38_286_Study_on_Mitigation_of_Harmonics_by_Using_Passive_Filter_and_Active_Filter (1).pdf

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International Journal of Innovative Research in Computer and Communication Engineering
An ISO 3297: 2007 Certified Organization Vol.3, Special Issue 5, May 2015
International Conference On Advances in Computer & Communication Engineering (ACCE - 2015)
on 5th
& 6th
May 2015, Organized by
Department of CSE, Vemana Institute of Technology, Bengaluru, India
Copyright to IJIRCCE www.ijircce.com 254
Study on Mitigation of Harmonics by Using
Passive Filter and Active Filter
Sahana C B
M.Tech (Power Electronics), Dept. of EE., The oxford College of Engineering, Bangalore, India
ABSTRACT: Harmonics play significant role in deteriorating power quality, called harmonic distortion. Harmonic
distortion in electric distribution system is increasingly growing due to the widespread use of nonlinear loads. With the rapid
developments and use of nonlinear loads, the controlling technique is important over the harmonic. Also voltage and current
waveform to maintain power quality is becoming more important so that both passive and active filters have been used near
harmonic producing loads or at the point of common coupling to block current harmonics. Passive filters still dominate the
harmonic compensation at medium/high voltage level, whereas active filters have been proclaimed for low/medium voltage
ratings. This paper presents an efficient model to compensate the current harmonics using the inverter based Active Power
Filter, Passive Power Filter, and the combination of both. A proposed system is simulating using MATLAB/SIMULINK
power system toolbox.
KEYWORDS: Fundamental frequency, Harmonics, Harmonics filter, linear load, Non-linear load, Passive filter,
Active filter, PID controller
I. INTRODUCTION
In recent days power quality in electrical energy system has become a major challenge for engineers to maintain the
sinusoidal waveform in the system if there is any distortion come in the waveform is known as Harmonic in the system.
Harmonic is a problem arises due to use of Non-linear load or in other word we can say that from solid state component. In
electrical system harmonics is a seen for long time but major of problems related to harmonics are come in frame from past
few years. In electrical power system distribution traditional equipment such as rotating machine produces harmonics due to
uneven distribution of flux in air gap of rotating machine this tends to no sinusoidal voltage & current generation in rotating
machine such as synchronous machine. If we talk about traditional electrical equipment transformer overloading of
transformer is a cause of harmonic generation. Harmonics in power system is defined as current or voltage which is defined
as multiple integer of system frequency or fundamental frequency. Today most of load are producing are producing except of
incandescent bulb light the magnitude of harmonic is varies from load to load. The arise of harmonic current in system is
going to further distorted the system voltage that increasingly affect the system performance & give undesirable situation
such of them are as overheating problems, mechanical & electrical oscillation in alternator & prime movers, failure of
insulation problems, failure of control system & unpredictable behaviour of protection & relay connected in System etc.
Since all these above said problems are severe for the electrical system, so the harmonic mitigation is important for both
point of view of utilities & consumers end. Harmonic filtering technique using passive filters is the one of the most used &
earliest technology present in the system used to address the harmonic mitigation. The filters have been used very widely
because of its very simple designing process & low cost factor.
II. HARMONICS & ITS EFFECTS
Today in modern age fashion of electronics load increased rapidly. These electronics component are very much responsible
for change in the electrical characteristics which are if when analysed with analyser become the evident of change of line
voltage & line current waveform from pure sinusoidal to some other signal form, this distortion in waveform is given as
Harmonic Distortion
The harmonic distortion is a very old problem but previously it was not so severe as today. in the past harmonic distortion
represented the less no of problem due conservative design of power system & equipment & too common use of delta
grounded & wye connection in distribution transformers. Previously it was arose by the saturation of transformers, by

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industrial arc furnaces, some other electrical devices which are a kind of product of arc such as large welding machine,
telephone interference, & increased risk of fault from the overvoltage condition which are developed due to use of power
factor correction capacitors.
A. Basics of Harmonics Theory:
Basically Harmonics in power distribution system is defined as harmonic current or harmonic voltage which is multiple
integer of system frequency or fundamental frequency. Harmonic component must have sinusoidal waveform same as of
fundamental power component say the waveform of voltage & current. In harmonic there is change arises in total voltage or
current waveform & also frequency distortion come in picture, this total distortion disturb whole the system & give failure of
system.
A harmonic component of a sinusoidal component of a periodic waveform that has a frequency equal to an integer multiple
of fundamental frequency or line frequency of system harmonic in power or say voltage or current can then be conceived as
perfectly sinusoidal component of frequency multiple of fundamental frequency which can be seen in figure[1]
B. Harmonic Order:
In the electrical system various type of harmonics are present which are given by their order. Harmonic order or harmonic
number is a reference to the frequency of the harmonic component. The order of harmonics are decided by formula as shown
below [2]
Fh = (h) * fundamental frequency or line frequency
Where h = Integer value
So if we talk about first harmonics of system will be same as the line frequency. Now for the 3rd
harmonics the harmonic
component is given by above formula for the system having frequency of 50 Hz
F3 = 3 * 50 = 150 HZ
Fifth harmonic is similarly given by
F5 = 2 * 50 = 250 HZ
& seventh harmonic can be given as
F7 = 7 * 50 = 350 HZ
So now if we had considered ideal condition that system has frequency of 50 Hz is with a peak value of 100 Ampere current
along the system. This 100 Ampere value is also considered as one per unit. Likewise this per unit the harmonics would have
same waveform of order of (1/3) (1/5) (1/7) of fundamental waveform or amplitude. This behavior of harmonic shown an
inverse law with harmonic component, the system have these harmonics are shown in fig 2 where the whole system
frequency is also affected shown in the waveform.
Fig [1] Resultant waveform of system has 3
rd
5
th
& 7
th
harmonics
In figure the systems current how get impacted by harmonics is shown. The resultant current of the system first of all going
to reduced & second one there is fluctuation problem also arise in system which further may give rise problem such as

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overheating, insulation failure etc.
C. Causes of HARMONICS:
Harmonics are basically arising due to type of load we are using in the system. There are in system two type of load are
present one is linear load which is characterized by have same waveform identical with the line waveform. In other or very
simple way we can say that if there is sinusoidal input given to any load having charectistics of linearity then the resultant
output generated by load will also be sinusoidal. It has been seen that up to 1980‟s the load are of linear type. The other load
is given as nonlinear load which has different waveform than the supply waveform the simple example of nonlinear load is
SMPS (switch mode power supply). In now a day‟s most of loads are of non-linear type & produces harmonics. Only the
load known which fulfils the condition of linear load is given as Incandescent lamp
D. Linear load:
A load is said to be linear if the waveform of voltage & current signals follow each other identifiably or very close to each
other [3]
A very easy way to understand the linear load can be given by the Ohm‟s law which stated that the current (I)
through resistance fed by voltage source (V) is equal to the relation (R) between voltage & resistance which are described by
I (t) = V (t) / R
This relation proves that current & voltage waveform in electrical circuit with linear load look alike. Therefore if the source
is clean or say that there is no distortion in the system then the current waveform will look identical having no distortion as
shown in the figure 2
Fig[2] Waveform with Linear Load
E. Nonlinear load
Nonlinear load are type of load in which the voltage waveform & current waveform does not have same waveform & not
identical with the applied source [figure 3] due to number of reason present in the system. The much known problem of this
is the use of electronic devices & switches. The electronic switches do not conduct load current during the whole power
frequency period but only the fraction of that period. This is the main reason that the load voltage & current are not having
identical waveform. The other thing which we also can say that the system which does not fulfil the Ohm‟s law can be said
Non-linear load.
Among the all the types of nonlinear load which affects the system most are power converter. Uninterrupted power system
(UPS), various types of electric furnaces & etc.
Fig [3] Waveform with Non Linear load

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The causes of harmonics which are come in picture broadly are industrial electronics devices. The current drawn by these
industries from the distribution system are not remaining longer sinusoidal & the resultant of this waveform causes the
occurrence of harmonics in the system.
Types of equipment that generate Harmonics: Harmonic load currents are generated by all non-linear loads. These include:
 For Single phase loads, e.g.
Switched mode power supplies (SMPS)
Electronic fluorescent lighting ballasts
Compact fluorescent lamps (CFL)
Small uninterruptible power supplies (UPS) units
 For Three phase loads, e.g.
Variable speed drives
Large UPS units
Basically whatever the harmonics present in the system is due to non-linear load which are the major source of distortion in power
system component. The other normally possible causes of presence of harmonics in the system are as follows
[4]
:
1: In modern technology use of nonlinear loads have increased rapidly resulting from new technologies such as silicon-
controlled rectifiers (SCRs), power transistors, and microprocessor controls by which a load-generated harmonics produces
in the system.
2:due to presence of nonlinear component present in the system such as rectifier, inverter, dc- to - dc converter, Welding
machine, & arc furnaces & converters.
3: when there is a sudden change occur in load arise there is some distortion come in flux distribution of synchronous
machine
4: speed control device of AC machine which are designed based on semiconductor devices
 Harmonic currents cause problems both on the supply system and within the installation.
 The effects and the solutions are very different and need to be addressed separately; the measures that are
appropriate to controlling the effects of harmonics within the installation may not necessarily reduce the distortion caused on
the supply and vice versa.
F. Effects of Harmonics
Harmonics are a major cause of power supply pollution lowering the power factor and increasing electrical losses. The effect
of harmonic results in premature equipment failure and also cause of requirement of equipment of high rating The voltage
distortion produced in the system is the major issue with the harmonics distribution. The electronics equipment used in the
system usually generate harmonics more than one. In all type of harmonics the tripled harmonics are more severe example of
triplet harmonics are 3rd 9th 15
th [5]
. These harmonics produced bigger problem to engineers because they poses more
distortion in voltage. The effect of triplex harmonics come with overheating in wires, overheating in transformer units & also
may become the cause of end user equipment failure.
Triplex harmonics overheat the neutral conductor of 4 wire system. the neutral have generally no fundamental frequency or
even harmonics but there may be existence of odd harmonics in system neutral conductor & when there is system consist of
triplex harmonics it is become additive. these triplex frequency impact on the system can be understand by this way that even
under balanced load condition on the account of triplex frequency neutral current magnitude reaches up to 1.75 times of
average phase current
[6]
. Under above discussed case if the load of system increase may become cause of failure of
insulation of neutral conductor which further result in the breakdown of transformers winding.

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The important & major effect of Harmonics is further discussed as:
i. Thermal effect on transformers
Transformer is a key device to supply all types of load either for commercial or industrial or residential purpose. As these
service transformers are connected with the large end consumer side so they are attached directly or indirectly with the
various kind of load say linear & non linear both. In modern age industrial & commercial network are very rapidly
influenced by a large or huge amount of harmonic current which produced by variety of nonlinear type loads likes Variable
speed drives, electric furnaces different type of converters etc. in addition of that if we take the case of residential user there
is a lot of Type of personnel & entertaining equipment are which are also a source of harmonic current & harmonic voltage.
ii. Neutral conductor overloading
In single phase power system neutral play a very important role as they carry the return current & complete the circuit. But in
case of harmonics it also becomes the return path for the harmonic current to transformer through neutral connection. for an
unbalanced system the unbalanced current are passed through the neutral & for this purpose we need to balance the system
the size of neutral cable is almost taken equal to its phase cable. Under environment of harmonics the unbalanced current
which is passed through the neutral produces a heat loss in the system which again affects the power quality of distribution
system.
iii. Effect on lines & cables
Harmonic distortion in a distribution system affect the system current & significantly these increased rms current produces
additional heat losses in the system lines & cables
Harmonic distortion in cables affect by increasing the dielectric stress in the cables. This dielectric stress is proportional to
the voltage crest factor which represents the crest value of voltage waveform to rms value of waveform. The effect of this
increased dielectric stress is such that on the cable is shortens the useful life of cable, causes of increased faults, which
ultimately increased the system capital cost & maintenance cost
[7]
.
iv. Thermal effect on rotating machine:
Rotating machine are also affected by harmonics same as transformer. Resistance of rotating machine will goes high if the
frequency of system is high. For this if there is harmonic present in the system have a very rich current value which tends to
produce a heat loss in the rotating machine
[8]
. This overall heat loss will again affect the life of transformer & maintenance
problems.
v. Undesired operation of Fuse
In the environment of harmonic the RMS value of voltage & current may increase. This tendency of increased value of RMS
voltage & current will lead the problem of unexpected operation of fuse in capacitor banks or other arrangement which are
used in the system to make operation of nonlinear load. When if the fuse of one connected phase become fuse then the other
remaining fuse is in operation due to this a stress come on the panel capacitor bank. In this type of condition the system other
point become unbalanced & this will tends to produce the overvoltage on the system & detune the Passive filter in the system
if they are not ready for such type of situation So if we further summarize our above discussion the effect of harmonic affect
by the following given means

Equipment overheating 


Equipment malfunction or operation failure of equipment 


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
Equipment failure 


Communications interference 


Fuse and breaker operation failure 


Process problems 

Problem Caused Harmonic within the installation
 Problems caused by harmonic currents:
1. overloading of neutrals
2. overheating of transformers
3. nuisance tripping of circuit breakers
4. over-stressing of power factor correction capacitors
5. skin effect
 Problems caused by harmonic voltages:
1. voltage distortion
2. induction motors
3. zero-crossing noise
4. Problems caused when harmonic currents reach the supply
G. Remedies to reduces Harmonics
i. Over sizing Neutral Conductors
In three phase circuits with shared neutrals, it is common to oversize the neutral conductor up to 200% when the load served
consists of non-linear loads. For example, most manufacturers of system furniture provide a 10 AWG conductor with 35 amp
terminations for a neutral shared with the three 12 AWG phase conductors. In feeders that have a large amount of non-linear
load, the feeder neutral conductor and panel board bus bar should also be oversized.
ii. Using Separate Neutral Conductors
On three phase branch circuits, another philosophy is to not combine neutrals, but to run separate neutral conductors for each
phase conductor. This increases the copper use by 33%. While this successfully eliminates the addition of the harmonic
currents on the branch circuit neutrals, the panel board neutral bus and feeder neutral conductor still must be oversized.
Oversizing Transformers and Generators: The oversizing of equipment for increased thermal capacity should also be used
for transformers and generators which serve harmonics-producing loads. The larger equipment contains more copper.
iii. Passive filters
Passive filters are used to provide a low impedance path for harmonic currents so that they flow in the filter and not the
supply. The filter may be designed for a single harmonic or for a broad band depending on requirements. Simple series band
stop filters are sometimes proposed, either in the phase or in the neutral. A series filter is intended to block harmonic currents
rather than provide a controlled path for them so there is a large harmonic voltage drop across it. This harmonic voltage
appears across the supply on the load side. Since the supply voltage is heavily distorted it is no longer within the standards
for which equipment was designed and warranted. Some equipment is relatively insensitive to this distortion, but some is
very sensitive. Series filters can be useful in certain circumstances, but should be carefully applied; they cannot be
recommended as a general purpose solution.
iv. Active Filters
The solutions mentioned so far have been suited only to particular harmonics, the isolating transformer being useful only for
triple-N harmonics and passive filters only for their designed harmonic frequency. In some installations the harmonic content
is less predictable. In many IT installations for example, the equipment mix and location is constantly changing so that the
harmonic culture is also constantly changing. A convenient solution is the active filter or active conditioner. The active filter
is a shunt device. A current transformer measures the harmonic content of the load current, and controls a current generator

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to produce an exact replica that is fed back onto the supply on the next cycle. Since the harmonic current is sourced from the
active conditioner, only fundamental current is drawn from the supply. In practice, harmonic current magnitudes are reduced
by 90%, and, because the source impedance at harmonic frequencies is reduced, voltage distortion is reduced.
v. Isolation transformers
As mentioned previously, triple-N currents circulate in the delta windings of transformers. Although this is a problem for
transformer manufacturers and specifies – the extra load has to be taken into account it is beneficial to systems designers
because it isolates triple-N harmonics from the supply. The same effect can be obtained by using a „zig-zag‟ wound
transformer. Zig-zag transformers are star configuration auto transformers with a particular phase relationship between the
windings that are connected in shunt with the supply.
vi. K-Rated Transformers
Special transformers have been developed to accommodate the additional heating caused by these harmonic currents. These
types of transformers are now commonly specified for new computer rooms and computer lab facilities.
vii. Special Transformers
There are several special types of transformer connections which can cancel harmonics. For example, the traditional delta-
wye transformer connection will trap all the tripled harmonics (third, ninth, fifteenth, twenty-first, etc.) in the delta.
Additional special winding connections can be used to cancel other harmonics on balanced loads. These systems also use
more copper. These special transformers are often specified in computer rooms with well-balanced harmonic producing
loads such as multiple input mainframes or matched DASD peripherals.
III. HARMONIC FILTERING TECHNIQUES
Now days the receiver who utilizes the electrical power is supplied through to various electronic substances say AC- DC
converter, Motor speed adjustable unit, various switching mode power supply system & computer process generator. All
above discussed terminology are processed on diode, triode, transistor, thyristor which promote the nonlinearity
characteristics
[9]
& due to this nonlinear function the receiver will be the cause of injecting the harmonic component in the
distribution system & will also affect the other consumer by this pollution of harmonic in system. In general harmonic filter
technology is quite important for the power quality improvement of the system. The harmonic produce in the system is
minimized by the use of various filters that are referring basically as ACTIVE FILTER & PASSIVE FILTER.
A. Introduction to PASSIVE FILTER
Harmonic distortion in the system is very vast problem for the entire electrical power researcher & they continuously worked on the
mitigation of harmonic component in the system to make system neat& clean & consumer avail electrical utilities in very
determinant, with high performance and high efficiency. Passive filters are very much helpful for mitigation of harmonic
component & used traditionally. Passive filter are used for the mitigation of harmonic in the electrical society for last 3 decades &
there is a continuous development has been reported in this technique for the better use of filter & convert the filter more useful to
achieve the optimum approach to utilization with reduced rating & cost. The use of passive filter in the mitigation of harmonic.
Passive filter are used for the mitigation of harmonic component & also provide the reactive power compensation in the system to
improve the power quality so by mean of this power filter helps the system by two means one is to improve the system power
quality & improve reactive power problem so reduced the need of capacitor for supplying extra needed KVAR. The performance of
passive filter depends mainly on the system source impedance.
B. Classification of Passive filter
The classification of Passive filter is done on the type of harmonic generation component source present in the system &
passive component sys resistor, inductor & capacitor connected in the system & are given as
[10]

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1: PASSIVE SERIES FILTER
2: PASSIVE SHUNT FILTER
3: PASSIVE HYBRID FILTER
A very classical type of passive filter [4] is shown in the figure where filter is connected in the parallel with distribution
system through power common coupling point having nonlinear load characteristics
Fig [4] Schematic arrangement of passive filter
Fig.4 shows a classical shunt passive filter is connected the power system through common coupling point (PCC). Because
of using non-linear load, the load current is highly non-linear in nature. The compensating current which is the output of the
shunt passive filter is injected in PCC, by this process the harmonic cancellation take place and current between the sources
is sinusoidal in nature. The passive filter is popular in cancellation of harmonic current in power system to control this
process.
A. Passive series filter
The system which come with the voltage source type harmonic which are the bi product of diode rectifier with R-C
connected load(figure 5) it is prefer to use the series type passive filter as considered as potential remedy of harmonic
mitigation. A passive type series filter has property of purely inductive type or LC tuned characteristics. The main
component of passive series filter is AC line reactor & DC link filter. The operating principle of series passive filter is given
by these two component connected in series that AC line reactor improve system magnitude of inductance in system that
alters the path of current drawn in the rectifier circuit. These whole processes of offering magnitude in the system make
system current waveform more continuous compare to without use of filter technology in the system
[11]
. Therefore system
harmonic distortion will be going to reduced compare to previous.
Fig 5 Schematic diagram of series connected passive filter
C. Passive shunt filter
It is the most common method for the cancellation of harmonic current in the distribution system. Passive harmonic filter are
basically designed on principle of either single tuned or band pass filter technology. As the name suggests shunt type filter
are connected in system parallel with load. Passive filter offer a very low impedance in the network at the tuned frequency to
divert all the related current & at given tuned frequency. Because of passive filter always have tendency of offering some

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reactive power in the circuit so the design of passive shunt filter take place for the two purpose one is the filtering purpose &
another one is to provide reactive compensation purpose of correcting power factor in the circuit at desired level. The
advantage with the passive shunt type filter is that it only carry fraction of current so the whole system AC power losses are
reduced compare to series type filter. The given figure [6] shows the schematic diagram of converter system connected with
shunt passive type filter which are simply employed ever connection in distribution system have R-C load in system
Fig [6] Shunt filter connection
IV. DESIGN OF PASSIVE AND ACTIVE FILTER
In general filter used in distribution system is Passive shunt type filter. In previous discussed chapter we had already studied that
shunt passive filter consists of Simple combination of passive component resistor inductor & capacitor in the circuit. The designing
of these components should be so well that they will precisely employ for each specified harmonic frequency for which it has been
tuned
[12]
. Passive harmonic filter are used in the society are of single tuned & band pass filter type
[13]
. Passive filter designed in
the same manner in single tuned connection or high pass filter connection which are given in following figure [7]
Fig [7] Different type of passive filter
a. Single tuned filter
Single tuned filters are the probably most common type of filter which is used in industry broadly for the harmonic
mitigation. The basic principle of using passive filter is that on the tuned frequency filter will offer low impedance to current
through which harmonic current will tends to divert in the system. One more advantage of employing passive filter is that it
comes with the property of reactive power compensation
[14]
. A very simple arrangement of single tuned filter is shown in
the figures [8] which also give the connection arrangement used in the single tuned filter designing
Fig [8] Simple connection diagram of single tuned filter

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As discussed & easily can seen from the figure that single tuned filter are the simple series connection of R-L-C component
& L-C component. The equation of resonant frequency for single tuned frequency is given by following equation
Where
f0= Frequency at resonant in Hertz L=inductance of Filter in Hennery C = Capacitance of Filter
Whenever a single tuned harmonic filter is connected with the nonlinear load will look alike the figure of circuit. As from the
figure it is easily seen that there is some inductance present in the system prior to system Connected filter which is known as
source filter (Ls). This source impedance will always have a tendency of affecting the system resonant condition. This total
source impedance will be so much has impact that resonant condition of system will be just before the tune frequency &
operate the filter with some neighbouring frequency too.
They usually custom designed for the application. However, performance is limited to a few harmonics and they introduce
resonance in the power system Also, a separate filter is necessary for each harmonic frequency. Among different new filters
to improve harmonic problem is active power filter. The idea of using active power filter is compensate for current and
voltage disturbances in power distribution system but their practical development was made possible with the good control
strategy in reducing harmonic distortion as well as with cost reduction. . It also introduces resonance that can move a
harmonic problem from one frequency to another Through power electronics, active filter produces current or voltage
components, which cancel the harmonic components of the nonlinear loads supply lines, respectively. These active filters
relatively new and a number of different topologies are being proposed. This paper describes the simulation results an
extensive investigation to evaluate the performances between passive and active power filters
V. BASIC PRINCIPLE OF ACTIVE FILTER
The basic concept of APF is explained in fig9
IL = IS + IF (1)
The load current having fundamental and harmonic content, and IF is the harmonic compensating current.
IL + IH = IS + IH (2)
Filter provide harmonic requirement of the load
IL + IH = IS + IH
(3) IL= IS (4)
Thus the supply current represents the fundamental waveform input output harmonics. Fig.9. shows the configuration of
active shunt filter with non-linear load and the full bridge converter. which is almost widely used to eliminate current
harmonics, reactive power compensation and balancing the unbalanced currents.
Fig.9

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A. Basic Block diagram
Fig10
Fig10 shows the basic circuit of APF including inverter having an energy storage capacitor on dc side. Pulse width
modulation (PWM) is employed to generate gating pulses to the switches of APF. The dc based load fed from diode bridge
rectifier with a capacitor is a non-linear load on the ac mains. The proposed APF is to eliminate harmonics and to improve
the power factor of supply.
i. Voltage fed inverter
A single phase voltage source IGBT bridge with an energy storage capacitor on dc side, connected in parallel with the load-
thus forming a voltage fed inverter. The full bridge inverter is built by four IGBTs that chosen according to their suitable
ratings. Anti-parallel diodes are connected across these power switches in term of protection and providing power conversion
in reverse direction in order to recharge the dc capacitor whenever its level goes lower than a reference value. Large size
capacitor is connected to the inverter such that constant level of voltage could be maintained over each switching cycle.
ii. Interface Filter
The filter provides smoothing and isolation for high frequency components. Control of the injected current wave shape is
limited by the switching frequency of the inverter and the available driving voltage across the interfacing inductance. The
driving voltage across the interfacing inductance determines the maximum di/dt that can be achieved by the filter. This is
important because high values of di/dt may be needed to cancel higher order harmonic components. A large value of
interfacing inductance is better for isolation but it limits the ability of an active filter to cancel higher order harmonics.
iii. PWM Controller
A simplified PID (Proportional-Integral-derivative) control of the dc capacitor average voltage is used to generate reference
source current in phase with ac source voltage to result in unity power factor of the source current. The pulse width
modulation (PWM) is employed to generate gating signal for IGBTs to control the phase and magnitude of the inverter
output. PWM is chosen as a controller in this work due to its ability to reduce the distortion factor and lower order of
harmonics as well besides that the phase and the magnitude of the full-bridge inverter can be easily changed.
iv. Non-linear loads
In this paper typical diode rectifier with capacitor-resistive load is taken as non-linear load on the ac main for simulation as
shown in Fig
VI. PROPOSED CONTROL SCHEME
As shown in Fig the sensed dc voltage of the APF is compared with its set reference value in the error detector. The voltage
error is processed in the P-I voltage controller. Its output is limited to the maximum permitted value. This output of the
voltage controller is taken as peak value of supply current.

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Fig.6
A. Operation of controller loop
Being connected to the PCC (Point of Common Coupling), during non-switching operation, APF charges dc capacitor via
diodes to the maximum value of system voltage. Voltage of the dc capacitor experiences the second harmonic ripple of the
ac mains fundamental frequency. Thus dc storage capacitor voltage is symmetric about half the period of the ac cycle under
steady state operating condition. This voltage is averaged over the half cycle of ac mains for the use in PID voltage
controller. This PID voltage controller will try to maintain constant dc capacitor voltage to a reference value. For that, it will
draw the necessary power from ac source to meet the losses in the APF such as switching loss, capacitor leakage current, etc.
in addition to the real power the load
Under any disturbance in the load (either increase or decrease), the load will try to draw new increased or decreased value of
current. This increased load current will be supplied immediately from the APF resulting in decreased energy storage on dc
capacitor. It reduces the average voltage across dc capacitor. This reduction in dc capacitor voltage of the APF will activate
the PID controller and increases the supply current. This increased source current tries to restore the stored energy of the
capacitor in addition to increased load active power. Supply current settles to new steady state value within few cycles. Vice-
versa operation will be performed for load current decrease. Since the corrective action of the PID voltage controller is taken
within the half cycle of the ac mains it results in fast response.
System Parameters-
Vdc=230V Lc = 1 µH, Cc =100mf, RL = 100Ω,
Vdcref = 600 V, Kp = 180, Ki = 320, kd=1, Ts=1µs.
VII. SIMULINK MODEL FOR SIMULATED CIRCUIT WITHOUT FILTER
Fig.7. 1(a) Fig.7. 1(b)

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Fig.7. 1(c)
Fig.7. 1(a) Simulation circuit without using filters
(b) Simulation results for current
(c) THD value
VIII. INTRODUCTION TO PASSIVE FILTER
The passive filters are used to mitigate power quality problems in ac-dc converter with R-C load. Moreover, apart from
mitigating the current harmonics, the passive filters also provide reactive power compensation, thereby, further improving
the system performance. For current source type of harmonic producing loads, generally, passive shunt filters are
recommended. These filter apart from mitigating the current harmonics, also provide limited reactive power compensation
and dc bus voltage regulation. However, the performance of these filters depends heavily on the source impedance present in
the system, as these filter act as sinks for the harmonic currents. On the other hand, for voltage source type harmonic
producing loads, the use of the series passive filters is recommended. These filters block the flow of harmonic current into ac
mains, by providing high impedance path at certain harmonic frequencies for which the filter is tuned. Moreover, the
harmonic compensation is practically independent of the source impedance. But, passive filter suffer due to the reduction in
dc link voltage due to the voltage drop across the filter components at both fundamental as well as harmonic frequencies.
This chapter presents a detailed investigation into the use of different configurations of passive filter such as passive shunt
filter and passive series filters. The advantages and disadvantages of both configurations are discussed. It is observed that
both these configuration fail to meet the IEEE standard 519 guidelines under varying load conditions. A novel configuration
of passive hybrid filter (a combination of passive shunt and passive series filter) is designed and developed for power quality
improvement. The main attraction of this configuration is that it can achieve the improved power quality even under varying
load conditions, its rating is less and it can maintain that dc link voltage regulation within certain limits. The prototypes of
these passive filters are developed and that test results are presented to verify the simulated results. Finally, a comparison of
different power quality aspects in different configurations of passive filters is also presented for ac-dc converter with R-C
load.
Classification of passive filters
Depending on the connection of different passive components, the passive filters can be broadly classified in three categories
as given below.

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A. Passive Shunt Filter
Fig.8.1 schematic diagram of a passive shunt filter
Fig.8.1 shows the schematic diagram of a passive shunt filter connected at input ac mains of ac-dc converter with R-C load.
This is the most commonly used configuration of passive filters. In this configuration different branches of passive tuned
filters (low pass and high pass) tuned for the more dominant harmonics are connected in parallel with the diode rectifier with
RC load. It consists of a set of low pass tuned shunt filters tuned at 5th and 7th harmonic frequencies and high pass tuned for
11th harmonic frequency. This passive filter scheme helps in sinking the more dominant 5th and 7th and other higher order
harmonics and thus prevents them from flowing into ac mains. The diversion of harmonic current in the passive filter is
primarily governed by the source impedance available in the system. The higher value of source impedance offers better
performance of the passive filter.
B. Passive Series Filter
Fig.8.2 schematic diagram of a passive series filter
For voltage source type of harmonic loads (such as diode rectifier with R-C load filter), passive series filter is considered as a
potential remedy for harmonic mitigation. Fig.8.2 shows the schematic diagram of a passive series filter connected at input
ac mains of ac-dc converter with R-C load. Here, the different tuned branches of passive filters are connected in series with
the supply and the diode rectifier. Passive series filter connected at input ac mains. It consists of a set of low block tuned
shunt filter tuned at 5th and 7th harmonic frequencies and high block tuned filter for 11th harmonic frequency. These passive
filters blocks most dominant 5th, 7th and other higher order harmonics and thus prevents them from flowing into ac mains.
Here, the performance of the series filter is not much dependent on the source impedance. However, it results in reduction in
dc bus voltage due to voltage drop across filter components.

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C. Passive Hybrid Filter
The use of passive shunt filter creates the problem of voltage regulation at light loads. It also increases the dc voltage ripple
and ac peak current of the rectifier. On the other hand, passive series filter suffers from lagging power factor operation as
well as the voltage drop across the filter components both at fundamental frequency as well as harmonic frequencies. To
overcome these drawbacks, a combination of both these configurations is presented as passive hybrid filter. This
configuration is able to supplement the shortfalls of both these passive filters and simultaneously it results in improvement in
harmonic compensation characteristics for varying load condition even under stiff and distorted ac mains voltage.
D. Basic circuit with using passive series filter
Fig.8. 2(a) Fig.8. 2(b)
THD values:
Fig.8. 2(c)
Fig.8. 2(a) Simulation circuit without using filters
(c) THD value

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E. Simulated circuit with Passive shunt filter
Fig.8.3 (a) Fig.8.3 (b)
THD values:
Fig. 8.3(c)
Fig.8. 3(a) Simulation circuit using Passive shunt filters (b) Simulation results for current
(c) THD value

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IX. INTRODUCTION TO ACTIVE FILTER
Active power filters (APF)
Harmonic distortion in power distribution systems can be suppressed mainly by, passive and active filtering. The passive filtering is
the simplest conventional solution to mitigate the harmonic distortion. Passive provide resonance and its performance is limited to
few harmonics for the elimination of higher order harmonic separate filter is required these are the main disadvantage of passive
filters. Thus uses of passive elements do not always respond correctly to the dynamics of the power distribution systems. Passive
filters are known to cause resonance, thus affecting the stability of the power distribution systems. Frequency variation of the
power distribution system and tolerances in components values affect the passive filtering characteristics. As the regulatory
requirements become more stringent, the passive filters might not be able to meet future revisions of a particular Standard. This
may require a retrofit of new filters.
Remarkable progress in power electronics had spurred interest in Active Power Filters (APF) for harmonic distortion mitigation.
Active filtering is a relatively new technology, practically less than four decades old. The basic principle of APF is to utilize power
electronics technologies to produce specific current components that cancel the harmonic current components caused by the
nonlinear load. APFs have a number of advantages over the passive filters. First of all, they can suppress not only the supply
current harmonics, but also the reactive currents. Moreover, unlike passive filters, they do not cause harmful resonances with the
power distribution systems. Consequently, the APFs performances are independent on the power distribution system properties.
Active filtering is a relatively new technology, practically less than four decades old. There is still a need for further research and
development to make this technology well established.
Classification of active filters
Depending on the connection of different passive components, the active filters can be broadly classified in three categories
as given below
a. Shunt Active Power Filter
The purpose is to cancel the load current harmonics fed to the supply. It can also contribute to reactive-power compensation and
balancing of three-phase currents, as mentioned above. Parallel filters have the advantage of carrying only the compensation current
plus a small amount of active fundamental current supplied to compensate for system losses. It is also possible to connect several
filters in parallel for higher currents, which makes this type of circuit suitable for a wide range of power ratings.
b. Series Active Power Filter
The active filter in this configuration produces a PWM voltage waveform which is added or subtracted, on an instantaneous basis,
to/from the supply voltage to maintain a pure sinusoidal voltage waveform across the load. The inverter configuration
accompanying such a system is a voltage-fed inverter without any current-control loops. Series active filters are less common
industrially, than parallel active filters. This is because of the main drawback of series circuits, namely that they have to handle
high load currents, which increases their current rating considerably compared with parallel filters, especially in the secondary side
of the coupling transformer. The main advantage of series filters over parallel ones is that they are ideal for eliminating voltage-
waveform harmonics, and for balancing three-phase voltages. This, in fact, means that this category of filter is used to improve the
quality of the system voltage for the benefit of the load. It provides the load with a pure sinusoidal waveform, which is important
for voltage-sensitive devices.
c. Hybrid Active Power Filters
Technical limitations of conventional APFs can be overcome with hybrid APF configurations. They are typically the combination
of basic APFs and passive filters. Hybrid APFs, inheriting the advantages of both passive filters and APFs provide improved
performance and cost-effective solutions. The idea behind this scheme is to simultaneously reduce the switching noise and
electromagnetic interference. The idea of hybrid APF has been proposed by several researchers. In this scheme, a low cost passive
high-pass filter (HPF) is used in addition to the conventional APF. The harmonics filtering task is divided between the two filters.
The APF cancels the lower order harmonics, while the HPF filters the higher order harmonics. The main objective of hybrid APF
therefore is to improve the filtering performance of high-order harmonics while providing a cost-effective low order harmonics
mitigation.

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D. Simulated circuit using active series filter
Fig.9. 1(a) Fig.9. 1(b)
THD Values:
Fig.9.1(c)
Fig.9.1(a) Simulation circuit without using filters
(c) THD value

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International Journal of Innovative Research in Computer
and Communication Engineering
(An ISO 3297: 2007 Certified Organization)
Vol. 2, Issue 11, November 2014
E. Simulated circuit with Active shunt filter
Fig.9.2 (a) Fig.9.2 (b)
THD Values:
Fig. 9.2(c)
Fig.8. 5(a) Simulation circuit using Active shunt filters (b) Simulation results for current
(c) THD value

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F. Comparison table for basic circuit using passive filter and active filter using PID controller
Circuit 3rd
order 5th
order 7th
order 9th
order 11th
order THD
Basic Circuit
without filter 43.53% 37.47% 27.86% 12.15% 6.15% 63.53%
Passive series
filter 41.49% 4.18% 6.41% 2.56% 2.20% 45.68%
Passive shunt
filter 7.30% 4.05% 2.56% 1.67% 1.09% 10.21%
Active Series
filter 4.45% 2.57% 1.73% 1.24% 0.92% 6.90%
Active Shunt
filter
1.84% 1.10% 0.77% 0.59% 0.47% 3.13%
X. CONCLUSION
This paper has presented a brief idea about harmonic & their consequences effect on the distribution & transmission
system here we also study the basic harmonic mitigation technique which is now a day‟s applying in fashion. Here we
presented a brief idea about the designing process of passive filter and active filter with two types of filter for the
mitigation of harmonic in the system. It improves the power quality and THD and gives us the pure sinusoidal wave. Active
power filters are the emerging devices, which can perform the job of harmonic elimination properly. First the harmonic
disturbances are detected from the power line using transducers, and then harmonic waveform is separated from the
fundamental sine wave using reference signal estimation techniques. The PWM signals for controlling purpose are then
generated using any one of control signal generation schemes. Thus an Active shut filter will provide harmonic elimination
with better controlling methods compared to passive filters.
REFERENCES
1. J. Arrillaga, D. A. Bradley, and P. S. Bodger, “Power System Harmonics by Frequency Domain Approaches”. New York: Wiley, 1985
2. Acta Universitaties Surat, Gujarat, India “Design And Simulation of harmonic mitigation in medium voltage power distribution system Single
Phase Shunt” Sapientiae Electrical, 1 (2009)
3. Zamora, A. J. Mazon. P. Eguia, I. Albizu, K. J. Sagastabeitia, E. Fernandez, “Harmonic Mitigation, Power Factor Correction & Energy Saving
with Proper Transformer & Phase Shifting Techniques ”, IEEE Power Tech Conference, June 2003
4. Javier Napoles,Alan J. Watson, , Jose J. Padilla,Jose I. Leon, Leopoldo G. Franquelo, Patrick W. Wheeler,and Miguel A. Aguirre, “Selective
Harmonic Mitigation Technique for Cascaded H-Bridge Converters With Nonequal DC Link Voltages”ieee transactions on industrial
electronics, vol. 60, no. 5, may 2013
5. IEC Sub-Committee 77A report, ΄΄Disturbances Caused by Equipment Connected to the Public Low-Voltage Supply System Part 2 : Harmonics
΄΄, 1990 (Revised Draft of IEC 555)

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6. Takahashi, and Y. Omura, “High power active filter using LC tuned filter”, JIEE Trans. Ind. Appl. D 112 (9), 823–828 (1992), (in Japanese )
7. Bhattacharya et al, ΄΄Hybrid Solutions for improving Passive Filter Performance in high power Applications΄΄, IEEE, Trans. on Industry
Applications, Vol. 33, No. 3, May/June 1997, pp. 732-747.
8. Akagi, ΄΄Control Strategy and site selection of a shunt active filter for damping of harmonies propagation in power distribution systems ΄΄, IEEE
Trans. on Power Delivery, Vol. 12, Jan. 1997, pp.354-363.
9. Lecture notes: harmonic analysis Russell Brown,Department of mathematics University of Kentucky Lexington, KY 40506-0027 12 June 2001
10. Harmonics, Sources, Effects and Mitigation Techniques Ali I. Maswood and M.H. Haque School of EEE, Nanyang Technological University
Second International Conference on Electrical and Computer Engineering ICECE 2002, 26-28 December 2002, Dhaka
11. Roger C.Dugan, Mark F. McGranaghan, Surya Santoso and H.Wayne Beaty, Electrical Power System Quality, McGraw Hill, pp 324-425,
2002. [H. Fujita and H.Akagi, “A practical approach to harmonic compensation in power system-series connection of passive, active filters,”
IEEE Trans. Ind. Applicat., vol. 27, no. 6, pp. 1020–1025, Nov./Dec. 1991.
12. Karuppanan P and Kamala kanta Mahapatra “PID with PLL Synchronization controlled Shunt APLC under Non-Sinusoidal and Unbalanced
conditions” National Power Electronics Conference (NPEC) Proceedings, IIT-.
BIOGRAPHY
SAHANA C B is a Student in the M.Tech Power electronics Department, The oxford college of engineering,
Bangalore. She receive Master of Technology (M.TECH) degree in 2015 from VTU, Karnataka, India.

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