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Application of Active Power Filter for Power Factor Correction of Nonlinear Loads


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Application of Active Power Filter for Power Factor Correction of Nonlinear Loads

Application of Active Power Filter for Power Factor Correction of Nonlinear Loads

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  • 1. IOSR Journal of Engineering (IOSRJEN)ISSN: 2250-3021 Volume 2, Issue 8 (August 2012), PP Application of Active Power Filter for Power Factor Correction of Nonlinear Loads D R Kirtane, P M Sonwane, B E Kushare Department of Electrical Engineering, K K Wagh Institute of Engineering, Pune University Nashik, Maharashtra, IndiaAbstract: - Reduction of harmonics is one of the major needs for an ideal power system and it is demanded thatit should ideally provide a balanced and pure sinusoidal voltage of constant amplitude to the loads. Loadsshould draw a current from the line at unity power factor .With the rapid development in power semiconductordevices, power electronics systems have matured and expanded to new and wide applications range fromresidential, commercial, aerospace to military and others. Power electronics interfaces, such as switchmodepower supplies (SMPS) are now clearly superior over the traditional linear power supplies resulting in moreand more interfaces switched into power systems. While the SMPSs are highly efficient, but because of theirnonlinear behaviour, they draw distorted current from the line, resulting in high total harmonic distortion (THD)and low power factor (PF). To achieve a smaller output voltage ripple, Practical SMPSs use a large electrolyticcapacitor in the output side of the single phase rectifier. Since the rectifier diodes conduct only when the linevoltage is higher than capacitor voltage, the power supply draws a high rms pulsating line current. As a resulthigh THD and PF are present in such power systems. Hence introduction of such devices in power systemneeded a solution for harmonic reduction and power factor correction.Keywords: - Nonlinear loads, Harmonic distortion, Power factor, Active power filter, Current compensation. I. INTRODUCTION The growing number of power electronicsbased equipment has produced an important impacton the quality of electric power supply. Both highpower industrial loads and domestic loads causeharmonics in the network voltages. At the same time,much of the equipment causing the disturbance is 2].quite sensitive to deviations from the ideal sinusoidalline voltage. Therefore, the power quality problem Fig. 1: Current Distortion Caused By Nonlinearmay originate in the system or may be caused by the Resistorconsumer itself. Some of the power equipmentscausing power quality problems are adjustable speed Nonlinear loads appear to be prime sourcesmotor drives (ASDs), electronic power supplies, of harmonic distortion in a power distribution current motor drives, battery chargers, Harmonic currents produced by nonlinear loads areelectronic ballasts. injected back into power distribution systems through These nonlinear loads draws highly distorted the point of common coupling (PCC). Thesecurrent from the source, which consists of harmonic, harmonic currents can interact adversely with a wideactive and reactive current components. Harmonic range of power system equipment most notablycan be defined as sinusoidal component of periodic capacitors, transformers, and motors causingwave or quantity having frequency that is integral additional losses, overheating and overloading [3].multiple of fundamental frequency. Harmonic For an increasing number of applicationsdistortion is caused by nonlinear devices in the power conventional equipment is proving insufficient forsystem. A nonlinear device is one in which the mitigation of power quality problems. Harmoniccurrent is not proportional to applied voltage. A distortion has traditionally been dealt with the use ofsimple circuit as shown in fig.1 illustrates the concept passive LC filters. However the application ofof current distortion. In this case, a sinusoidal voltage passive filters results in parallel resonances with theis applied to a simple nonlinear resistor in which the network impedance, over compensation of reactivevoltage and current vary according to the curve power at fundamental frequency, and poor flexibilityshown [1, for dynamic compensation of different harmonic frequency. The increased severity of power quality in power networks has attracted the attention of power engineers to develop dynamic and adjustable solutions to the power quality problems such 48 | P a g e
  • 2. Application of Active Power Filter for Power Factor Correction of Nonlinear Loadsequipments generally known as active filters, are also Where S1 is the apparent power is a measurecalled as active power line conditioners. They are of potential impact of load on the thermal capabilityable to compensate current and voltage harmonics, of the system. P1 defines how much active powermanage reactive power, regulate terminal voltage, being consumed while S1 defines capacity of thesuppress flicker, and improve voltage balance in system to deliver P1. Q is the reactive power that doesthree phase systems. The advantage of active filtering no real work and generally associated with theis that it automatically adapts to changes in the reactive elements. For example power appearingnetwork and load fluctuations. They can compensate across the inductance sloshes back and forth betweenfor several harmonic orders, and are not affected by the inductance itself and the power system sourcemajor changes in network characteristics, eliminating producing no network. For this reason it is known asthe rise of resonance between the filter and network reactive power since no power isimpedance. Another plus point is that they take up dissipated or expended. It is expressed in the units ofvery little space compared with traditional passive Vars.components [4]. The concept of power factor in sinusoidaland in nonsinusoidal type of load is discussed in II. B. Power factor in nonsinusoidal caseOperation of shunt power filter is given in III. In nonsinusoidal case the computation ofMethodology for power factor correction of nonlinear active power must include contributions from allload using single phase shunt active filter is given in harmonic components, thus it is the sum of activeIV. power at each harmonic. Reactive power consists of the sum of the traditional reactive power value at II. CONCEPT OF POWER FACTOR each frequency. D represents all the cross products of voltage and current at different frequencies. D is the Power factor is ratio of useful power to distortion power. Unit is volt ampere.perform real work i.e. active power to the powersupplied by utility i.e. apparent power.A. Power factor in sinusoidal case In nonsinusoidal case the power factor takes into account the contributions from all active power including both fundamental and harmonic frequencies known as True Power Factor. The true power factor is simply the ratio of total active power for all frequencies to the apparent power delivered by the utility. Fig. 2: Power Triangle in Sinusoidal Case Active power P is commonly referred to asthe average power or true power. It represents theuseful power expanded by loads to perform real worki.e. to convert electrical energy to another form ofenergy. In electric power real work is performed forthe portion of current that is in phase with the voltage. Fig. 3: Power Triangle in Nonsinusoidal CaseThe active power is the rate at which energy isexpanded, dissipated or consumed by the load. P can Assume that the main voltage is an idealbe computed by averaging the product of the sinusoidal voltage waveform , its rms value isinstantaneous voltage and current i.e. If the current has a periodic nonsinusoidal waveform, the Fourier transform can be applied This equation is valid for sinusoidal andnonsinusoidal conditions. For sinusoidal case there isonly one phase angle between voltage and current.Since only fundamental frequency is presenttherefore power factor is known as Displacement Where I0 is the DC component of the current.power factor. I1rmsthe fundamental component of the rms current and I2rms to Inrms the harmonics. For a pure AC signal I0= 0. The fundamental of the rms current has an 49 | P a g e
  • 3. Application of Active Power Filter for Power Factor Correction of Nonlinear Loadsinphase component I1rmsP and a quadrature component and subtracting it from a sinusoidal reference. TheI1rmsQ. So the rms current can be expressed as aim of shunt APF is to obtain a sinusoidal source current (is) using the relationship: is= iL- if . Then the real power is given by . As is the displacement anglebetween the input voltage and the inphase component Fig. 4: Principle Configuration of a VSI Based Shuntof the fundamental current APF Suppose the nonlinear load current can beAnd written as the sum of the fundamental current component (iL,f) and the current harmonics (iL,h) according to SThen power factor can be calculated as then the injected current by the shunt APF should be The resulting source current isOne can introduce the k factor by Which only contains the fundamental Where is the distortion angle. The k factor component of the nonlinear load current and thus freeis linked to the harmonic content of the current. If the from harmonics. Fig. 5 shows the ideal source currentharmonic content of is approaching to zero. when the shunt APF current completely cancels theK1. Finally Power Factor can be expressed by current harmonics from the nonlinear load, resultingP.F.= . Improving power factor means to in a harmonic free source current. From the nonlinearimprove both factors i.e. as 1; 1 reduce load current point of view, the shunt APF can bephase lag between I and V, and as 1; 1 regarded as a varying shunt impedance. Thereduce harmonic components of line current I which impedance is zero, or at least small, for the harmoniccan be achieved by means of active filtering frequencies and infinite in terms of the fundamentaleffectively [5]. frequency. As a result, reduction in the voltage Then the problem can be formulated as, to distortion occurs because the harmonic currentsdesign a single phase shunt active filter to drain flowing through the source impedance are reduced.harmonics and reactive component of a load current Shunt APFs have the advantage of carrying onlyto improve power quality of the electric grid. compensation current plus a small amount of active fundamental current supplied to compensate for III. SHUNT ACTIVE POWER FILTER system losses. It can also contribute to reactive power This is most important configuration and compensation. Moreover, it is also possible towidely used in active filtering applications. A shunt connect several shunt APFs in parallel to cater forAPF consists of controllable voltage or current source. higher currents, which makes this type of circuitThe voltage source inverter (VSI) based shunt APF is suitable for a wide range of power ratings [6].the most common type used today, due to its wellknown topology and straight forward installationprocedure. Fig. 4 shows the principle configuration ofa VSI based shunt APF. It consists of a DC buscapacitor (Cf), power electronics switches, andinterfacing inductors (Lf). Shunt APF acts as a currentsource, compensating the harmonic currents due tononlinear loads. The operation of shunt APF is basedon injection of compensating current which is Fig. 5: Shunt APF Harmonic Filtering Operationequivalent to the distorted current. This is achieved Principleby “shaping” the compensation current waveform (if),using the VSI switches. The shape of compensationcurrent is obtained by measuring the load current (iL) 50 | P a g e
  • 4. Application of Active Power Filter for Power Factor Correction of Nonlinear Loads IV. METHODOLOGY V. CONCLUSION The block diagram of the proposed system A block diagram is designed for powerof shunt active filter for power factor correction on factor correction of nonlinear load as a prototypenonlinear load is as shown in fig.6 model in this study. The compensation effectiveness The converter which is used as the active of an active power filter depends on its ability tofilter is a full bridge voltage source inverter using follow with a minimum error and time delay, theIGBTs (IRGP4PC3OUD), due to its current reference signal calculated to compensate thereversibility characteristics. The full bridge inverter is distorted load current. Hence decide control schemeconnected in parallel with AC mains through a filter for APF is the main task also deciding power circuitinductance LF and the DC side of the inverter is topology to give lossless and fast switching responseconnected to the capacitor CF. for compensation current is equally important. By appropriate control of the full bridgeswitches (IGBTs), the filter current cancels the REFERENCESharmonic component of the nonlinear loads, resulting [1] Rahul Virmani, Prerna Gaur, Himanshu Santosi, A.P.Mittal,in a sinusoid input current in phase with the AC main Bhim Singh, “Performance Comparison of UPQC and Active Power Filters For A Nonlinear Load ”, 978-1-4244-7781-voltage. 4110, IEEE 2010. The control block consists of two loops. The [2] Mikko Rautimo, Mika Salo, and Heikki Tuusa, “Comparisonouter voltage loop consists of comparison of voltage of Voltage source And Current source Shunt Active Poweracross DC bus i.e. electrolytic capacitor with a Filters”, IEEE Transaction on Power electronics,vol.22, No.22,March 2003.reference voltage. The resulting error is injected in an [3] Roger C. Dugan, “Electrical Power Quality”.2 nd ed.,Chap.5appropriate voltage controller. The output of voltage and 6,PP167-294, Tata McGraw Hill, Professionalcontroller is multiplied by a sinusoidal signal Engineering.proportional and inphase with the input voltage. The [4] J.G.Pinto, Pedro Neves, Ricardo Pregitzer, Luis F.C. Monteiro, Joao L.Afonso,“Single Phase Shunt Active Filterresult of this multiplication keeps the voltage across With Digital Control” POCTI/ESE 48242/2002.the DC bus capacitor constant. The inner current loop [5] L. Wuidart , Application note on “Understanding Powerconsists of the comparison of reference current Factor”, AN824/1003.obtained from band pass filter tuned at fundamental [6] Tan Perng Cheng , “A Single Phase Hybrid Active Power Filter with PhotoVoltaic Application”, PSZ 19:16 (Pind.frequency and the line current. The resulting error is 1/97).injected in an appropriate current controller which [7] P. M. Sonwane, B.E. Kushare, “Capacitor Placement forconsists of PI controller. The output of this controller Loss Reduction in 132 kV Raymond Substation Usingis compared with a triangular signal, generating the DigSilent”, NPATS Nashik,, December 2/3, signals to the switches. The control strategy ofthe active power filter allows the compensation of theharmonics and phase displacement of the inputcurrent for the nonlinear load . Fig.6: Block Diagram for P.F. Improvement using Shunt APF 51 | P a g e