three-phase sinusoidal supply voltage of 11kV, 50Hz is applied
to the non-linear load (diode rectifier feeding an RL load)
injecting current harmonics into the system. Fig. 3.(a) shows
supply current in three phase before compensation from 0s to
0.1s, and after compensation from 0.1s to 0.4s. Shunt inverter is
able to reduce the harmonics from entering into the system.
Fig 3(a) source voltage
Fig 3(b) Source current
Fig 3(c) load voltage
Fig 3(d) load current
Fig 4(a) Distorted source current THD=30.7%
Fig 4(b) Compensated source current THD=3.94%
0 0.1 0.2 0.3 0.4 0.5 0.6
-2
0
2
x 10
4
Time (seconds)
Vabc1
0 0.1 0.2 0.3 0.4 0.5 0.6
-200
0
200
Time (seconds)
Current(A)
0 0.1 0.2 0.3 0.4 0.5 0.6
-2
0
2
x 10
4
Time (seconds)
Voltage(v)
0 0.1 0.2 0.3 0.4 0.5 0.6
-200
0
200
Time (seconds)
Current(A)
0 0.1 0.2 0.3 0.4 0.5 0.6
-150
-100
-50
0
50
Selected signal: 30 cycles. FFT window (in red): 5 cycles
Time (s)
0 200 400 600 800 1000
0
5
10
15
20
25
Frequency (Hz)
Fundamental (50Hz) = 32.79 , THD= 30.70%
Mag(%ofFundamental)
0 0.1 0.2 0.3 0.4 0.5 0.6
-150
-100
-50
0
50
Selected signal: 30 cycles. FFT window (in red): 5 cycles
Time (s)
0 200 400 600 800 1000
0
1
2
3
Fundamental (50Hz) = 76.06 , THD= 3.94%
Frequency (Hz)
Mag(%ofFundamental)

3. IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163
__________________________________________________________________________________________
Volume: 01 Issue: 03 | Nov-2012, Available @ http://www.ijret.org 457
Time(s)
Sending end Active power
power
Receiving end Active power
Activepower(MW)
Receiving end reactive power
Reactivepower(VA)
Time(s)
Voltage(V)
The Total Harmonic Distortion (THD), which was 30.70%
Fig.4 (a) before compensation was effectively reduced to 3.94
% Fig. 4(b) after compensation using PI controller.
Fig4(c) Distorted Source voltage THD=0.36%
Fig4(d) compensated Source voltage THD=.09%
Fig5 (a) sending and receiving end active power
Fig5 (b) Receiving and sending end reactive power
Fig5(c) Sending and receiving end
Fig 5(d) Power factor
4. PERFORMANCE OF UPQC WITH FUZZY
LOGIC CONTROLLER
In fuzzy logic, the linguistic variables are expressed by fuzzy
sets defined on their respective universes. Error (input) can be
selected as current, voltage or impedance, according to selected
control type. The output of the fuzzy logic controller is the
angle signal and the pulse generator provides firing pulses to
thyristors. The fuzzy control is basically a nonlinear and
adaptive in nature, giving the robust performance in the cases
where in the effects of parameter variation of controller is
present.
Fig 6(a) input 1
0 0.1 0.2 0.3 0.4 0.5 0.6
-1
0
1
x 10
4Selected signal: 30 cycles. FFT window (in red): 5 cycles
Time (s)
0 100 200 300 400 500 600 700 800 900 1000
0
0.05
0.1
0.15
0.2
0.25
Fundamental (50Hz) = 1.555e+004 , THD= 0.36%
Frequency (Hz)
Mag(%ofFundamental)
0 0.1 0.2 0.3 0.4 0.5 0.6
-1
0
1
x 10
4Selected signal: 30 cycles. FFT window (in red): 5 cycles
Time (s)
0 200 400 600 800 1000
0
0.05
0.1
0.15
0.2
Fundamental (50Hz) = 1.56e+004 , THD= 0.09%
Frequency (Hz)
Mag(%ofFundamental)
0 0.1 0.2 0.3 0.4 0.5 0.6
0
1
2
3
x 10
6
0 0.1 0.2 0.3 0.4 0.5 0.6
-1.5
-1
-0.5
0
0.5
1
1.5
2
x 10
6
Sending end
Reactive Power
0 0.1 0.2 0.3 0.4 0.5 0.6
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
x 10
4
0 0.1 0.2 0.3 0.4 0.5 0.6
0.6
0.8
1
Time (seconds)
Powerfactor
Receiving end
Voltage
Sending end Voltage

4. IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163
__________________________________________________________________________________________
Volume: 01 Issue: 03 | Nov-2012, Available @ http://www.ijret.org 458
Fig 6(b) input 2
Fig6(c) output
Fig.7 (a) compensated source current THD using Fuzzy logic
controller = 3.62%
Fig7 (b) source voltage THD using Fuzzy logic controller
=.08%
CONCLUSIONS
The Results obtained from the simulation shows better
performance of UPQC when fuzzy logic controller used then
that of PI controller in terms of harmonic compensation and dc
capacitor voltage balancing at load terminals in switching as
well as unbalanced conditions. Under this condition the
dynamic response of fuzzy logic controller proved to be faster
than PI controller. Hence it is proved that fuzzy logic controller
is superior then PI controller.
Table 1.1 shows simulated performance parameters of PI
controller and fuzzy logic controller.
1. Source current THD:-
As shown in table, before compensation when UPQC not
connected, source current THD is 30.70%, due to non linear RL
load. The dominant harmonic is 5th harmonic and its
magnitude is 29.5% of fundamental component. There is
passive filter LC connected on shunt side which is tuned to 5th
harmonic. Source current THD after compensation when
UPQC connected at 0.1s and PI controller used, source current
THD is reduced to 3.94% and the magnitude of the 5th
harmonic also reduces to 3.81% of fundamental component.
But when PI controller replaced by the fuzzy logic controller,
source current THD reduces to 3.52%. And the magnitude of
the 5th harmonic also reduces to 3.76% of fundamental
component. So in the 1st, 3rd factor of Table 4.1, fuzzy
controller proves to be more a advantageous.
2. Dynamic response
This parameter is the measurement of how quickly controllers
respond to the situation, in table 4.1 dynamic response shows
the time taken by the controller to reduce THD from 30.70% to
3.94%. as shown, time taken by PI controller is 0.20s and time
taken by the fuzzy controller is 0.15s. Hence it is proved that
dynamic response of th PI controller is faster than the fuzzy
logic controller.
0 0.1 0.2 0.3 0.4 0.5 0.6
-150
-100
-50
0
50
Selected signal: 30 cycles. FFT window (in red): 5 cycles
Time (s)
0 100 200 300 400 500 600 700 800 900 1000
0
0.5
1
1.5
2
2.5
3
3.5
Fundamental (50Hz) = 78.54 , THD= 3.65%
Frequency (Hz)
Mag(%ofFundamental)
0 0.1 0.2 0.3 0.4 0.5 0.6
-1
0
1
x 10
4 Selected signal: 30 cycles. FFT window (in red): 5 cycles
Time (s)
0 200 400 600 800 1000
0
0.05
0.1
Frequency (Hz)
Fundamental (50Hz) = 1.56e+004 , THD= 0.08%
Mag(%ofFundamental)
S.no Factor PI Cont
Roller
Fuzzy
Cont
Roller
1 Source current THD 3.94% 3.52%
2 Dynamic response Slow
( 0.20s)
Fast
( 0.10s)
4 Capacitor charging Slower Faster
5 Capacitor voltage
balance under
unbalanced load
condition
Less
stable
More
stable
6 Source current THD
with switching RL load
3.65% 3.59%

5. IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163
__________________________________________________________________________________________
Volume: 01 Issue: 03 | Nov-2012, Available @ http://www.ijret.org 459
3. DC capacitor voltage regulation
The dc link voltage that feeds both the shunt and series
inverters. The capacitor is effectively charged to the reference
voltage, vdc drawing the charging current from the supply.
Once it is charged to required value, it is held constant using PI
and fuzzy controller. There is no drop in the capacitor voltage.
Fig. 2.20 shows the dc link voltage which reflects more the
disturbance in the supply voltage because use of PI controller.
But when fuzzy controller replaced, as shown in Fig. 3.6c, it
shows less fluctuation and hence smoother exchange of real
power between STATCOM and SSSC.
It is clearly evident from the Table 1.1 that in terms of source
current THD, Dynamic response, capacitor charging, Capacitor
voltage balance under unbalance load condition, Source current
THD with switching RL load, fuzzy logic control having an
edge over PI controller.
REFERENCES:-
[1] IEEE standard 519-1992, IEEE recommended practices
and requirement for harmonic control in electrical power
systems, IEEE, Inc. 1993.
[2] L. Gyugi, R. A. Otto, and T. H. Putman, “Principles and
application of static, thyristor controlled shunt
compensators,” IEEE Trans. on Power Apparatus and
Systems, vol. PAS-97, pp. 1935-1945, sept. /oct. 1978
[3] L. Gyugi, “Reactive power generation and control by
thyristor circuit,” IEEE Trans. Industrial Applications,
pp. 1935- 1945, sept/oct 1979.
[4] L. Gyugyi and E. C. Strycula, “Active ac power filters,”
in Proc. 1976 IEEE/IAS Annual Meeting, 1976, pp.
529-535.
[5] L. Gyugi, ”Unified power flow control concept For
flexible ac transmission system, ” IEE proc.-C, vol. 139,
no. 4, July 92, pp 323-332.
[6] H. Akagi, “Performance and modeling of a shunt active
filter for Installation on power distribution systems,” to
be presented at the 1996 IEEE-PES International
Conference on Harmonics and Quality of Power, Oct.
16-18, 1996.