Study on Mitigation of Harmonics by Using Passive Filter ... - IJIRCCE

ISSN(Online): 2320-9801 ISSN (Print): 2320-9798

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

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 Copyright to IJIRCCE

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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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 3 rd 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.

rd th

th

Fig [1] Resultant waveform of system has 3 5 & 7 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 Copyright to IJIRCCE

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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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 Copyright to IJIRCCE

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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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 [4] system component. The other normally possible causes of presence of harmonics in the system are as follows :

1: In modern technology use of nonlinear loads have increased rapidly resulting from new technologies such as siliconcontrolled 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 th [5] triplet harmonics are 3rd 9th 15 . 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 [6] average phase current . 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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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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 [7] ultimately increased the system capital cost & maintenance cost . 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 [8] produce a heat loss in the rotating machine . 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  Copyright to IJIRCCE

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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India  

 

 

 

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 Copyright to IJIRCCE

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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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 deltawye 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 [9] characteristics & 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 & [10] passive component sys resistor, inductor & capacitor connected in the system & are given as


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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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 [11] system current waveform more continuous compare to without use of filter technology in the system . 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 Copyright to IJIRCCE

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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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 [12] [13] tuned . Passive harmonic filter are used in the society are of single tuned & band pass filter type . 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 [14] comes with the property of reactive power compensation . 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 Copyright to IJIRCCE

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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 Copyright to IJIRCCE

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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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 loadthus 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. Viceversa 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 ParametersVdc=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) Copyright to IJIRCCE

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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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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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 (b) Simulation results for current (c) THD value Copyright to IJIRCCE

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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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 suppl y 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 voltagewaveform 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. Copyright to IJIRCCE

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on 5th & 6th May 2015, Organized by Department of CSE, Vemana Institute of Technology, Bengaluru, India 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 (b) Simulation results for current (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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Vol. 2, Issue 11, November 2014

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%

1.84%

1.10%

0.77%

0.59%

0.47%

3.13%

Active Shunt filter

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. 2. 3. 4.

5.

J. Arrillaga, D. A. Bradley, and P. S. Bodger, “Power System Harmonics by Frequency Domain Approaches”. New York: Wiley, 1985 Acta Universitaties Surat, Gujarat, India “Design And Simulation of harmonic mitigation in medium voltage power distribution system Single Phase Shunt” Sapientiae Electrical, 1 (2009) 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 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 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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Vol. 2, Issue 11, November 2014 Takahashi, and Y. Omura, “High power active filter using LC tuned filter”, JIEE Trans. Ind. Appl. D 112 (9), 823–828 (1992), (in Japanese ) 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-. 6. 7.

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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