Download III. power factor correction

International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Design and Simulation of Active Harmonic
Filter for Reducing Harmonic distortion and
Improving Power Factor in Industrial Load
Saw Sandar Moe,

Abstract—Power factor correction in industrial facilities has
become a problem nowadays because of the widespread use of
power electronic equipment. This paper presents a method
capable of designing and simulation of active power filters to
reduce harmonic distortion and correct the power factor. The
modern electric power systems that include non-linear loads
may experience power quality problem such as harmonic
distortion and reducing power factor. Non-linear loads draw
current that passes through all of the impedances between the
loads and the system sources. The current causes power quality
problems. This paper also investigates the use of harmonic
elimination methods to evaluate and reduce total harmonic
distortion (THD) and power factor correction in the three-phase
system. The proposed method improve power factor and reduce
the total harmonic distortion within an acceptable range.
Index Terms— Active power filter, Power factor correction,
Nonlinear loads, Harmonic, Total harmonic distortion.
I. INTRODUCTION
Nowadays, the development of the industries is
become a main roll during the transition period of
agriculture-based country to industry-based country. In
industrial sector improving, these points are major
parameters to be fulfilled. In this paper, SAF is used to obtain
electric power continuously and to achieve the electric power
in high quality.
Harmonic distortion is a major problem in
power system and reduction of harmonic is very essential for
the power quality improvement. Since most loads in modern
industrial power supply system are non linear loads with the
development of power electronics, the converters are widely
used in the power supply devices and control application.
Harmonic currents produced by nonlinear loads are injected
back into power distribution systems through the point of
common coupling (PCC).As the harmonic currents pass
through the line impedance of the system, harmonic voltage
appear, causing distortion at the PCC.
Different topologies and control techniques have been
proposed for their implementation. AFs are superior to
passive filters in terms of filtering characteristics and improve
the system stability by removing resonance related problems
[1]. Harmonics in power distribution system are current or
voltage that are integer multiples of fundamental frequency.
Ideally, voltage and current waveforms are perfect sinusoids.
Saw Sandar Moe, Electrical Power Engineering, Mandalay
Technological University, ([email protected]). Mandalay,
Myanmar, +9509444012497.
However, because of the increased popularity of electronic
and non linear loads, these waveforms become distorted. In
order to quantify the distortion, the term of Total Harmonics
Distortion (THD) is used [2]. Voltage and current harmonic
produced by nonlinear loads increase power losses and,
therefore, have a negative impact on electric utility
distribution system components. While the exact relationship
between harmonics and losses is very complex and difficult to
generalize, the well-established concept of power factor does
provide some measure of the relationship, and it is useful
when comparing the relative impacts of nonlinear
loads–providing that harmonics are incorporated into the
power factor definition. The major objectives in this paper are
to use shunt active filter for following - (i) to improve the
power factor, (ii) to reduce total harmonic distortion within
standard limits [3].
II. ACTIVE HARMONIC FILTER
The active power filter (APF) is a device that is connected in
system to cancels the reactive and harmonic currents from a
group of nonlinear loads so that the resulting total current
drawn from the ac main is sinusoidal. The basic principle of
APF is to utilize power electronics technologies to produce
specific currents components that cancel the harmonic
currents components caused by the nonlinear load. APF’s
have a number of advantages over the passive filters. APF can
suppress not only the supply current harmonics, but also the
reactive currents. Active filters can offer a flexible and
versatile solution to voltage quality problems and operates in
a wide frequency range, adjusting their operation to the
resultant harmonic spectrum. Active filters can be classified
according to the ways:
Active Power Filter
Shunt APF
Current
source
inveter
Voltage
source
inveter
Series APF
Hybird APF
Shunt APF
Series APF
Shunt APF
+
+
+
Series APF
Shunt PF
Shunt PF
APF in
series
with
shunt PF
Fig.1 Classification of Active Power Filter
A. Shunt active power filter
The shunt active power filter has proved to be a
useful device to eliminate harmonic currents and to
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
compensate reactive power for linear/nonlinear loads. A
three-phase system feeding an inverter load has been selected
to study the performance of the APF system. It has been
observed that due to the non-linear characteristics of power
electronics loads the THD’s of source current and terminal
voltage fall well below the IEEE-519 standard and in
principle APF system is used to inject a current equal in
magnitude but in phase opposition to harmonic current to
achieve a purely sinusoidal current wave in phase with the
supply voltage.Figure.2.shows the basic compensation
principle of a shunt active power filter. It is controlled to draw
/ supply a compensating current i from / to the utility, so that
c
it cancels current harmonics on the AC side, and makes the
source current in phase with the source voltage. Figure.3.
shows the different waveforms. Curve A is the load current
waveform and curve B is the desired mains current. Curve C
shows the compensating current injected by the active filter
containing all the harmonics, to make mains current
sinusoidal.
Mains
is
iL
ic
Non Linear Load
L
C
VSI
Fig.2 Shunt active powers filter Basic compensation
principle.
transformer. The injected harmonic voltages are added /
subtracted, to/from the source voltage to maintain a pure
sinusoidal voltage waveform across the nonlinear load.
Mains
is
Vf
iL
Non Linear Load
+
-
Cf
VSI
Fig.4 Principal Configuration of a VSI based series APF.
C. Hybrid Active Power Filter
The combination of shunt active and passive filters has
already been applied to harmonic compensation of large steel
mill drives. The shunt passive filter will draw a large source
current from a stiff system and may act as a sink to the
upstream harmonics. It is required that in a hybrid
combination the filters share compensation properly in the
frequency domain. Depending on application type, series or
parallel configurations or combination of active and passive
filters are used. Active power filters can be used in
conjunction with passive filters improving compensation
characteristics of the passive filter and to avoid the possible
occurrence of the generation of series or parallel resonance.
This type of configuration is very convenient for
compensation of high power medium voltage non-linear
loads, such as large power ac drives with cycloconverters or
high power medium voltage rectifiers for application in arc
furnaces.
III. POWER FACTOR CORRECTION
A. Power Factor
Fig.3 Shunt active power filter-Shapes of load, source and
desired filter current wave forms.
B. Series active power filter
A voltage Vf is injected in series with the line and it
compensates the voltage distortion produced by a nonlinear
load. A series active filter is more suitable for harmonic
compensation of diode rectifiers where the dc voltage for the
inverter is derived from a capacitor, which opposes the
change of the voltage. Figure.4 shows the operation principle
of series APF is based on isolation of the harmonics in
between the nonlinear load and the source. This is obtained by
the injection of harmonic voltages (vf ) across the interfacing
In most modern electrical distribution systems, the
predominant loads are resistive and inductive. Resistive loads
are incandescent lighting and resistance heating. Inductive
loads are AC Motors, induction furnaces, transformers and
ballast-type lighting. Inductive loads require two kinds of
power: (i) active (or) working power to perform the work
(motion) and (ii) reactive power to create and maintain
electro-magnetic fields. The vector sum of the active power
and reactive power make up the total (or) apparent power
used. This is the power generated by the utility for the user to
perform a given amount of work.
Power factor is the ratio of working power to apparent
power. It measures how effectively electrical power is being
used. A high power factor signals efficient utilization of
electrical power, while a low power factor indicates poor
utilization of electrical power. To determine power factor
(PF), divide working power (kW) by apparent power (kVA).
For sinusoidal situations, unity power factor corresponds to
zero reactive power Q, and low power factors correspond to
high Q. Since most loads consume reactive power, low power
factors in sinusoidal systems can be corrected by simply
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
adding shunt capacitors. In a linear or sinusoidal system, the
result is also referred to as the consine;
kW
(1)
PF 
 cosθ
kVA
Total Power Factor, PFt  cos[tan 1
Qt
]
Pt
(3)
k 1

(4)
k 1
Whose rms values can be shown to be


2
Vk


k 1 2
Vrms 
V
2
(5)
krms
k 1
V1rms I1rms

1
1  (THD I /100) 2
 PFdisplacement  PFdistortion
(11)
IV. MODELING OF PROPOSED INDUSTRIAL LOAD

i(t)   Vk sin (kω0 t  θ k )
Pavg1
(2)
B. Power Factor in Nonsinusoidal Situation
Now, consider nonsinusoidal situations, where network
voltages and currents contain harmonics. While some
harmonics are caused by system nonlinearities such as
transformer saturation, most harmonics are produced by
power electronic loads such as adjustable-speed drives and
diode bridge rectifiers. The significant harmonics (above the
fundamental, i.e., the first harmonic) are usually the 3rd, 5th,
and 7th multiples of 50/60 Hz, so that the frequencies of
interest in harmonics studies are in the low-audible range.
When steady-state harmonics are present, voltages and
currents may be represented by Fourier series of the form
v(t)   Vk sin (kω0 t  δ k )
PFtotal 
There are several sources in the industrial loads.
These are loads with nonlinear characteristics. The converters
pulse width modulation converters, cycloconverter, arc
furnace, static var compensators and switch mode power
supplies are typical nonlinear loads producing harmonics.
The electric power is taken from 11 kV feeders in small
industries and 33 kV feeders in large industries. The power
transformers are located at each industry and 400 V three
phase lines execute power distribution in industry. From the
field study, three types of loads are found as follow:
i. Normal AC Loads (induction motors, compressors,
pumps, etc.)
ii. AC Loads with Power Electronic Drives and DC
Loads (DC motors, Speed and Torque Controlled
AC Motors)
iii. Dynamic Loads (Stamping, Metal Pressing, Cutting,
etc)
In the mentioned loads, the first type of loads cause the
displacement power factor and their contribution in current
waveform distortion is small. But the second and third types
are the sources of harmonics due to the power electronic
switches used in their drives and converters.
33 kV Bus bar

2
Ik

k 1 2

I rms 

I
k 1
2
(6)
krms
33/11 kV
Transformer
PCC
15MVA
The average power is given by
Pavg   Vkrms I krms cos(δ k  θ k )  P1avg  P2avg  P3avg  ... (7)
Feeder-1
A frequently used measure of harmonic levels is total
harmonic distortion (or distortion factor), which is the ratio of
the rms value of the harmonics (above fundamental) to the
rms value of the fundamental, times 100%, or
THD V 
V
k 2
krms
PFtotal 
 100% 
V1rms

THD I 

2
 I krms
I1rms
Pavg
V1rms I1rms
V1
 100% 

 Ik
k 2
I1
1.5 ton
Induction
Furnace
1.0 ton
Induction
Furnace
750kVA
Linear
loads
DC
Motor
Feeder-4
11/0.4 kV
Transformer
11/0.4 kV
Transformer
500kVA
500kVA
Linear
loads
0.75 ton
Induction
Furnace
Linear
loads
0.75 ton
Induction
Furnace
k
k 2

2
k 2
V
11/0.4 kV
Transformer
3000kVA
Linear
loads
2
Feeder-3
Feeder-2
11/0.4 kV
Transformer
k 1

11 kV Bus bar
11 kV Bus bar

 100%
(8)
Fig.5 Complete Model of Proposed System
2
 100%
(9)
1
1  (THD V /100)
2
1  (THD I /100) 2
(10)
Neglecting the power contributed by harmonics and also
voltage distortion, as it is generally small. The power factor is
the product of displacement power factor (which is the same
as the fundamental power factor) and is multiplied by the
distortion factor as defined below.
A typical industrial load, induction furnace is taken based
on field study. In this proposed system there are four feeders.
Each feeder has power transformer to supply the factory such
as 3000 kVA, 750 kVA, and two no. of 500kVA respectively.
The power is taken from 11/0.4 kV two winding transformers.
The single line diagram of typical industrial load is illustrated
in figure 5. This factory mainly consists of induction furnaces,
induction machines and DC machine.
Modern induction furnaces use electronic power converters
to supply a variable frequency to the furnace induction coil.
Induction furnaces have been widely used to heat ferrous and
non-ferrous stocks in the forging and extruding industry. The
significant source of harmonic distorting commonly comes
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
from rapidly changing load current such as in induction
furnaces and cycloconverters.
Induction machines are widely used for many purposes for
this factory. It was used to pour the melting iron (or) to rotate
the furnace tank, to cool the existing water from the furnaces
(for cooling system) and to push iron sticks to the furnace, and
to curry the iron sticks.
In this proposed system, DC machine is used to extrude the
iron sticks for getting necessary shape (or) size because it
offers a wider speed range and higher starting torque.
TABLE I
COMPARISON OF THD IN PROPOSED SYSTEM
Parameter
Calculated
Values
Allowable
Values
Remarks
PCC
33.044%
8.0%
Not acceptable
Feeder-1
34.165%
5.0%
Not acceptable
Feeder-2
20.395%
8.0%
Not acceptable
Feeder-3
34.647%
5.0%
Not acceptable
Feeder-4
34.67%
5.0%
Not acceptable
In the above table the percentage of THDs in the proposed
system are not exist within acceptable level. In this paper
Shunt Active Filter (SAF) is used to reduce THD and improve
system’s power factor.
Total Power Factor  PFdisplacement  PFdistortion = 0.83  0.946
= 0.785
This power factor is the condition of without shunt active
filter (SAF).
C. For Feeder-2
DC machine and other nonlinear loads are consisting of in
feeder-2. This feeder is supplied by 750 kVA transformer and
0.4 kV supply.
Q
PFfundamental  cos[tan 1 t ]  0.997
Pt
Distortion Power Factor, PFdistortion 
1
1  (THD I /100) 2
 0.98
Total Power Factor  PFdisplacement  PFdistortion = 0.997  0.98
= 0.977
This power factor is also the condition of without shunt
active filter (SAF).
D. For Feeder-2
In the proposed system, Feeder - 3 and Feeder - 4 have same
parameters such as 500 kVA transformer and 400V supply are
used. Therefore the results are also same.
PFfundamental  cos[tan 1
Distortion Power Factor, PFdistortion 
Qt
]  0.83
Pt
1
1  (THD I /100) 2
 0.945
V. CALCULATION OF POWER FACTOR IN PROPOSED SYSTEM
Total Power Factor  PFdisplacement  PFdistortion = 0.83  0.945
A. For PCC
In the proposed system the Point of Common Coupling
(PCC) was installed outgoing of 15 MVA transformer or
incoming of the whole factory. Therefore, the real power (Pt)
and reactive power (Qt) are the combination of feeder-1,
feeder-2, feeder-3 and feeder-4.The total power factor or
fundamental power factor or displacement power factor;
Q
PFfundamenta l  cos[tan 1 t ]  0.84
Pt
= 0.784
From the above mentions, all the power factors are reduce
below the fundamental power factor due to the presence of
harmonics in the currents.
Distortion Power Factor, PFdistortion 
1
1  (THD I /100) 2
 0.948
Total Power Factor  PFdisplacement  PFdistortion = 0.84  0.948
= 0.799
This power factor is the condition of without shunt active
filter (SAF).
B. For Feeder-1
In this feeder-1 consist of 1.5 ton induction furnace, 1.0 ton
induction furnace and other linear loads. These loads are
supplied by 300 kVA transformer and supplied voltage is
400V.
Q
PFfundamental  cos[tan 1 t ]  0.83
Pt
Distortion Power Factor, PFdistortion 
1
1  (THD I /100) 2
 0.946
VI. SIMULATION RESULTS
The present system is simulated using the Shunt Active
Filter to reduce Total Harmonic Distortion (THD) in the
current. The values of inductance and capacitance with 0.96 H
and 72.7µF for SAF model are calculated depending upon
required compensated reactive power of the proposed system.
From the simulation results, Fig. 6(a) is the THD of current
without SAF and Fig.6 (b) is the THD of current with SAF for
the whole factory at PCC. As shown in Fig., THD is 33.05%
before using SAF. It is not exist within acceptable level. After
using SAF, THD is reduced to 3.93%. And then, Fig.7 (a) and
7(b) are the THD of Feeder-1 without and with SAF. In this
result THD is 33.76% before using SAF. After using SAF,
THD can reduce to 2.89%. In Fig.8 (a) and (b) are described
the percentage of THD in current for Feeder -2. Before using
SAF the THD is 20.75% it is not exist acceptable level. After
using SAF the THD is reduced to 1.58%. Consequently, THD
without SAF and with SAF id shown in Fig.9 (a) and (b) for
the Feeder-3&4.In this figures; THD of current distortion
(33.11%) is higher than the allowable limit (1.10%) of the
IEEE standard 519.By using SAF, the THD in current can be
reduced to acceptable limits and can improvement power
factors. The improvement of power factors for the proposed
system is shown in Fig.10.
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Fig.6(a) THD of the whole factory at PCC without shunt active filter
Fig.8(a) THD of Feeder-2 without shunt active filter
Fig.6(b) THD of the whole factory at PCC with shunt active filter
Fig.8(b) THD of Feeder-2 with shunt active filter
Fig. 9(a) THD of Feeder-1 without shunt active filter
Fig.7(a) ) THD of Feeder-1 without shunt active filter
Fig.7(b) THD of Feeder-1 with shunt active filter
Fig.9(b) THD of Feeder-3&4 with shunt active filter
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International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Fig.10 Improvement of Power Factor in Proposed system
VII. CONCLUSION
As a conclusion, the effectiveness of Shunt Active Filter
(SAF) has been achieved as the result of harmonics
components reduction that exists in a power system with a
chosen nonlinear load, proposed system. Moreover, shunt
active filter can be compensated the entire harmonic
presented in proposed system by using one equipment. In this
paper, we are able to compensate the harmonic caused by
induction furnaces and DC machine of proposed system and it
provides positive and also improve the power factor.
ACKNOWLEDGMENT
The author would like to express grateful thanks to her
supervisor Dr. Yang Aung Oo, Associate Professor, Department
of Electrical Power Engineering, Mandalay Technological
University for all his help, great guidance and support. The
author wishes to thank to all her teachers from Mandalay
Technological University. The author greatly expresses her
thanks to all persons whom will concern to support in
preparing this paper. The author’s special thanks are sent to
her parents, for their support, encouragement to attain her
destination without any trouble throughout her life.
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