Design and simulation ofdifferent harmonic mitigation techniques PROJECT MENTOR: Mr. AKHILESH ARVIND NIMJE SUBMITTED BY: PRANAV SIDDHARTH NISHITH MAYANK HARISH V K VIKASH KUMAR PARTHJEET 1 | Page 807072 807066 807037 907225 807047 CONTENTS: OBJECTIVE INTRODUCTION STATEMENT OF PROBLEM LITERATURE REVIEW HARMONICS MITIGATION AND PASSIVE FILTER TUNED FILTER DESIGN HARMONIC MEASUREMENT WORK ALREADY DONE REFFERENCE 2 | Page Pg-3 Pg-3 Pg-3 Pg-4 FILTER Pg-6 Pg-7 Pg-8 Pg-10 Pg-11 Pg-11 In this project how the capacitor bank parameters contribute to develop the harmonics and recalculating the value of the capacitor bank can help resolve the system harmonics. If the equipments are not properly designed or rated. to convert utility AC power to regulated DC power. Statement of Problem This project involves in designing the harmonic filter to eliminate the harmonic from the system. In depth analysis is performed and mathematical model and software simulation for passive and active harmonic filter is developed. In this project. in depth study of power system analysis is required. This increases line current and can limit the available capacity of branch circuits. This project will look at causes and effects of harmonics in power systems. power systems are designed to operate at frequencies of 50 or 60Hz. study of power quality and detailed analysis of harmonics is performed.OBJECTIVE To study the harmonic filtering techniques used for mitigation on harmonics in modern power system. INTRODUCTION The increased use of nonlinear electronic equipment has become a concern in most utility power systems. To eliminate this harmful effect. . In addition. Hence. For active filter ADAPTIVE HYSTERESIS CURRENT CONTROLLER form will be used. In the first phase passive filter and in the next phase active filter is designed and simulated via many simulation software available. 3 | Page . Although certain types of loads produce current and voltage signal with frequencies that are integer multiples of the 50 or 60 Hz fundamental frequency. These higher frequencies are called electrical pollution that is known as power system harmonics. equipment will often malfunction when harmonics are present in an electrical system and that equipment can be personal computer in business environment or an ultrasonic imaging machine in a hospital. Normally. These switching regulators and switch mode power supplies generate high third and fifth harmonic current. harmonics analysis of a power system forms an important aspect of a reliable system design. Modern personal computers and other information technology equipments utilize “switching regulators” or switch mode power supplies. Harmonics analysis involved the calculation of system parameters. Nonlinear loads draw current discontinuously during the cycle of the input voltage waveform and produce low power factors when harmonics are taken into account. In passive filter design a single tuned shunt notch filter is to be designed. harmonic currents can cause heating in utility and facility transformers. evaluating filter duty requirements. in nonlinear circuits current is not proportional to the applied voltage. That is 50 Hz and the multiples that are 100Hz. Figure 1. filter reactor size. harmonic currents and voltage parameters. As we can see the voltage is perfectly sinusoidal but the resultant current waveform is distorted. 4 | Page . LITERATURE REVIEW Introduction In linear circuits current is directly proportional to the voltage. Figure 1 shows this concept by applying voltage to a nonlinear resistor where the voltage and current vary as shown in the curve. 150Hz. 200Hz. The distorted waveform can be a sum of sinusoidal signals. The sum of the sinusoidal is called the Fourier series. Here the fundamental frequency is the frequency of the power system. This multiple is called a harmonic of fundamental. RMS currents and kVAR values then compared with the standard limitations. RMS voltage. fundamental duty requirements. harmonic duty requirements. Now as we increase the voltage by just few percentages may cause the current to double the value and takes the different shapes. frequency responses. capacitor bank size.Passive filter design The harmonic analysis of power system involves the calculation of power factor. third. When the waveform is identical. Figure 2 shows Fourier series of a distorted waveform. The combine waveform shows the result of adding the harmonics on to the fundamental. Calculation of the peak voltage. This is the source of most harmonics in a power system. However. fourth and fifth harmonics respectively. 250Hz called second. it can be shown as a sum of pure sine waves where the frequency of each sinusoid is an integer multiple of the fundamental frequency of the distorted wave. In utility distribution feeders and industrial plant power systems. In nonlinear load. Harmonics Generation There are different types of loads that generate harmonics in power systems. Figure 3 5 | Page . That means the bulk of the current flows in to the source. the main tendency is for the harmonic currents to flow from the harmonic producing load to the power system source. These loads are not constant impedances during the entire cycle of the applied sinusoidal voltage. For example. wind and solar power generation. the applied sinusoidal voltage does not result in a sinusoidal flow of current. The impedance of the power system is normally the lowest impedance seen by the harmonic currents. The power quality meters can be used to measure the harmonic currents in each branch starting at the beginning of the circuit and trace the harmonics to the source.Figure 2. This is shown in Figure 3. The source of harmonics can be located by using this general tendency of the harmonic current flow. The linear time-invariant loads are designed such a way so that the sinusoidal voltage results in a sinusoidal flow of current. the current increases in direct proportion. The transformers and rotation machines are the examples of this kind of loads when operated in normal condition. These loads have constant steady-state impedances during the applied sinusoidal voltage. When the voltage is increased. Heating effects: Harmonic current flowing in the circuits cause heating effects in the conductors.Modify the system frequency response to avoid harmful interaction with harmonic current. the dielectric stress and load disruptions. are negative sequence or backward rotating and it can increase losses by inducing even higher frequency currents in machine rotors. the thermal stress.Find the nonlinear load and reduce the harmonic current . There are two approaches to mitigate harmonic problems in order to improve the power quality problems. Harmonics Mitigation and Filters The harmonics is becoming a bigger concern now a day with the increase nonlinear load in the power system. It means that to ensure the equipment must be less sensitive to power disturbances. There are multiple ways to control the harmonics as follow: . Some resonance can be dangerous if the magnification is large because of high circuit Q-factor or low damping. notably the 5th. protections systems and signaling circuits due to electromagnetic induction or to the flow of the ground currents. Interference: Harmonics can cause interference to communications systems. Some harmonics. Especially eddy current losses are proportional to the square of the frequency.Add filter to remove the harmonic current or block the harmonic current from entering to the system . Resonance: Harmonics generated in one part of circuit may increase the resonance effects in another part of the circuit.Effect of Harmonics Harmonics practically effect to every equipment in the power system. The first approach is called load conditioning. The effect of voltage distortion is divided in three major categories. Even harmonics: Even harmonics may cause asymmetrical magnification and can lead to saturation. Some more adverse effects of harmonics listed as follows: Malfunction in electronics devices and computer equipments Errors in measurements Lamp flicker when harmonic pulses involved Blowing out of small auxiliary devices like fluorescent lamp capacitors. allowing the operation under significant voltage or current distortion. is to install line-conditioning systems that suppress the power system disturbances. 6 | Page . The second approaches are very interesting where the passive and active power filters are connected to line system either in series or shunt configurations. Secondly. their performance is limited to a few harmonics and they can introduce resonance in the power system. PASSIVE FILTERS Passive filters are inductance. They are usually custom designed for the application. they have the disadvantage of potentially interacting adversely with the power system. and it is important to check all possible system interactions when they are designed. Passive filters are relatively inexpensive compared with other methods for eliminating harmonic distortion. However. capacitance. a separate filter is necessary for each harmonic frequency. However. and resistance elements configured and tuned to control harmonics.Passive filters have been most commonly used to limit the flow of harmonic currents in distribution systems. the active filter produces current or voltage components. Passive filters work efficiently when they are located closer to harmonic generators 7 | Page . which cancel the harmonic components of the nonlinear loads supply lines. Among the different new filters to improve harmonic problem is active power filter. respectively. The idea of using active power filter is to compensate for current and voltage disturbances in power distribution system but their practical development was made possible with the good control strategy in reducing total harmonic distortion as well as with cost reduction. Passive filtering techniques that make use of Single or double-tuned filters providing low impedance path to harmonic currents at certain frequencies or high or band-pass filters (damped filters) that can filter harmonics over a certain frequency bandwidth. Through power electronics. It also not introduces resonance that can move a harmonic problem from one frequency to another. Also. In reality.( nonlinear loads). which is the intrinsic resistance of the series reactor sometimes used as a means to avoid filter overheating. there will always be a series resistance. Passive filters always provide reactive compensation to a degree dictated by the voltampere size and voltage of the capacitor bank used. The resonant frequency must be safely away from any significant harmonic or other frequency component that may be produced by the load. they can in fact be designed for the double purpose of providing the filtering action and compensating power factor to the desired level. Tuned filter design Tuning a capacitor to a certain harmonic requires an additional reactor at the tuned harmonic. Passive filter design must take into account expected growth in harmonic current sources or load reconfiguration because it can otherwise be exposed to overloading. in the absence of a physically designed resistor. If more than one filter is used — for example. All harmonic currents whose frequency coincides with that of the tuned filter will find a low impedance path through the filter. sets of 5th and 7th or 11th and 13th branches — it will be important to remember that all of them will provide a certain amount of reactive compensation. Filters are commonly tuned slightly lower than the harmonic frequency for safety. The reactive power absorbed by the reactor is 8 | Page . which can rapidly develop into extreme overheating and thermal breakdown. Passive filter is a series combination of an inductance and a capacitance. The capacitor should withstand the total voltage across its terminals. Determine the value of the capacitance.98 or higher.The reactive power delivered by the capacitor is A series tuned filter is designed to trap a certain harmonic by adding a reactor to an existing capacitor. Design steps of the following single-tuned series filter is as follows. Q. Power factor compensation is generally applied to raise power factor to around 0. Calculate the reactor resistance for a specified quality factor. The characteristic reactance 9 | Page . QC to improve the power factor and to eliminate any penalty by the electric power company. Evaluate the capacitor reactance at fundamental frequency Calculate the reactor size providing the resonance. the resistance of a single-tuned harmonic filter is the intrinsic resistance of the reactor. A high THD value for input Current may not be of significant concern if the load is light.m. A large Q value implies a prominent valley at the resonant (tuning) frequency of a filter and therefore the trapping of the largest amount of harmonic frequency. R can be favorably used to vary the quality factor of the filter and provide a way to control the amount of desired harmonic current through it. THD is defined as the root mean square (r. voltage. since the magnitude of the harmonic current is low. i. Filter impedance The following points summarize the relevant quality factor aspects in single-tuned filters: Typically.s. N is the maximum harmonic order to be considered and V1 is the fundamental line to neutral r.e.s. even though its relative distortion to the fundamental 10 | P a g e .m. Lesser THD allows the components in a equipment to produce a more accurate reproduction. Harmonic measurement Total harmonic distortion The total harmonic distortion. care should be exercised in assessing harmonic currents of frequencies other than the one for which the filter is tuned because they will also find a reduced impedance path Lower quality factor filters could be used in situations in which harmonic distortion barely exceeds the limits and a small filtering action is all that is needed to bring it into compliance.s. The best reduction of harmonic distortion will be achieved with large Q value filters. voltage at harmonic n. Vn is the single frequency r.) of the harmonics expressed as a percentage of the fundamental component. However. Current distortion levels can also be characterized by a THD value but it can be misleading when the fundamental load current is low. or THD. However. of a signal is a measurement of the harmonic distortion present and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency.m. Where. 6 elseif h==11 h=10. 7th and 11th harmonics.4 end xc=xfilter*(h^2)/(h^2-1). %present reactive power demand new_reactive_demand=load. To avoid such ambiguity a total demand distortion (TDD) factor is used instead. %the compensation from filter xfilter=(voltage.^2). clear all.frequency is high.5 elseif h==13 h=12.new_reactive_demand).*sin(acos(nwpowerf)). We are presently trying to simulate the filter on a single phase bus with the help of simpower toolbox of MATLAB software. The simulation involves calculation of total harmonic distortion of current and voltage with and without filter and FFT analysis of frequency response. %final reactive power reqcomp=(reactive_demand . close all.*1000/reqcomp. MATLAB Code : %single tuned filter design calculation clc. load= input('enter the load in KVA'). reactive_demand=load. %inductive reactance(ohms) 11 | P a g e . powerf= input('enter the power factor').7 elseif h==7 h=6.*sin(acos(powerf)). %xc is the capitance reactance(ohms) xl=xc/(h^2). defined as: WORK ALREADY DONE Till now we have designed a single tuned notch shunt passive filter for 5th . %filter impedance if h==5 %reduced harmonics for design tolerance h=4. nwpowerf= input('enter the desired power factor'). h=input('enter the harmonic present'). voltage= input('Enter the line volatage in kv'). As APF compensate the reactive power and cancel the harmonics. To mitigate the harmonics problem active power (APF) filters or active power line conditioners. The three main aspects of an active power conditioner are: The configuration of power converter (the topology of the filter) The control strategy (the calculation of APLC control reference signals) The control method used (how the power inverter follows the control reference) The main component in the APF is the control unit. The more usual configuration is a shunt APF to inject current harmonics into the point of common coupling (PCC). Figure 4 INTRODUCTION: To cancel the harmonics and compensate the reactive power APF is a viable solution. it avoids the propagation of current harmonics in the system. The APF can be installed in a low voltage power system to compensate one or more loads.14). The concept is to use an inverter to inject currents or voltages harmonic components to cancel the load harmonic components.c=1/(100*3. But the passive filters have several drawbacks like fixed compensation. 12 | P a g e .14*xc). xfund= abs(xl-xc). l=xl/(100*3. it is also called as active power line conditioners (APLC). large size and resonance problem. thus. %capacitance farad %inductance henry %impedance at fundamental frequency 50 hz Active filter To reduce the harmonics conventionally passive L–C filters were used and also capacitors were employed to improve the power factor of the ac loads. The control unit is mainly divided into two parts as follows. Current Modulator (Gate control signal): Current modulator is mainly used to provide the gate pulse to the active power filter (Inverter). Voltage source inverter (VSI) Current source inverter (CSI) The topology of active power filter is classified in to three types. hysteresis current controller etc. Series active power filters Shunt active power filters Hybrid active power filters(both active and passive filter) Finally based on the phases the APF is of mainly two types. and the number of phases. Controller(reference current generator and gating signal generator) 13 | P a g e . There are many techniques used for giving the gating signals to PWM VSI such as sinusoidal PWM. Here we have used sine multiplication theorem for active part of current calculation. here we have used adaptive hysteresis controller for the gate control signal. Two-wire (single phase) system. APF SYSTEM STUDIED: Single phase source A nonlinear load A voltage source PWM inverter. CONFIGURATION OF ACTIVE POWER FILTERS: APF’s can be classified based on converter type. Harmonic extraction technique Current modulator Harmonic Extraction: Harmonic extraction is the process in which. reference current is generated by using the distorted waveform. Three or four-wire three-phase system. triangular PWM. The converter type is mainly two types. topology. The integrator block is used to generate the fundamental active component of current Is* which is then subtracted with the load current to generate the reference current for the inverter. . REFERENCE CURRENT GENERATION The equations below describe the method of generation of reference current for the inverter. Let us suppose Il = load current Vs= source voltage ω= fundamental frequency (50hz) Load current can be written as : ∝ I L =∑ I n sin ( nωt +θn ) n=1 Multiplying both sides with sin (ωt) and integrating over a period of 2 π 2π ∫ I L sin ωt dωt 0 2π 2π ∫ I 1 sin ( ωt +θ1 ) sinωt d(ωt) = 0 2π ∝ + ∫ ∑ sin ( nωt +θn ) sin nωt d (ωt) 0 n=2 2π ∫ I L sin ωt d (ωt)=I1 ∫ sin2 ωt cos θ 1+ cos ωt sin ωt sin θ1 dωt 0 0 2π sin2 ωt cos θ1 dωt+¿ = 1 ∫ sin 2 ωt sin θ1 dωt 20 2π ∫¿ 0 I1 ¿ 14 | P a g e we get. It explains the working of the integrator block for generation of the reference current.Control strategy Figure 5 Figure 5 shows the basic block diagram of the control strategy being used here. The next part involves a adaptive hysteresis controller which compares the output of the inverter with the reference and orders the switching of inverters to minimize the error between them. such as uneven switching frequency that causes acoustic noise and difficulty in designing input filters. if the error current e(t) between the desired reference current iref(t) and the actual source current iactual(t) exceeds the upper hysteresis band limit (+h). thus the active power filter can improve the power factor by sending reactive power and thus the source current becomes in phase to the voltage phasor giving unity power factor. excellent dynamics and fastest control with minimum hardware. and measured line current of the APF is referred to as ‘i’. In the case of positive input current. There are various current control methods proposed for such active power filter configurations. Figure 6 ADAPTIVE HYSTERESIS CURRENT CONTROLLER In spite of several advantages. the basic hysteresis technique exhibits several undesirable features. The difference between i and iref is referred to as δ 15 | P a g e . I ¿s = I 1 cos θ1 sinωt = Active current I ¿F = I ¿s−I L gives the reference current to be generated by the inverter. ∝ = −I 1 sinθ 1 cosωt – ∑ I n sin(nωt +θ n) n=2 This reference current contains the reactive current and the harmonics present. The hysteresis band current controller is composed of a hysteresis around the reference line current. but in terms of quick current controllability and easy implementation hysteresis current control method has the highest rate among other current control methods.2π 1−cos 2 ωt dωt 2 = I 1 cos θ1 ∫ = I1 = cos θ 1 [2 π ] 2 I 1 cos θ1 π 0 Therefore gain of the integrator needed = 1 π The term when multiplied with sin (ωt) gives the active component of the load current at fundamental frequency. In equation the reference line current of APF is referred to as iref. Hysteresis band current controller has properties like robustness. Hysteresis current control loop The hysteresis band current controller for active power filter generates the switching pattern of the inverter. the upper switch of the inverter arm is become OFF and the lower switch is become ON. Figure 8 The above figure 8 shows the basic connection of the half bridge inverter to the line at point of common coupling using an inductor with suitably chosen value so as to have a linear rise in current. Using KVL in the circuit given in figure we can write V f ( t )−L d if =V s (t) dt d if 1 = ( V ( t ) −V s ( t ) ) dt L f 16 | P a g e .The switching logic for a half bridge VSI inverter is formulated as follows: If δ >HB upper switch is ON If δ <-HB upper switch is OFF Figure 7 Figure 7 shows the adaptive hysteresis band HB and –HB around the error and the switching pattern generated using the logic devised above. Figure 9 Using the geometry of the above figure 9 we can write the following −¿ arerising∧falling current due ¿ +¿∧I F the inductor equations where I ¿F V dc 2 +¿ .V s (t) ¿ .(2) dt L 2 ¿ From the figure ( ( 17 | P a g e ) ) .(1) iF 1 d = ¿ dt L ¿ −¿ if 1 −V dc d = −V s dt L 2 ¿ i−¿ −1 V dc d f = +V s . (3) .(4) Let f = .(6) .2HB = d i +¿ f ∗t dt 1 ¿ ¿ - d if ∗t dt 1 - d i ¿f ∗t dt 2 −¿ if d ∗t 2 dt ¿ 1 =switching frequency t 1 +t 2 i+¿ d i ¿f f d − dt dt ¿ ¿ −¿ Equation (3) + (4) = if d i ¿f d − dt dt ¿ ¿ ¿ −¿ if d t2 dt +¿ d i ¿f if (t 1+ t 2 ) = 0 d t 1 +¿ dt dt ¿ ¿ .i +¿ d f dt AC =tanα=¿ DC +¿ if d ∗t AC = dt 1 ¿ d i ¿f BC =tan β= DC dt ¿ d if BC = ∗t dt 1 AC – BC = AB = 2 HB = Similarly .(5) d Equation (3) – (4) = 4HB = From (5) 18 | P a g e i−¿ f t dt 2 i +¿ d f t 1−¿ dt ¿ ¿ ¿ - d if (t + t ) dt 2 1 =0 . Vdc . and the switching frequency of the inverter dt chosen. ( ) 19 | P a g e .−¿ i d f t2 dt d i ¿f +¿ = i dt d f t 1 +¿ dt ¿ Using (1) and (2) ¿ d if 1 V dc 1 V dc = −V s t 1− +V s t 2 dt f L 2 2 ¿ d if 1 1 V dc = t 1−t 2 )−V s ( t 1 +t 2 ) ( dt f L 2 [( ) ( ) [ ] ] 2−¿ t 1 t¿ ¿ ¿ Similarly in equation (6) d i ¿f 1 V dc 1 V dc 4HB = ( t 2 −t 1 ¿ −V s t 1+ +V s t 2+ L 2 L 2 dt ( 4HB = ) ( ) di 1 V −2 +V ( L +V )) L [ 2f V f ( dt ] ¿ f dc s s dc 4HB = [ ( ) [( ) ] ¿ −2 1 d i f +V s V dc f dt d if dt ¿ 2 d i¿ 2 2 L 1 V dc 4 V s L d i f 2V s L + − 2 − f L 2 f L V dc f dt L V dc f dt V dc f 2 [ ( ¿ + )] ] ¿ L V dc dif V s HB = − + 2 V dc f 8 Lf dt L This equation gives the instantaneous values of hysteresis band determined ¿ d if by the values of Vs . Logical circuit for S1 and S2 firing 20 | P a g e .Figure 10 Simulink model of the adaptive hysteresis model design. If going positive the error current is compared with upper hysteresis and while if going negative the error current is compared with the lower hysteresis band. Their difference gives the error current which is to be checked with the upper and lower hysteresis band. The output of both the comparator is fed to a SR flip flop. WORKING: The inputs taken are reference current I f* . So the error signal is passed through a differentiator to check the slope of error.Figure 11 The above logical circuit shows the implementation of switching circuit. filter current If and the adaptive hysteresis band generated instantaneously using the derived formula. 21 | P a g e . If the value of error is greater than the upper hysteresis band then S=1 R=0 thus Q=1 and hence upper switch of half bridge inverter S2 is OFF and Lower switch of half bridge inverter S1 is ON and vice versa. Power System Harmonics. 1985. D. 2001 2. P.REFERENCE 1. John Willey and Sons. 3. George J.Jodger. J. McGraw Hill P. Francisco C. Alexander Kusko. Power System Harmonics: fundamentals. CRC Press. 2007 4.Arrilaga.A. Springer VerlagPress. Performance for Passive and Active Power Filter in Reducing Harmonics in the Distribution System 22 | P a g e . Harmonics and Power Systems. Power Quality in Electrical Systems.Bradley. Marc T. and filter design .. De La Rosa.S. analysis.C.Wakileh. 2006 5.Thompson.
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