Advance in Electronic and Electric Engineering.
ISSN 2231-1297, Volume 4, Number 2 (2014), pp. 121-126
© Research India Publications
http://www.ripublication.com/aeee.htm
Harmonic Mitigation Using Unified Power Quality
Conditioners and Hybrid Active Power Filters
M. Sharanya1, Dr. B. Basavaraja2 and Dr. M. Sasikala3
1
Associate Professor, Department of EEE, V.B.I.T, Ghatkesar, Hyderabad, India.
2
HOD, Vice Principal, GITAM University, Hyderabad Campus, India.
3
Professor, Department of EEE, CVR College of Engineering, Hyderabad, India.
E-mail: 1sharanya2702@gmail.com 2banakara36@gmail.com
3
sasi_mun@rediffmail.com
1
www.vbithyd.ac.in 2 www.gitam.edu 3 www.cvr.ac.in
Abstract
The power quality issues are of great concern now a days. The
increasing use of power electronic devices based nonlinear loads
deteriorate the quality of power. Power electronic appliances are
widely used in industrial, commercial and utility system thus leading to
various power quality problems. This leads to harmonics being injected
into the distribution system and also reactive power burden. Power
electronic devices based custom power devices can be used to mitigate
these power quality problems. Some of these custom power devices are
DSTATCOM, Dynamic voltage restorer(DVR), unified power quality
conditioners(UPQC), and filters. In this paper the power quality
improvement is done by mitigating harmonics using the custom power
devices like UPQC and Hybrid active power filters(HAPF). UPQC
consists of combination of series and shunt active filters. Series filter
inject voltage which gets added at the point of common coupling and
hence the voltage at the load end gets unchanged with the voltage
disturbances. Shunt active filter compensates the load reactive power
demand and hence mitigates the harmonics from supply current and
also maintains the DC link voltage. The other custom power device
discussed in this paper is hybrid active power filter. Hybrid active
power filter is the combination of passive and active filters. Passive
filters are LC tuned filters used for the harmonic mitigation but are
bulky and has compensation problem. Active filters are effective in
harmonic mitigation but its cost increases with higher ratings. Hence
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hybrid active filter provides cost effective harmonic mitigation
solution. The active filters are designed using IGBT based switches
and are controlled by using PI controllers. Simulation is done using
MATLAB/SIMULINK environment and the results show that both
these custom power devices, UPQC and HAPF reduces the harmonics.
The total harmonic distortion (THD) values by this control method is
reduced to less than 5% as per IEEE standards. The proposed controls
scheme provides better steady state and dynamic responses.
Keywords: Power quality; custom power device; DSTATCOM; DVR;
UPQC; HAPF; MATLAB/SIMULINK; THD.
1. Introduction
In distribution power systems the power quality problems are not new, but the
awareness of customer to these problems has increased recently. The quality of power
at the point of commoncoupling (PCC) with the utility grid is governed by the various
standards and the IEEE-519 standard is widely accepted. Flexible solutions to these
power quality problems are obtained by using power electronic converters that is by
using custom power devices. (Nikita Hari et al, 2011)
Various power quality problems like: sag, swell, voltage imbalance, flickers
harmonics and reactive currents can be compensated by using UPQC. UPQC is a
combination of shunt and series active filters connected through a common dc link
capacitor. The series active filter injects voltage, which gets added at the PCC and the
main objectives of shunt active filter are: to compensate for the load reactive power
demand and unbalance, to eliminate the harmonics from the supply current, and to
regulate the common dc link voltage. (Nikita Hari et al, 2011)
Another custom power device used for the power quality improvement is Hybrid
active power filters. Conventional passive filters compensate reactive power along
with harmonics and are of low cost and have simple structure. But these have the
problem of tuning, resonance and are bulky. To overcome these problems active filters
are used which are best suited for the compensation under dynamic load conditions.
The main drawback of these filters is that it’s cost increases with the increase in the
ratings. Hence hybrid active power filters are used which is the combination of both
passive and active filters and has the advantages of both these filters. (P. Thirumoorthy
et al, 2012; M. Salehifar et al, 2010)
2. Unified Power Quality Conditioner
The UPQC is a custom power device that has shunt and series active filters, connected
back to back on dc side and sharing a common DC capacitor as shown in Fig 1. It has
two voltage source inverters (VSIs) that are connected to a common DC energy storage
capacitor. One of these two VSIs is connected in series with the feeder and the other is
connected in parallel to the same feeder. (Nikita Hari et al, 2011)
Harmonic Mitigation Using Unified Power Quality Conditioners and Hybrid
123
Fig. 1: Model of UPQC.
2.1 Control of UPQC
The UPQC system controller consists of series APF and shunt APF controller. APF
controller generates the reference current signal measuring the load voltage, load
current, injected current and capacitor voltage. APF controller protects the overall
system by closing the firing pulses going to IGBT drivers. Shunt APF also regulates
the DC link voltage. Hysteresis control technique is used to generate the gate
switching pulses of APF. Series APF controller generates the reference voltage and
sag detection signals measuring the supply voltages. Series APF controller is based
PLL. The reference voltage signal and fault detection signal are extracted
simultaneously. Series APF controller uses independent fault detection method for
each phase and thus each H-bridge inverter is controlled independently. Sinusoidal
PWM control technique is used to generate the gate switching pulses of Series APF.
500
0
-500
0
Load current
Source voltage
2.2 Simulation results of UPQC
Fig 2 and fig 3 shows the simulation results for the case where the system is in steady
state. Due to power electronic load the current waveform is distorted and is
unbalanced. Voltage waveform is also distorted.
2000
4000
6000
Time(sec)
Fig2:
2 Source
Sourcevoltage
voltage
without
UPQC
Fig.
without
UPQC.
50
0
-50
0
Fig.
2000
4000
6000
Time(sec)
3 Load
current
withoutUPQC.
UPQC
3:FigLoad
current
without
8000
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M. Sharanya et al
Fig. 4 and Fig 5 shows the results after UPQC is connected to the system. The
waveforms are balanced and THD is greatly reduced from 80.3% to 2.73% .This
shows that UPQC compensates harmonics to a great extent.
SourcevoltageandLoadcurrent
500
0
-500
0
1000
2000
3000
Time(sec)
4000
5000
6000
Fig. 4: Source voltage and load current with UPQC.
3. Hybrid Active Power Filters
Hybrid active power filters is also a custom power device used for harmonic
mitigation. HAPF is the combination of passive and active filters which can be either
connected in series or shunt. The passive filters are LC tuned filters and active filters
are voltage source converters. The combination of these two can reduce the harmonics
and also compensate the reactive power.
3.1 Control of HAPF
Fig 5 shows the configuration of HAPF. The proposed HAPF has series active filter
and two parallel single tuned passive filters in series with the active filter. Two passive
filters are tuned in dominants harmonic frequencies of 3rd and 5th. HSAF is
considered with a nonlinear load to show the effectiveness of the proposed method in
harmonic elimination and reactive power compensation.
Fig. 5: HAPF system configuration.
Harmonic Mitigation Using Unified Power Quality Conditioners and Hybrid
125
L o a d c u rre n t
S ourc e c urren t
3.2 Simulation results of HAPF
Simulation is carried out by considering only passive filter and then by considering
both passive and active filter. Without filter connected to the system the load current is
distorted and the current drawn from the supply. And the THD value is 82.65%. With
only passive filter connected the waveforms are improved to some extent and the THD
value is reduced to 4.9%. By connecting HAPF the current drawn from the supply
becomes purely sinusoidal and the THD value is further reduced to 1.02%. Fig 7 and 8
gives the source current and load current when HAPF is connected.
20
0
-20
0.6
0.8
1
1.2
1.4
4
Time(sec)
x 10
Fig 7 Source
current
withHAPF.
HAPF
Fig. 7: Source
current
with
20
0
-20
2000
3000
4000
5000
6000
Time (sec)
8 Load
current with
with HAPF
Fig. 8:Fig
Load
current
HAPF.
Fig. 9 & Fig. 10: Spectrum analysis with UPQC 2.73% and with HAPF 1.02%
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M. Sharanya et al
Table 1: Comparision of THD values of UPQC and HAPF.
UPQC
Without With
UPQC UPQC
2.73%
% THD Value 80.3%
Without filter
82.65%
HAPF
With Passive
filter only
4.9%
With
HAPF
1.02%
4. Conclusions
The work in this paper is to develop control schemes of UPQC for power quality
improvement so that the performance of UPQC is enhanced. The steady state and
dynamic response of UPQC is enhanced due to its control method using DC voltage
regulation, hysteresis controller for shunt active filter and PWM controller for series
active filter. Simulation results shows that by using this control scheme the harmonic
reduction is good, the source voltage and load current are compensated and also the
DC voltage is well regulated. The main objective of this work is also to develop a cost
effective HAPF for harmonic mitigation and reactive power compensation with a
control method to control the shunt active power filter. This method employs a cost
effective solution for the high power applications. The effectiveness of this method is
proved with simulation results.
References
[1]
[2]
[3]
[4]
[5]
K Triveni Krishna and E Aswani Kumar(2012), Article in a journal, Intl. J. of
engg. And science research, 2, 11, pp. 1696-1705.
M. Salehifar, H A Mohammad pour, A H Moghadasi and A Shoulaie(2010),
Article in IEEE Intl. conference on power electronics and drives and
technologies.
Nikita Hari, K Vijay kumar and D Subranshu Shekar(2011), Article in IEEE
proceedings of ICETECT.
P Thirumoorthy and N Yadaiah (2012) Article in ACEEE Int. J. on Electrical
and Power Engineering, 3,1, PP. 62-68.
Y Ching Wang and T Lin Lee (2012) Article in IEEE International
Symposium on Power Electronics for Distributed Generation Systems (PEDG)
2012.