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  1. 1. Ramesh Babu P., Ashisa Dash, Smruti Ranjan Panda / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.180-185180 | P a g eElimination of Harmonics of Induction Furnace by ApplingPQ-Theory for the Control of Hybrid Selective Active FilterRamesh Babu P., Ashisa Dash, Smruti Ranjan PandaABSTRACTThis paper describes how to calculate thedifferent harmonic sequences that should befiltered with a hybrid selective active filter, fortwo control alternatives: load currentmeasurement or line current measurement. Theseresults are then generalized for hybrid selectiveactive filters. Passive parameters are chosenconsidering the resonances with the electricsystem that appear. Design basis are defined inorder to obtain a minimum cost filter which alsomeet the applicable regulations requirements.In this paper presents a hybrid selective activefilter configuration to mitigate harmonics, whichuses shunt passive and active filters. To obtain theswitching signals for the active filter have usedinstantaneous power theory proposed byH.Akagi. Hybrid selective active filter proposedscheme has been verified through varioussimulations in MATLAB-SIMULINKenvironment. Finally, results showing thepotentiality of the selective filter controlled forthe proposed methods are reported.Keywords - Induction furnace, Hybrid selectiveactive filter, pq –theory.I. INTRODUCTIONAn Induction furnace is an unbalanced,nonlinear and time varying load, which can causemany problems to the power system quality.Harmonics, inter-harmonics, voltage flicker &unbalance are the power quality problems which areintroduced to the power system as a result of non-linear and stochastic behaviour of the furnaceoperation [7]. The nonlinear voltage-currentcharacteristic of the arc can cause harmonic currentswhich when circulating by the net can produceharmonic voltages which can affect to other users [8].In the last decades, the evolution of two aspectsconcerning power systems has created conditionsfor a more extended use of active filters. A firstaspect is related to power semiconductor devicedevelopment. Converters capable of synthesizingvoltages and currents with an adequate bandwidthfor harmonic current compensation at MVA – levelsystems are now available at competitive prices. Theother aspect is the gradual application of regulationslimiting the generation of harmonic currents by thecustomers. Active filters are ideally suitable forfiltering localized harmonic currents in a guidedway , this allows to apply the concept ”you dirty, youclean”. This concept cannot be applied usingconventional passive filters. In the same way, activefilters allows to eliminate some of the problems ofpassive filters such as poor tuning due to dispersionof their characteristic parameters and resonances withthe impedance of the surrounding electrical networkwhich may appear.Among the different methods for controlling activefilters, the use of pq-theory (active and imaginarypower) [1], has demonstrated to be specially suitable.In particular, it has been used for separating theresidual harmonics and thus eliminating (as theoryindicates) or reducing (as it results in practice) theharmonic distortion. For the control of selectiveactive filters several works use the SRF method(Synchronous Reference Frame) [2] [3] [4] [5] [6]which is definitively a particular case of applying thepq- method with harmonic voltages as references.II. INDUCTION FURNACEOne of the most economic ways ofproducing steel is made through the use of inductionfurnaces. The problem with this kind of furnaces,from an electrical point of view, is the creation of aconsiderable harmonic distortion. The cause of thedistortion is within the induction furnace design andoperation. An induction furnace works melting thescrap using a medium frequency magnetic fieldcreated by a coil. The coil is fed by the mediumfrequency AC current supplied by an inverter whichis fed by a DC current converter connected to the ACdistribution network supply. As the created distortionis very high and affects the voltage supplied by thedistribution network, it is highly possible that otherloads supplied from the same network will beaffected. In this case, it is necessary to havecorrective actions in order to fulfil the legislationconcerning voltage harmonic distortion. Among thesecorrective actions, active filters are one of the mosteffective [12].2.1. SIMULINK MODEL OF THE INDUCTIONFURNACEAll the elements have been modeled usingexisting Simulink blocks contained in theSimPowerSystems block set. The distributiontransformers of the general services and the temperfurnaces consume 1800 kW with a cosφ of 0,85. Forsimulation purposes they have been modeled as a
  2. 2. Ramesh Babu P., Ashisa Dash, Smruti Ranjan Panda / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.181 | P a g elineal load of these characteristics. This is acceptableas their consumption is only a little portion of thetotal power consumed in the plant and they do notproduce any distortion. As there is no inductionfurnace electrical model in Simulink, new blockshave been created for the induction furnaces shownin fig.2.Fig.1.Equivalent circuit diagram of induction furnaceFig. 2.induction furnace without filterFig.3. induction furnace loadIII. PQ –THEORYIn 1983 Akagi et al.[13],[14] proposed anew theory for the control of active filters in three-phase power systems called “Generalized Theory ofThe Instantaneous Reactive power in Three phaseCircuits” or “ Theory of Instantaneous Real Powerand Imaginary Power” or “ Theory of InstantaneousActive power and Reactive power”, or “Theory of theinstantaneous power”, or simply as “p-q Theory”.Since p-q theory is based on the time domain. It isvalid both for steady-state and transient operation, aswell as for generic voltage and current wave forms,allowing the control of the active filters in real-time.Another advantage of this theory is simplicity ofits calculations, since only algebraic operations arerequired. The only exception is in the separation ofsome power components in their mean andalternating values. It is possible to exploit thesymmetries of the instantaneous power waveform foreach specific power system, achieving a calculationdelay that can be small as 1/6 and never greater than1 cycle of the power system frequency. It is alsoshown that calculations for reactive power and zero-sequence compensation do not introduce any delay.Furthermore, it is possible to associate physicalmeaning to the p-q theory power components, whicheases the understanding of the operation of any three-phase power system , balanced or unbalanced, withor without harmonics.3.1. THE P-Q THEORY APPLIED TO HYBRIDSELECTIVE ACTIVE FILTERS.The p-q theory is one of the several methods that canbe used in the control active filters [13],[15]. Itpresents some interesting features, namely:1-It is inherently a three-phase system theory.2-It can be applied to any three-phase systems(balanced or unbalanced, with or without harmonicsin both voltages and currents).3-It is based in instantaneous values, allowingexcellent dynamic response.4-It calculations are relatively simple (It onlyincludes algebraic expressions that can beimplemented using standard processors).
  3. 3. Ramesh Babu P., Ashisa Dash, Smruti Ranjan Panda / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.182 | P a g e5-It allows two control strategies: constantinstantaneous supply power and sinusoidal supplycurrent.To control the shunt active filter in such a way asto present zero impedance for the fundamental andpure resistance for the harmonics, the referenceoutput voltage of the shunt active filter is given byTransformation of the phase voltages ,, on the load side and source currents sui , svi ,swi into α-β orthogonal coordinates gives thefollowing expressions:(1)(2)According to [18], the instantaneous real power pand the instantaneous imaginary power q can bedefined as:(3)The dimension of q is not in watt, volt-ampere, orvar because . and . are defined bythe product of the instantaneous voltage in one phaseand the instantaneous voltage in one phase and theinstantaneous current in the other phase.The harmonic components Ph and qh are extractedfrom p and q by using a high pass filter. A first orderhigh pass filter, the cutoff frequency of which is 35hz, is used in the following experiment, filteringcharacteristics in the transient states being taken intoaccount. In the calculation circuit of shi the followingcalculations are performed.(4)Fig.4..Active power filter controllerWhere , A,B,C,and D are the Transfer functions. 232302121132A (5)LLLLVVVVB (6)232123210132C1 LLLLVVVV(7) 232302121132D (8)IV. SIMULATION AND PERFORMANCEINVESTIGATION OF ACTIVEFILTERIn this section the simulation analysis of Hybridselective active filter is described for InductionFurnace load and the FFT analysis has been carriedout simultaneously.
  4. 4. Ramesh Babu P., Ashisa Dash, Smruti Ranjan Panda / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.183 | P a g eFig.5.Induction furnace with filter circuit4.1. SIMULATED RESULTSFig 6.shows a set of simulated results of furnacecurrent, furnace voltage, three phase supply currentwith and without using filter. and the THD measuredfor all three phase line . The waveform of sourcecurrent is close to fundamental sinusoid, showing thatharmonic current is eliminated from the sourcecurrent. Therefore, it can be concluded that theproposed hybrid active filter can compensateharmonic current.Fig.6.(a).Furnace currentFig.6.(b).Furnace voltageFig.6.(c)Source current without filterFig.6.(d)Source current with filterFig.6.(e).THD of supply current Line-1 withoutfilter
  5. 5. Ramesh Babu P., Ashisa Dash, Smruti Ranjan Panda / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.184 | P a g eFig.6.(f).THD of supply current Line-2 without filterFig.6.(f).THD of supply current Line-3 without filterFig.6.(g).THD of supply current Line-1 with filterFig.6.(h).THD of supply current Line-2 with filterFig.6.(i).THD of supply current Line-3 with filterTHD’s of supply current before and afterfiltrationTable 1Supply current line no. BeforefiltrationAfterfiltrationTHD of supply currentLine-137.48% 2.02%THD of supply currentLine-234.29% 1.68%THD of supply currentLine-325.43% 1.00%CONCLUSIONA MATLAB based model of the hybrid activepower filter has been simulated for Induction furnaceload by Appling pq-theory for the control of hybridselective active filter. The simulation results showthat the supply current harmonics are compensatedvery effectively by using the hybrid selective activefilter.REFERENCES[1] H. Akagi, Y. Kanazawa, and A. Nabae,“Instantaneous reactive power compensatorcomprising switching devices withoutenergy storage components,” IEEE Trans.
  6. 6. Ramesh Babu P., Ashisa Dash, Smruti Ranjan Panda / International Journal of EngineeringResearch and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.185 | P a g eInd. Appl., vol. Vol. 20, no. 3, pp. 625–630,1984.[2] S. Bhattacharya, P. Cheng, and M. D. Divan,“Hybrid solutions for improving passivefilter performance in high powerapplications,” IEEE Transactions onIndustry Applications, vol. 33, no. 3, pp.732–747, 1997.[3] S.Bhattacharya and D. Divan, “Design andimplementation of a hybrid series activefilter system,” IEEE, pp. 189–195, June1995.[4] V.S. Ramsden D. Basic and P. Muttik,“Hybrid filter control system with adaptivefilters for selective elimination of harmonicsand interharmonics,” IEE Proc.-Electr.Power Appl., vol. 147, no. 3, pp. 295–303,May 2000.[5] S.Park J.H.Shung and K.Nam ,“New hybridparallel active filter configurationminimizing active filter size,” IEE Proc.Electr. Power Appl., vol. 147, no. 2, pp. 93–98, Mar. 2000.[6] P. Mattavelli, “A closed-loop selectiveharmonic compensation for active filters,”IEEE Transactions on Industry Applications,vol. 37, no. 1, pp. 81–89, 2001[7] M.A.Golkar, M.Tavakoli Bina and S.Meschi, “ A Novel Method of Electrical ArcFurnace Modeling for Flicker Study”[8] Swapnil Arya , Dr. Bhavesh Bhalja ,“Simulation of Steel Melting Furnace inMATLAB and its effect on power Qualityproblems” , National Conference on RecentTrends in Engineering & Technology, 13-14May 2011[9] M. A. Prieto, M. P. Donsión. "An ImprovedTime Domain Arc Furnace Model forHarmonic Analysis”, IEEE Trans on PowerDelivery, V.19, pp.367-373,2004[10] Labar Hocine, Dgeghader Yacine, KelaiaiaMounia Samira, and Bounaya Kamel”World Academy of Science, Engineeringand Technology 40 2008[11] Klaus Timm, Hamburg, basic Principals ofelectric furnaces, Edited by E. Plockingerand O. Etterich, John Wiley and Sons, Ltd,1985, pp 127- 160[12] G. Casaravilla, A. Salvia, C. Briozzo and E.Watanabe ,“Selective active filter applied toan arc furnace adjusted to harmonicemission limitations”, Latin America T&DIEEE Conference, San Pablo - Brasil, 2002[13] H.Akagi, Y.kanazawa, A. Nabae,“Generalized theory of the instantaneousreactive power in three phase circurits,”IPEC 83-int power electronics conf. Tokyo,Japan,1983, pp. 1375-1386.[14] H.Akagi, Y.kanazawa, A. Nabae,“Instantaneous reactive power compensatorcomprising switching devices withoutenergy storage components”, IEEE TransIndustry applic, vol.20, may /june 1984.[15] S-J. Huang and J-C Wu, “ A controlalgorithim for three-phase three-wired activepower filters under nonideal mainsvoltages,” IEEE Transcations on powerelectronics, vol, 14, no,4. Pp. 753-760, july1999.