PERFORMANCE OF SHUNT ACTIVE FILTER IN ALLELECTRIC SHIP (AES) A.CHAGHI A.GUETTAFI A. BENOUDJIT Laboratory L.S.PI.E Department of Electrcal Engneerng Faculty of Scences Engneerng Unversty of Batna Rue Chahd M d El Had Boukhlouf, 05000, Batna ALGERIA Tel: () 8 5, Fax: () 8 5 Abstract: The problem of harmonc power qualty, whch has ncreased lately on the contnental grd s expected to deterorate on shpboard nstallatons, too, after the advent of electrc propulson and other All Electrc shp (AES) schemes where the harmonc pollutant power electronc devces domnate. Ths work ams to nvestgate the applcaton of the emergng technologes of actve flters. It deals wth the desgn, analyss and smulaton of an actve power flter, capable to suppress the harmonc currents n the phases of an electrcal AES system, feedng nonlnear loads. The compensatng strategy uses a PWM source converter based on the generalsed nstantaneous power theory. A phase locked loop (PLL) s desgned to allow proper operaton under dstorted and unbalanced voltage. The smulatons results show the performance of the proposed shunt actve flter n All Electrc shp (AES) schemes. KeyWords: Harmoncs, power qualty, Actve power flter, Voltage Source Inverter, PLL. Introducton Durng the last years there has been a deteroraton to the problem of the harmonc dstorton, observed n voltage and current, n the electrcal plants of modern allelectrc shp [].The use of electrc propulson n marne applcatons provdes sgnfcant advantages over tradtonal mechancal solutons. Such supply networks are however, amongst the most demandng n term of power qualty and harmonc mtgaton due to the varaton n term of frequency and short crcut power. The problem s expected to deterorate n the future constructons due to the extensve use of devces wth power electroncs and perspectve of mplementng electrc propulson utlsng power pollutant converters feedng nnovatve A.C motors as mpled by all Electrc Shp (AES) concept. Evdently havng a good power qualty on electrc energy system of an AES should be the ultmate objectve, consderng ts mpact on all electrfed and electronc subsystems ncludng automaton and control ones. The electrc system of AES comprse a reduced number of generators and an ncreased number of nonlnear loads., whch nject nonsnusodal currents n the electrcal network and generates harmonc and reactve currents. The mpact of harmonc voltage and/ or current dstorton on electrc energy system cover a wde range of phenomena [],[]: Extra heatng losses n electrc machnery and cable wrng. Falure of equpment senstve to harmoncs. Exctaton of resonance phenomena resultng to sgnfcant overvoltage and /or overcurrents energy effcency and harmful to other applances. Conventonally, passve flters have been used to elmnate lne current harmoncs, but the performances of ths soluton s strongly dependent on the mans mpedance at the harmonc frequences [4]. To ensure passve flters do not enter nto resonance, t s usually necessary to nclude relatvely hgh levels resstve dampng n such applcatons gven the wde short crcut power and frequency varatons. Ths ncreases equpment losses whch s obvously undesrable n any applcaton but partcularly n marne context. In order to overcome these problems, the actve power flter relatvely wellresearched n recent years, s qute promsng approach for treatng the dsturbances on AES. In ths artcle an actve flter operatng n a current controlled mode s proposed. Moreover, we propose a PLL wth hgh performances and good results are obtaned when the man voltage are strongly unbalanced and contan harmoncs.
r s l s s (t) L (t) r c NonlnearLoad l c L d R d V s,, Supply nj R f, L f C dc V s,,,.. PLL V d,, Actve power Flter V dc I nj I s,, Harmonc Identfcaton I ref,, Control bloc Fg. Basc Scheme of Actve power flter Shunt actve power flter Fg. shows a power system wth a shunt actve flter and a nonlnear load. The actve flter uses an nverter and a frst order LType flter. The nverter s controlled n pulse wdth modulaton mode (PWM) wth the storage capactor as a voltage source. Dfferent methods for dsturbng current dentfcaton have been developed [5], [6]. The method usng nstantaneous power has been chosen n ths paper n order to compensate the current harmoncs. In ths method, as shown n Fg., the perturbng currents (harmonc, reactve and negatve components) are separated from the fundamental drect current component. Thus, a fundamental drect voltage reference s requred. If the network voltage reference s dsturbed, the non fundamental drect voltage components ntroduce an undesred nstantaneous power component. Consequently, the harmonc current reference wll be wrong. A three phase drect system at fundamental frequency s requred. Its magntude and phase shft can be of any value but a mnmum magntude voltage reference s requred for the storage capacty rechargng. Thus, we propose a PLL (Phase Locked Loop) n order to components) are separated from the fundamental drect current component. Thus, a fundamental drect voltage reference s requred. If the network voltage reference s dsturbed, the non fundamental drect voltage components ntroduce an undesred nstantaneous power component. Consequently, the harmonc current reference wll be wrong. A three phase drect system at fundamental frequency s requred. Its magntude and phase shft can be of any value but a mnmum magntude voltage reference s requred for the storage capacty rechargng. Thus, we propose a PLL (Phase Locked Loop) n order to extract the magntude and the phase of the drect fundamental voltage component out of the dsturbed voltage [7],[8]. Control strategy descrpton The generalsed theory of the nstantaneous power can be wrtten n the αβ0 coordnate system as: v sα =. vsβ 0 and the currents cα cβ =. 0 v v v s s s c c c () () The nstantaneous power components p, q and p 0 are expressed by:
v v α β α = q p and v v β α β Where: p = v () 0 0 0 p: Instantaneous real power q: Instantaneous magnary power p 0 : Instantaneous zero sequence power To calculate the reference compensaton currents n the αβ0 coordnates, the expresson () s nverted, and the powers to be compensated ( p p0 and q) are used: v v Cα α β p p 0 =. (4) * v v v v C q β α β β α where: p (t) :alternatve nstantaneous real power q (t) alternatve nstantaneous magnary power In order to obtan the reference current n the abc coordnates the nverse of the transformaton n expresson () s appled. c c c = 0 (5) By ths approach when appled to unbalanced load condton and snusodal current requred, the block dagram of fg. presents the procedure n ths cas c α c β 4 The PLL The phase voltages v a, v b and v c at load termnal are manly composed of postve sequence components, but can be unbalanced wth negatve and zero sequence components at fundamental frequency and can contan harmoncs. The detecton of the fundamental postve sequence component of v a, v b and v c s necessary f the shunt actve flter has to compensate load currents. The postve sequence detector uses a PLL (Phaselooked loop) crcut looked to the fundamental frequency of the system voltage. The desgn of the PLL should allow proper operaton under dstorted and unbalanced voltage waveform. The PLL crcut that s used s llustrated n Fgure..The PLL allows control of estmated phase angle θˆ wth respect to the angleθ of mans voltage.the PLL wll be looked out of the supply voltages when θ = ( θ θˆ) s equal zero. In ths case V = 0 and Vsq gves the RMS voltage. Moreover, we use a self tunng flter for extractng harmoncs. The self tunng flter allows to make nsensble the PLL to the dsturbances and flterng correctly n αβaxs [9]. Vs( θ ) Vs ( θ ) Vs( θ ) φ /φ (θ ) V α (θ ) V β Flter (θ ) V αf (θ ) V βf R V sd = 0 Sn Cos PI sd ωˆ s θˆ V d s s s v d C PLL v d v d θ d V s V s V s cα C cβ C Régulaton de la Vdc tenson contnue Vdcref vcα q p Régulateur p Pc q ( vs αvs) β ( vs αvs) β v sα v sα C Fg.. Current references dentfcaton * f * f * f Fg. The PLL crcut. 5 Smulaton results The effcency of the flter has been tested through the smulaton usng Matlab smulnk and power system blockset. The response of control strategy (and overall actve power flter) s studed by swtchng a non lnear load made up of a sx pulse thyrstor rectfer whch supples a 400 kva R d L d seres, wth the commutaton angle: α=0, under the followng parameters: Ac source 40V/50Hz, R s =.mω, L s =7.6µH, R c =4.mΩ, L c =68.67µH R d =0.8Ω, L d =.mh. L f =00µH et R f =5m Fgure.4 presents the network voltage nαβ axs as can be seen thevoltage are unbalanced and not snusodal. By the use of self tunng flter, they become snusodal, balanced and wthout phase
fgure.5.fg. 7 shows a number of selected smulaton results of utlty harmoncs compensaton whch have been realsed on the descrbed model. Correspondng spectrums before and after compensaton are gven n fg.8. The THD of the lne current source was 7.88% before compensaton s reduced nto.5% by the shunt actve power flter Fg.4 V α et V β Voltage of the network under unbalanced condtons Fg. 5 V α et V β Voltage of the network after fltrng Fg.7 b) Load and source current wave form, I LA : Load current, I f : compensaton current n phase A I s : lne current, Vdc: Capactor voltage Fg. 6 The synthetc sne and cosne generated by the PLL Fg. 7 c) Current spectrum after compensaton Fg. 7 a ) Current spectrum before compensaton
6 Concluson In ths paper, a shunt actve flter based on PWM voltage source nverter s proposed for compensatng current harmoncs, even under a dstorted voltage usng a PLL s detaled. The general model for the proposed scheme s obtaned and analysed usng nstantaneous power dentfcaton method.it has been shown that the lne current can be controlled to leads to a snusodal current n the ac source and consequently no voltage harmonc dstorton due to the nternal mpedance may occur. The valdty of the modellng, analyss and control method of the proposed shunt actve flter s proved by the computer smulaton. Smulaton results show that the shunt actve power flter s capable of compensatng the harmoncs generated by nonlnear load n dstrbuton system. In concluson, shunt actve power flter s feasble means power condtonng for marne power system, partcularly when appled to condton the low voltage AES shp servce secton of a marne electrcal system. [6] Y.Kamatsu, T.Kawabata «Acontrol Methode of Actve Power Flter In Unsymmetrcal Voltage System», EPE Sevlle, Septembre 995, Vol.. pp. 904 907. [7] V. Kaura, V. Blasko, "Operaton of a Phase Locked Loop System under dstorted Utlty Condtons", IEEE Trans. on Industry Applcatons, vol., N, January/February 997, pp. 586. [8] N. Bruyant, M. Machmoum «A generalzed study and control of shunt compensator for threephase threewre asymmetrcal systems», Electrmacs 99 ISBN, vol.iii, pp.886. [9] M;C. Ben habb, S. Saadate, An advanced approach control for four branch shunt actve power flter., EPEE 00Toulouse, France, pp. PP6 References: [] I.K. Hatzlau and al, Harmonc Power qualty on Naval Shps Electrc systems (Standards OvervewFeld Measurement ), Proceedng of rd Medterranean Conference and exhbton on Power Generaton Transmsson Dstrbuton and energy Converson (MEDPOWER 00), 46 November 00, Athens, Greece. [] R.Dugan, M. McGranaghan, H.W. Beaty, Electrcal Power system Qualty, McGraw hll, New York, 996. [] M. McGranaghan, Overvew of the Gude for applyng Harmonc lmts on Power Systems IEEE 59A, Proceedng of 8 th Internatonal Conference of Harmoncs and qualty Power, Atrhens(Greece), 68 october 998, pp.46469. [4] Nato AC/4(SG/6)SG/4 France paper 9/08(44)8 Sept.9, Harmonc polluton on Shp electrc sde crcutlmtaton of harmonc currents njected nto nsde crcut, DGA Note Technque n 5/9 SY/SEP, Pars 8 Sept.99. [5] H.Akag, Y.Kanazawa, A.Namba «Generalzed Theory of the Instantaneous Actve and Reactve Power In ThreePhase Crcuts», Proceedng of Internatonal Power Electroncs Conference (IPEC 000) ) Tokyo,, 98, pp. 7586.