Power Quality Improvement by Unified Power Quality Conditioner

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Hindawi Publishing Corporation
ξ€ e Scientific World Journal
Volume 2014, Article ID 391975, 7 pages
http://dx.doi.org/10.1155/2014/391975
Research Article
Power Quality Improvement by Unified Power Quality
Conditioner Based on CSC Topology Using Synchronous
Reference Frame Theory
Rajasekaran Dharmalingam,1 Subhransu Sekhar Dash,2 Karthikrajan Senthilnathan,3
Arun Bhaskar Mayilvaganan,3 and Subramani Chinnamuthu2
1
Department of Electrical and Electronics Engineering, RMD Engineering College, Chennai, India
Department of Electrical and Electronics Engineering, SRM University, Chennai, India
3
Department of Electrical and Electronics Engineering, Velammal Engineering College, Chennai, India
2
Correspondence should be addressed to Karthikrajan Senthilnathan; karthik.svkk@gmail.com
Received 27 February 2014; Accepted 19 March 2014; Published 11 June 2014
Academic Editors: N. Barsoum, P. Vasant, and G.-W. Weber
Copyright © 2014 Rajasekaran Dharmalingam et al. This is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
This paper deals with the performance of unified power quality conditioner (UPQC) based on current source converter (CSC)
topology. UPQC is used to mitigate the power quality problems like harmonics and sag. The shunt and series active filter performs
the simultaneous elimination of current and voltage problems. The power fed is linked through common DC link and maintains
constant real power exchange. The DC link is connected through the reactor. The real power supply is given by the photovoltaic
system for the compensation of power quality problems. The reference current and voltage generation for shunt and series converter
is based on phase locked loop and synchronous reference frame theory. The proposed UPQC-CSC design has superior performance
for mitigating the power quality problems.
1. Introduction
The main impact in the power distribution system is the
quality of power, which causes more distortion in the source
due to using nonlinear loads (power electronics loads).
The main cause for distortion is harmonics, notching, and
interharmonics. Distortion is that the fundamental frequency
sine wave is represented as super position of all harmonic
frequency sine waves on fundamental sine wave. The usage
of power electronics loads is increased day by day, while
considering that industries power electronics drives are used
for the automation of the industries. To compensate the
distortion in the system, passive filters were used and while
using the passive filters particular harmonic range is only
eliminated. In order to overcome the drawbacks of passive
filter, for the elimination of power quality problems, active
filters were used.
Power quality problems are harmonics, sag, and swell
which are mitigated by the active filters by the configuration
of dynamic voltage restorer (DVR), distribution-static synchronous compensator (D-STATCOM), and unified power
quality conditioner (UPQC) [1]. In this paper UPQC [2] is
used for the mitigation of the power quality problems which
is the combination of series and shunt active filters. The series
and shunt active power filters are voltage and current source
converters which are controlled by the PWM signals which
are generated by the controllers.
2. Unified Power Quality Conditioner (UPQC)
The unified power quality conditioner is commonly called
UPQC. The design configuration is based on the connection
of series and shunt inverters. In this, the design configuration
2
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Vload
A
Iload
Line parameters
AC voltage source
Isource
+
−
R
L
1
+
Nonlinear load
Series
transformer
Gate
pulse
2
Vsource
Pulse
DC link
g
A
+
−
Vdc
Shunt
active power filter
+
g
−
A
Series
active power filter
Figure 1: The design configuration of UPQC-CSC.
is right series and left shunt with the current source converter
(CSC) [3, 4]. In this paper, UPQC-CSC [5, 6] is designed and
analysis of the results has been done. Unified power quality
conditioner (UPQC) for nonlinear and voltage sensitive load
has following facilities.
(i) It reduces the harmonics in the supply current, so that
it can improve utility current quality for nonlinear
loads.
(ii) UPQC provides the VAR requirement of the load,
so that the supply voltage and current are always in
phase; therefore, no additional power factor correction equipment is required.
(iii) UPQC maintains load end voltage at the rated value
even in the presence of supply voltage sag.
The design configuration of UPQC-CSC [7] is shown in
Figure 1.
3. Synchronous Reference Frame (SRF) Theory
The control strategy for the unified power quality conditioner
is based on the synchronous reference frame (SRF) [8, 9]
theory. In this theory controlling of the three-phase converters using the rotating frame theory by converting the source
voltage and current to direct and quadrature axis is done. The
voltage is converted to π‘‘π‘ž in the series controller and current
is converted to π‘‘π‘ž in the series controller. Consider
π‘‰π‘Ž
[ 𝑉𝑏 ]
[𝑉𝐢]
1
1
1
[ √2
]
√2
√2
[
] 𝑉𝑑
2πœ‹
2πœ‹
[
2 sin (wt) sin (wt −
) sin (wt +
)]
][ ]
=√ [
3
3 ] π‘‰π‘ž .
3[
[
] 𝑉
2πœ‹
2πœ‹
[cos (wt) cos (wt −
) cos (wt +
)] [ 0 ]
3
3
[
]
(1)
σΈ€ 
in order to
The π‘‘π‘ž transform is again converted to the π‘‰π‘Žπ‘π‘
get the reference signal which is used for the generation of the
pulse for the three-phase converter in the system. Consider
1
sin (wt)
cos (wt)
[ √2
]
[ 1
]
σΈ€ 
2πœ‹
2πœ‹
[
]
𝑉𝑑
sin (wt −
) cos (wt −
)] π‘‰π‘ŽσΈ€ 
[
2
[π‘‰π‘ž ] = √ [ √2
3
3 ] [ 𝑉𝑏 ].
]
3[
σΈ€ 
[
]
[𝑉0 ]
2πœ‹
2πœ‹ ] [𝑉𝐢]
[ 1
[
sin (wt +
) cos (wt +
)]
√2
3
3
[
]
(2)
The shunt converter performs the process of elimination of
harmonics and series converter performs process of elimination of the voltage related problems. The control block
diagram for the synchronous reference frame theory is shown
in Figure 2.
3.1. Series Controller. The control strategy of the series controller is achieved through the synchronous reference frame
theory. In this, the series controller gets the reference signal
for the generation of pulse for the three-phase converter, by
comparing the source voltage with distortion and constant
voltage. The source voltage 𝑉𝑠 π‘Žπ‘π‘ and constant voltage 𝑉ref π‘Žπ‘π‘
are converted to the 𝑉𝑠 π‘‘π‘ž0 and 𝑉ref π‘‘π‘ž0 transform. The 𝑉𝑠 π‘‘π‘ž0
and 𝑉ref π‘‘π‘ž0 are compared to get the error signal which is
σΈ€ 
σΈ€ 
. The π‘‰π‘™π‘Žπ‘π‘
is the reference signal for
again converted to π‘‰π‘™π‘Žπ‘π‘
the pulse generator. The simulation diagram for synchronous
reference frame theory based series controller is shown in
Figure 3.
3.2. Shunt Controller. The shunt converter has the function of
compensating the current related problems. Along with the
shunt controller, DC link voltage is maintained. The π‘Žπ‘π‘ to
π‘‘π‘ž0 transform is inversed and converted to π‘Žπ‘π‘; that signal is
given as the reference signal and the measured signal is given
to the hysteresis band PWM to produce the pulse signals for
the operation of shunt converter. The simulation diagram for
shunt controller is shown in Figure 4.
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3
isb
isd
T
LPF
+
isd
E
isq
isc
σ³°€
is0
σ³°€
is0
=0
is0
isa
+
σ³°€
isd
σ³°€
isq
=0
σ³°€
isd
T−1
σ³°€
isq
Shunt
APF
Hysteresis
band
PWM
σ³°€
VDC
VDC
E
PI
I
dloss
wt
G1
G2
G3
G4
G5
G6
isa isb isc
wt
PLL
wt
Vsa
Vsb
+
Vsd
T
Vsq
Vsc
Vlaσ³°€
Vs0
Vs0
Vsd
E
Vsq
−
Vlbσ³°€
T−1
Vlcσ³°€
Series
APF
G1
G2
Hysteresis
band
G3
G4
PWM
G5
G6
wt
Vref
A
Vref
B
Vref 0
Vref d
T
T −1
VIaVIb VIc
Vref q
T−1
Vref C
Figure 2: Control block diagram.
−+
1
A
2
B
3
C
4
Vs
1
A∗
2
B∗
3
C∗
dq0
abc
abc
dq0
−+
Sin cos
Sin cos
Vabc(pu) Si Co
Id, Iq
3-phase PLL1
PLL
A Vabc
I
B abc
a
C
C cb
Three-phase
Three-phase
programmable V-I measurement
voltage source
N
A
+ B
abc
dq0
Vabc(pu) Si Co
Sin cos
3-phase PLL2
Figure 3: Simulation of synchronous reference frame theory based series controller.
4
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F0 = 50 Hz
Freq
Sin cos Terminator
1
A
2
B
3
C
++
abc
Sin cos
abc
dq0
Sin cos
1
A∗
2
B∗
3
C∗
dq0
F0 = 50 Hz
wt
PLL Terminator 1
Id, Iq
4
Vdc
Figure 4: Simulation of shunt controller.
+
1
+V
Voltage measurement
−+
Scope 9
730
2
−
PI
Vdc
Discrete
PI controller 1
Goto3
Conn2 Conn1
Constant 1
Solar
Figure 5: DC link controller.
3.3. DC Link Controller. The direct current link controller
has the PI controller in which the constant voltage is given
as the set point and the measured voltage is given for the
comparison to maintain the constant voltage. The PV array
is attached with the DC link for injection. The DC link
controller is shown in Figure 5.
4. Simulation and Results
The UPQC-CSC has the reactor as the DC link for the series
and shunt converter and is controlled by the synchronous
reference frame (SRF) theory and the pulse is generated by
the hysteresis band controller. The shunt and series converters
have the function of compensating current and voltage problems, respectively. The simulation of UPQC-CSC is shown
in Figure 6. The output of UPQC-CSC is shown in Figure 7
which shows the voltage with sag, current with harmonics,
and compensated voltage and current. The compensation of
sag is shown in Figure 8. The shunt compensation is shown
in Figure 9. The series compensation is shown in Figure 10.
4.1. System Parameters. Consider
source voltage: 415 V, 50 Hz;
load parameters:
resistive load: 10 KΩ;
inductive load: 2 mH;
RLC load: 10 KW;
shunt inverter side:
LC filter: 3.5 mH, 5 Ω, and 10 πœ‡F;
series inverter side:
LC filter: 12 πœ‡H, 5 Ω, and 10 πœ‡F;
DC link reactor:
for UPQC-CSC: 200 mH;
solar voltage: 727.1 V.
Figure 7 shows the simulation output of the UPQC-CSC
simulation for voltage sag mitigation. The sudden addition of
load in the system causes voltage sag for the time duration of
0.04 to 0.08 s. The compensation for the sag is by the series
active filter using the SRF theory for the reference signal
generated and pulse generated by the hysteresis band and
given to the IGBTs in the filter.
The compensation of the voltage related problems is done
by the series active filter to maintain the system voltage 1
5
−
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Vs
A
B
C
A
B
C
Three-phase
series RLC branch
A
B
A
A1+
A1
B1+
B1
C1+
C1
A
B
C
C
Nonlinear load
B
B2+
B2
B1
C2+
C2
A2+
A2
Discrete,
Ts = 5e − 006 s
A1
C
Sag generator
Powergui
B1
C1
Shunt filter
Vm888
A1
Three-phase
V-I measurement 2
g
B
C
A
Series_controller
g
Shunt-controller
C1
−
+
DC controller
C
Series inverter
g
+
A
g
+
A
B
B
A
Filter
B
−
−
C
C
Figure 6: UPQC-CSC simulation diagram.
P.U. By using the SRF theory even a minor disturbance in
the system is sensed and compensation is done; Figure 10
shows the series compensation for the system. The harmonics
compensation is done by the shunt active filter along with the
DC link voltage controller. Total harmonics distortion (THD)
for the current source converter is shown in Table 1. Figure 9
shows the compensation given for reducing the harmonics.
The Fourier fast transform analysis graph for the source
voltage THD of about 0.89% is shown in Figure 11.
The Fourier fast transform analysis graph for the load
voltage with the nonlinear loading conditions of about 0.45%
is shown in Figure 12.
The Fourier fast transform analysis graph for the load
current with the nonlinear loading conditions of about 0.17%
is shown in Figure 13.
5. Conclusion
In this paper, synchronous reference frame theory based
control method is implemented to control the working of
unified power quality conditioner based on current source
Table 1: Total harmonics distortion (THD in %).
Hn order
H
H3
H5
H7
H9
H11
THD
Current source converter
Load
Source
voltage
voltage
(𝑉𝐿 ) in %
(𝑉𝑠 ) in %
0.97
0.28
0.09
0.03
0.03
0.02
0.89
0.99
0.08
0.05
0.06
0.04
0.03
0.45
Load
current
(𝐼𝐿 ) in %
0.04
0.08
0.06
0.02
0.04
0.06
0.17
converter topology. The simulation results show that the
device is capable of compensating the current harmonics
under unbalanced and nonlinear load conditions, simultaneously mitigating voltage sag and swell. The proposed
UPQC-CSC design has superior performance for mitigating
6
The Scientific World Journal
Series compensation-mitigation of sag
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Time (s)
Current at PCC before compensation
0.1
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Time (s)
Voltage at load after compensation
0.1
1.5
0.5
−0.5
−1.5
Voltage P.U.
10
0
−10
Sag at PCC
0
0
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.1
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Time (s)
0.1
Voltage P.U.
Voltage P.U.
Voltage before compensation
1.5
0.5
−0.5
−1.5
0.2
0
−0.2
−0.4
1.5
0.5
−0.5
−1.5
Figure 10: Series injection for sag compensation.
FFT analysis
Fundamental (50 Hz) = 0.9758, THD = 0.89%
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Time (s)
Compensating voltage
Figure 11: Source voltage THD graph.
0.1
FFT analysis
Fundamental (50 Hz)=0.9998, THD = 0.45%
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.1
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
0.1
Time (s)
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
0
Figure 8: PCC voltage with sag, compensating voltage and voltage
after compensation.
100 200 300 400 500 600 700 800 900 1000
Frequency (Hz)
Figure 12: Load voltage THD graph.
Shunt compensation
FFT analysis
Fundamental (50 Hz) = 17.57, THD = 0.17%
Mag (% of fundamental)
Current (A)
100 200 300 400 500 600 700 800 900 1000
Frequency (Hz)
Time (s)
Voltage after compensation
25
20
15
10
5
0
−5
−10
−15
−20
−25
0.1
Time (s)
Current at load
Mag (% of fundamental)
20
0
−20
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Figure 7: Output of source voltage and current and load voltage and
current waveform.
Voltage P.U.
0.25
0.2
0.15
0.1
0.05
0
−0.05
−0.1
−0.15
−0.2
−0.25
Time (s)
Mag (% of fundamental)
Iload (A)
VI P.U.
Is (A)
Vs P.U.
Voltage at PCC before compensation
1.5
0.5
−0.5
−1.5
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09
Time (s)
Figure 9: Shunt injection for THD compensation.
0.1
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
0
100 200 300 400 500 600 700 800 900 1000
Frequency (Hz)
Figure 13: Load current THD graph.
The Scientific World Journal
the power quality problems. The series converter is capable of
mitigating the voltage related problems and shunt converter
is capable of mitigating the harmonics.
Conflict of Interests
The authors declare that there is no conflict of interests
regarding the publication of this paper.
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