SANDIA FREQUENCY SHIFT BASED ARTIFICIAL IMMUNE SYSTEM FOR ANTI- ISLANDING DETECTION

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1 Intrnational Journal of Tchnical Rsarch and Applications -ISSN: , Volum 3, Issu4 (July-August 215), PP SANDIA FREQUENCY SHIFT BASED ARTIFICIAL IMMUNE SYSTEM FOR ANTI- ISLANDING DETECTION A.Y.Hatata 1, El-H.Abd-Raboh 2 Bishoy.E.Sdhom 3 Faculty of nginring, Mansoura Univrsity, Egypt ng_bishoy9@yahoo.com Abstract This papr prsnts a nw mthod for islanding dtction. Th proposd mthod dpnds on applying an artificial intllignc mthod basd artificial immun systm (AIS) with sandia frquncy shift (SFS) mthod. AIS is usd to improv th prformanc of th SFS mthod including th improvmnt of th systm powr quality, rduction in non-dtction zon (NDZ) and rducing th islanding dtction tim. Th proposd mthod is tstd and applid to a tst systm and th rsults show that th proposd mthod is mor fficint in islanding dtction. Indx Trms Anti-islanding Dtction, Sandia Frquncy Shift (SFS), Non Dtction Zon (NDZ), Total Harmonic Distortion (THD), Artificial Immun Systm (AIS), Clonal Slction Algorithm. I. INTRODUCTION Distributd gnrations (DG) ar small-scal gnration units that can b installd nar to consumrs with th ability of intracting with th grid importing or xporting nrgy. On of th major problms associatd with such gnrators is th unwantd islanding phnomnon. Islanding occurs whn a portion of th distribution systm bcoms lctrically isolatd from th rmaindr of th powr systm yt continus to b nrgizd by on or mor DGs. An important rquirmnt to intrconnct a DG to a powr distributd systm is th capability of th DG unit to dtct islanding with th minimum tim possibl. Th continud nrgizing of th load can lad to damag of quipmnt or injury to maintnanc prsonnl working within th islandd sction without knowing th systm is still aliv. Most DG units ar dsignd in such a way that thy will disconnct from th grid whn ovr/undr voltag or frquncy occurs on th ntwork. In th cas that th grid is disconnctd whil th load and th sourc ar matchd, th DG units will thus continu to powr th lin, thrby lading to th formation of an island. DGs must dtct islanding and immdiatly stop fding th utility lins with powr. This is known as anti-islanding. Anti-islanding mthods assist th DG units to dtct islanding or forc th islandd sction out of th normal oprational spcifications of th grid. This is achivd by attmpting to prturb ithr th voltag or th frquncy of th ntwork. In th prsnc of th grid, ths prturbations will hav no ffct on th voltag or frquncy. If th grid is disconnctd, though, variations in voltag or frquncy can occur. Ths variations can b dtctd by th ovr/undr voltag or frquncy protction systm, and th DG is disconnctd or shutdown. Anti-islanding mthods gnrally can b classifid into four major groups, which includ passiv mthods, activ mthods, hybrid mthods and communication bas mthods [1]. Passiv mthods monitor slctd paramtrs, such as voltag, frquncy or thir charactristics, and thy switch off th invrtr if on of ths paramtrs dviats outsid spcifid boundaris or conditions [2].Th boundary limits of ths paramtrs dfin th non-dtction zon (NDZ). Th passiv mthods includ: Ovr/Undr Voltag Protction (OVP/UVP), Ovr/Undr Frquncy Protction (OFP/UFP), voltag phas jump dtction, and dtction of voltag and currnt harmonics mthods [3-4]. Ths mthods ar concptually simpl and asy to implmnt and do not introduc any chang to th powr quality of th systm. Howvr, thy hav a numbr of waknsss including th inability to dtct islanding bcaus thy hav a larg NDZ. Thy tnd to fals trip du to disturbancs on th grid which may wakn grid stability and scurity. In ordr to rduc th NDZ, particularly in cass whr th local loads ar clos in capacity to th DG systms; activ dtction mthods hav bn proposd. Activ mthods prturb th connctd circuit and thn monitor th rspons to dtrmin if islanding has occurrd [5-8]. Activ mthods includ: Impdanc masurmnt mthod [9-11],Slip Mod Frquncy Shift (SMS) [12], Activ Frquncy Drift (AFD) [13-19], Sandia Frquncy Shift (SFS) [13, 2-22], Sandia Voltag Shift (SVS)[5, 8], Ractiv Powr Variation (RPV) mthod [23], and Mains monitoring units with allocatd allpol switching dvics connctd in sris (MSD) [24]. Activ mthods attmpt to crat a powr mismatch btwn th load and th DG whn thy ar closly matchd. It is possibl that som of th activ mthods can cancl out th mismatch in an attmpt to crat on. It should also b notd that th positiv fdback in som activ mthods could lad to powr-quality dgradation [25]. Th injction signals can also induc som voltag wavform distortion. 355 P a g

2 Intrnational Journal of Tchnical Rsarch and Applications -ISSN: , Volum 3, Issu4 (July-August 215), PP Among frquncy drift islanding dtction mthods, Sandia Frquncy Shift (SFS) is considrd as on of th most ffctiv mthods in dtcting islanding conditions. Th mthod can b usd to improv th NDZ and THD by using a positiv fdback gain, but still affct th powr quality of th systm. This papr prsnts a proposd tchniqu to modify SFS anti-islanding mthod using Artificial Immun Systms (AIS). Th mthod optimizs th paramtrs of th SFS mthod to rduc both th NDZ and th THD of th currnt wavforms. AIS ar computational paradigms that blong to th computational intllignc family and ar inspird by th biological immun systm. During th past dcad, thy hav attractd a lot of intrst from rsarchrs aiming to dvlop immun-basd modls and tchniqus to solv complx computational or nginring problms. Th impact of th load paramtrs on th prformanc of th SFS mthod hav bn discussd in many paprs [2, 21, 22, 27, 28, and 29]. Howvr ths paprs concrnd with rducing NDZ only and don't tak into considration th powr quality dtrioration. In [19] th prformancs of SFS mthod and its major factors affcting th phas-frquncy charactristic of th islanding systm wr analyzd. Authors in [26] prsntd a passiv mthod of dtcting islanding of DG inspird by th information procssing proprtis of natural immun systm. Th rmaindr of this papr is organizd as follows; Sction 2 dscribs th SFS anti-islanding mthod, Sction 3 introducs th problm formulation, Sction 4 prsnts th modifid SFS basd AIS mthod and th AIS algorithm for solving this problm, Sction 5 dscribs th systm modling and simulation, and Sction 6 prsnts th rsults and discussion. Finally, Sction 7 concluds th papr. II. SANDIA FREQUENCY SHIFT ANTI-ISLANDING METHOD Sandia Frquncy Shift (SFS) is on of th activ islanding dtction mthods that rly on frquncy drift to dtct an islanding condition. Ths mthods dpnd on injcting a distortd currnt wavform into th original rfrnc currnt of th invrtr, thrfor in th cas of islanding opration th frquncy drift up or down dpnding on th sign of th so calld chopping factor "C f". A positiv fdback is utilizd to prvnt islanding and to dcras NDZ valu. Th procdurs of applying th SFS mthod can b summarizd as follow [24]: 1- Injct a currnt harmonic signal with a limitd duration into th Point of Common Coupling (PCC) so as to comply with th maximum total harmonic currnt distortion (THD i) allowd by intrconnction standards. 2- Th injctd currnt signal distorts th invrtr currnt by prsnting a A sgmnt for drift up opration as shown in Fig. 1. Fig. 1 SFS currnt rfrnc of PV invrtr 3- Th dsirabl ffct of th A sgmnt, is that th fundamntal componnt of th invrtr currnt lads th voltag by a small angl, which is frquncy dpndnt and it crats a positiv fdback. 4- Whn th grid is disconnctd, th frquncy of th voltag of th PCC tnds to drift, raching valus highr until th frquncy out of th OFP/UFP trip window (Rang) and th invrtr is disconnctd. 5- A positiv fdback is utilizd to prvnt islanding. Th non-dtction zon (NDZ) of th SFS highly dpnds on its dsign paramtrs. Th dsign paramtrs includ both chopping factor C f and fdback gain factor K. If ths paramtrs ar not proprly tund, it may rsult in failur of th mthod or dtrioration of th systm powr quality through injction of high amount of harmonics. Howvr, SFS may fail to dtct islanding considring a fact that th dviations of voltag and frquncy ar small du to th powr balanc btwn DG sourcs and local loads. Th chopping factor is a function of th rror in th lin frquncy and may b computd as: (1) Whr is th chopping factor whn thr is no frquncy rror, K is an acclrating gain that dos not chang dirction, f a is th lin frquncy masurd at PCC, and f lin, is th nominal lin frquncy. III. SFS PARAMETER OPTIMIZATION Th two paramtrs and hav diffrnt ffct on th NDZ of SFS schms. Initial chopping factor changs th location of NDZ on load spac, but it dosn't chang th siz of NDZ. Incrasing caus s advrs impact on powr quality, as it prturb th ntwork with a distortd currnt. Th total harmonic distortion (THD) of th output currnt is dirctly proportional to [13]. According to th impact on powr quality; smallr valus ar prfrrd in stting. Positiv fdback gain K has a positiv impact on NDZ considration. Incrasing will dcras NDZ and push th 356 P a g

3 Intrnational Journal of Tchnical Rsarch and Applications -ISSN: , Volum 3, Issu4 (July-August 215), PP NDZ towards load spac with highr, but it may also produc ngativ impact on powr quality of th distribution systm. Thrfor smallr valus of paramtr ar prfrrd for fficint dtction of islanding. To minimiz both NDZ and THD to accptabl limit, it is ncssary to optimiz th valus of and K. In this papr AIS optimization tchniqu is usd to obtain optimal valus of and K. A. Objctiv function Th objctiv function is to minimiz variabl paramtrs of th SFS, which can b xprssd mathmatically as: Min ( ) = (2) whr is th maximum valu of load rsonant frquncy that will rsult in islanding opration, is th minimum valu of load rsonant frquncy that will rsult in islanding opration, and thy can b xprssd as [31]: (3) (4) is th phas angl of th invrtr and can b computd as: (5) B. Problm Constraints Total harmonic distortion limits and acclrating gain limit ar th main constraints for which th objctiv function in (2) is subjctd: i. Total harmonic distortion limits Du to its ngativ impact on th powr quality of th distribution systm; THD must b limitd to a prst valu. According to IEEE Std limits THD must b lssr than 5% [3]. ii. Acclrating gain limit Th prformanc of th SFS is affctd by th positiv gain cofficint K. Bttr prformanc is achivd with largr valus of K. Manwhil incrasing K will incras th currnt distortion and rsults in bad ffct on systm powr quality. Th problm is solvd using AIS to obtain th optimal valus of both and K that minimiz th NDZ and THD to accptabl valus in a short tim. IV. MODIFIED SFS BASED AIS METHOD Th immun systm of vrtbrats including human is composd of clls, molculs and organs in th body which protct th body against infctious disass causd by forign pathogns such as viruss, bactria. To prform ths functions, th immun systm has to b abl to distinguish btwn th body s own clls such as slf clls and forign pathogns such as non-slf clls or antigns. Aftr distinguishing btwn slf and non-slf clls, th immun systm has to prform an immun rspons in ordr to liminat non-slf cll or antign. Clonal slction thory xplains how th immun systm fights against an antign. It stablishs th ida that only thos clls which rcogniz th antign, ar slctd to prolifrat. Th slctd clls ar subjctd to an affinity maturation procss which improvs thir affinity to th slctd antigns [32, 33]. AIS mimics ths biological principls of clon gnration, prolifration and maturation. Th fundamntal of AIS is inspird by th thortical immun systm and th obsrvd immun functions, principls, and modls [34, 35]. Today, th AIS tchniqus ar usd to solv complx problms in many aras that includ nginring, scinc, computing, and othr rsarch aras. Th following stps summariz th procdur of applying SFS basd AIS mthod to solv th islanding dtction problm using SFS tchniqu. A. Antibody rprsntation In applying AIS to solv a problm; th solution of th problm is considrd as a population of antibodis. In this study both C fo and K ar considrd as antibody and ach paramtr is rprsntd by a gn of antibody. B. Initialization Th first stp of applying th AIS mthod is th gnration of initial population. Th initial population is gnratd btwn a pr-dfind minimum and maximum valus using a random function. If th gnratd solutions do not fall into th fasibl rang, thy ar ignord and th gnration procss is rpatd until th rquird numbr of solutions is gnratd. Th siz of th initial population is dtrmind by making a trad-off btwn quality of a solution and computation tim to yild that solution. C. Affinity function To introduc affinity (fitnss) function, th variabls should b put in th modl and thn th diffrnc of th stimatd valus from th actual data for ach antibody is calculatd and in ach gnration th individual with minimum diffrnc must b rturnd. Individual paramtrs ar slctd randomly and th affinity is calculatd according to Euclidan distanc [36]: (6) D. Slction In slction stp, n antibodis with highst affinity ar slctd to gnrat a nw population. E. Cloning Th slctd n individuals of th population that ar clond (rproducd) by th clonal procss, giving ris to a tmporary population of clons, C. Th highr th affinity, th largr th numbr of clons gnratd for ach of th n slctd 357 P a g

4 Intrnational Journal of Tchnical Rsarch and Applications -ISSN: , Volum 3, Issu4 (July-August 215), PP antibodis. Antibodis in th population must b clond according to thir affinity and gnrat a tmporary population. F. Mutation Th clond antibodis ar mutatd to crat a population T. During mutation, it assigns a lowr mutation rat for highr affinity antibodis than low affinity antibodis. Th ida is that th antibodis clos to a local optimum nd only b fintund, whras antibodis far from an optimum should mov largr stps towards an optimum or othr rgions of th affinity landscap. G. Rslction and divrsification This procss rslcts th improvd antibodis from th population T to updat it. Finally, th divrsity introduction procss rplacs th low affinity antibodis with nw ons. A flowchart of th modifid SFS basd AIS mthod is shown Ra d Crat initial antibody ( K and ) Fo ac antibod simulat th modl and calculat th function r h NDZ y and gt th valu of F objctiv,thd and islanding dtction tim t Sl ct th Star t K (. :1 ) Cf (. :. ) fmi fma 1, o syst 1 5 dat, n, x, m a nx antibod t y Calculat th rror distributi on in Fig. 2. Fig. 2 Flowchart of th modifid SFS basd AIS mthod H. Systm modling and simulation To vrify th proposd mthod and prov its ffctivnss, it is applid to a tst systm shown in Fig. 3. Th systm consists of a PV array, connctd to th grid PCC through a currnt controlld VSI invrtr to supply a local ac load. Th load can also b supplid by th grid through a powr transformr. Th local load is rprsntd by a paralll RLC with variabl rsonant frquncy and quality factor. Th utility brakr conncts th grid to th PCC in cas of normal opration. For islanding condition th brakr is opnd at a prscribd tim. Th tst systm is modld and simulatd in MATLAB/Simulink nvironmnt. Th simulation paramtrs ar prsntd in Tabl (1). Th simulation is implmntd in th following stps: Th frquncy is firstly masurd. If th frquncy xcds th IEEE. Std limits, thn th OFP/UFP will gnrat a fault signal to shutdown th invrtr. In cas that load and DG output ar closly mismatchd, thn th frquncy of th ntwork is prturbd to crat a powr mismatch btwn load and DG. A variations in frquncy can b dtctd by OFP/UFP systm and consquntly th DG is disconnctd or shutdown. Sinc this prturbation signal may induc currnt and voltag wavform distortion, th load currnt is chckd to nsur that th THD limits ar not violatd. Calcula t th affinit y of antibodis Simula distributi t syst on wit bs m paramtt h rs Clon slction Mutat th Y s clon Rach siz populati of on Y s Conditio ar ns satisfid N o (by slct numbr antibodis hav high that ) affinity populati accordin t on valu g o N o th affinit y Fig. 3 Block diagram of th tst systm Tabl 1: Simulation paramtrs Grid voltag (rms) Grid frquncy LC filtr PV systm output powr 4 V 5 Hz L = 18 mh C = 3 μf P inv = 3 kw Q inv = Var Gnra t n an w d antibodi usin th ol antibodi Savs th bsg paramt d s t rs 358 P a g

5 Intrnational Journal of Tchnical Rsarch and Applications -ISSN: , Volum 3, Issu4 (July-August 215), PP Paralll RLC load R = 12Ω L = 153mH C = 67μF 3 2 Load Currnt V. RESULTS AND DISCUSSION In this study th grid-connctd currnt controlld invrtr fd by a DC voltag sourc is disconnctd aftr.228 sc. Both th convntional SFS and th proposd modifid SFS basd AIS mthods ar applid to th tst systm and a comparison btwn th rsults is prsntd blow. A. SFS mthod Th convntional SFS mthod is applid to th tst systm shown in Figur 3. Th simulation rsults show that: th fdback gain K quals to.96 and quals to.26 with a NDZ of and THD of 4.43%. Fig. 4 illustrats th systm rspons for dtcting th islanding condition. Th islanding is dtctd at.2372 sc. so that th DG is disconnctd 9.2 ms aftr th grid disconnction (which occurs at.228 sc). Fig. 5 shows th voltag and load currnt wavforms during th simulation priod, whras Fig. 6 shows th frquncy chang aftr th grid disconnction. Islanding Dtction Tim (sconds) Islanding Dtction Tim Tim (sconds) Fig. 4 Systm rsponss to dtct island condition Vpcc (Volts) Voltag at PCC Vpcc Vpcc Islanding dtction I load (Ampr) Tim (sconds) b) Load currnt Fig. 5 Voltag and load currnt during simulation tim Frquncy (Hz) Systm frquncy Tim (sconds) Fig. 6 Frquncy changs during th simulation priod B. Modifid SFS basd AIS mthod In this cas th modifid SFS-basd AIS mthod is applid to th studid systm. Fig. 8 shows population and cloning of th bst affinity valus. Th optimal valus of th fdback gain K and ar.18 and.36 rspctivly, with a NDZ of and THD of 3.91%. Fig. 9 illustrats th systm rspons for dtcting th islanding condition. Th islanding is dtctd at sc so that th DG is disconnctd 1.28 ms aftr th grid disconnction. Fig.1 shows th voltag and load currnt wavforms during th simulation priod, whras Fig. 11 shows th frquncy chang aftr th grid disconnction Islanding dtction at.2372 s NDZ Tim (sconds) a) Voltag at PCC K Fig. 8 Population and cloning of th bst affinity valus Cfo 359 P a g

6 Intrnational Journal of Tchnical Rsarch and Applications -ISSN: , Volum 3, Issu4 (July-August 215), PP Islanding Dtction Tim(Sconds) Islanding Dtction Tim Tim (sconds) Fig. 9 Systm rsponss to dtct island condition Vpcc (Volts) Voltag at PCC Tim(sconds) Load Currnt Vpcc islanding dtction at s (a) Voltag at PCC aftr applying AIS I load (Ampr) Vpcc islanding dtction Tim (sconds) (b) Load currnt aftr applying AIS Fig. 1 Voltag and load currnt during simulation tim aftr applying AIS Frquncy (Hz) Systm Frquncy Tim (sconds) Fig. 11 Frquncy changs during th simulation priod VI. RESULT ANALYSIS Th rsults show that convntional SFS has THD of 4.43% and th DG is disconnctd 9.2 ms aftr th grid disconnction. In cas of applying th modifid SFS mthod th THD is 3.91% and th DG is disconnctd aftr 1.28 ms from th grid disconnction. Th proposd mthod dcrass th tim of islanding dtction to just 13.9% of that attaind by th convntional mthod. At th sam tim th proposd mthod dcrass th THD to 88.26% of th THD obtaind by th convntional mthod. It also rducs th NDZ. Th rsults prov th fficincy and spd of th proposd mthod in islanding dtction. VII. CONCLUSION This papr prsnts a proposd tchniqu to modify SFS anti-islanding mthod using Artificial Immun Systms (AIS). Th mthod optimizs th paramtrs of th SFS mthod to rduc both th NDZ and th THD of th currnt wavforms. A singl-phas grid-tid photovoltaic distributd gnration systm was usd to vrify th mthod. A comparison btwn th proposd mthod and convntional SFS was prsntd and th rsults show that th proposd mthod gnrats lss THD than th convntional SFS, which rsults in fastr islanding dtction and bttr non-dtction zon. Th dducd optimizd paramtr stting hlps to achiv th "non-islanding invrtr" as wll as last potntial advrs impact on powr quality. REFERENCES [1] W. Toh, C. Tan, An Ovrviw of Islanding Dtction Mthods in Photovoltaic Systms, World Acadmy of Scinc, Enginring and Tchnology Vol. 5, 211. [2] K. Tunlasakun, K. Kirtikara, S. Thpa, V. Monyakul, A microcontrollr basd islanding dtction for grid connctd invrtr Th 47thIEEE Midwst Symposium on Circuits and Systms, X/4 24 IEEE. [3] A.Timbus, A.Oudalov and Carl N.M. Ho, Islanding dtction in smart grids, Enrgy Convrsion Congrss and Exposition (ECCE),pp , 21 IEEE. [4] M. Hanif, M. Basu and K. Gaughan, A Discussion of Anti-islanding Protction Schms Incorporatd in a Invrtr Basd DG,Intrnational Confrnc on Environmnt and Elctrical Enginring (EEEIC), 1th Intrnational, 8-11 May 211. [5] D. Vlasco, C. Trujillo, G. Garcrá and E. Figurs,"Rviw of Anti-Islanding Tchniqus in Distributd Gnrators",Rnwabl and Sustainabl Enrgy Rviws,14 (21) [6] M.Robitaill, K.Agbossou, M.Doumbia, and R.Simard, Islanding Dtction Mthod for a Hybrid Rnwabl Enrgy Systm, Intrnational Journal of Rnwabl Enrgy Rsarch, IJRER, Vol.1, No.1, pp.41-53, 211. [7] M. Laour, A. Mahran,F. Akl, M.Chikh and D. Bndib, Implmntation of Activ Anti-islanding Mthods Protction Dvics for Grid Connctd Photovoltaic Systms, 6thIntrnational Confrnc on Computr and Elctrical Enginring (ICCEE 213)Octobr 12-13, 213, Paris, Franc. 36 P a g

7 Intrnational Journal of Tchnical Rsarch and Applications -ISSN: , Volum 3, Issu4 (July-August 215), PP [8] B. A lvarz, O. Rivra,"Survy of distributd gnration islandingdtction mthods". Latin Amrica Transactions, IEEE (Rvista IEEE Amrica Latina), Vol:8, No:5,pp , 21. [9] P. Mahat, B. Bak-Jnsn, "Rviw of Islanding Dtction Mthods for Distributd Gnration",Third intrnational confrnc on lctric utility drgulation and rstructuring and powr tchnologis, 28, DRPT April, 28. p [1] P. Mahat,Z. Chn, B. Bak-jnsn, "Rviw on Islanding Opration of Distribution Systm with Distributd Gnration", Powr and nrgy socity gnral mting,pp.1 8, 211 IEEE. [11] M. Roop, J. Ginn, J. Stvns, W. Bowr, S. Gonzals, "Simulation and ExprimntalStudy of thimpdanc Dtction Anti-Islanding Mthod in thsingl Invrtr Cas".Photovoltaic Enrgy Convrsion, Confrnc Rcord of th 26 IEEE 4th World Confrnc on, Volum 2, pags: , May 26. [12] F. Liu, Y. Kang, Y. Zhang, S. Duan, X. Lin "Improvd SMS Islanding Dtction Mthod for Grid- Connctd Convrtrs", Rnwabl Powr Gnration, IET (Vol:4, No: 1,pp , January 21. [13] F. Liu, Y. Kang and S. Duan, "Analysis and Optimization of Activ Frquncy Drift Islanding DtctionMthod" Applid Powr Elctronics Confrnc, APEC 27-Twnty Scond Annual IEEE, pags: , Fb. 25, 27-March 1, 27. [14] Z. Y, A. Kolwalkar, Y. Zhang, P. Du and R. Walling, "Evaluation of anti-islanding schms basd on nondtction zon concpt," IEEE Transactions on Powr Elctronics, Vol 19, No 5, pp , Sptmbr 24. [15] L. PhaniRaghav, T. Sandhya, An Activ Frquncy Drift Mthod for an Islanding Dtction of Grid Connctd Microturbin Gnration Systm, Intrnational Journal of Innovativ Rsarch in Scinc, Enginring and Tchnology- (ICETS 14), Vol 3, Spcial Issu 1, Fbruary 214. [16] A.Yafaoui, B. Wu, and S.Kouro, Improvd Activ Frquncy Drift Anti-islanding Dtction Mthod for Grid Connctd Photovoltaic Systms, IEEE Transaction on Powr Elctronics,, Vol. 27, No. 5, May 212. [17] L. Lops, and Y. Zhang, Islanding Dtction Assssmnt of Multi-invrtr Systms with Activ Frquncy Drifting Mthods IEEE Transaction on Powr Dlivry,Vol. 23, No. 1, January 28. [18] A. Yafaoui, B. Wu and S.Kouro, Improvd Activ Frquncy Drift Anti-islanding Mthod with Lowr Total Harmonic Distortion,IECON 21-36th Annual Confrnc on IEEE Industrial Elctronics Socity,pp , 21IEEE. [19] W. Huang,T. Zhng,F. Yuan,Z. Wang,S. Xu, Analysis of th NDZ Formulation Thory of Activ Frquncy Shift Islanding Dtction Mthod for Grid Connctd PV Systm, IEEEPowr and Enrgy Enginring Confrnc (APPEEC), PES Asia-Pacific,pp. 1 5, 213. [2] H. Vahdi, and M.Karrari, Adaptiv Fuzzy Sandia Frquncy Shift Mthod for Islanding Protction of Invrtr Basd Distributd Gnration,IEEE Transaction on Powr Dlivry, Vol. 28, No. 1, January 213. [21] P.Du, Z. Y, E. Apont, J. Kith, and L. Fan, Positiv-Fdback-Basd Activ Anti-IslandingSchms for Invrtr-Basd Distributd Gnrators:Basic Principl, Dsign Guidlin andprformanc Analysis, IEEE Transaction on Powr Elctronics, vol. 25, no. 12, pp , Dc. 21. [22] X. Wang, W. Fritas, and W. Xu, Dynamic Non- Dtction Zons of PositivFdback Anti-Islanding Mthods forinvrtr-basd Distributd Gnrators IEEE Transaction on Powr Dlivry,Vol. 26, No. 2, pp April 211 [23] Y. Jung, J. So, G. Yu, J. Cho, Modling and Analysis of Activ Islanding Dtction Mthods for Photovoltaic Powr Conditioning Systms, Elctrical and Computr Enginring, Canadian Confrnc(CCECE),Vol:2, 24 IEEE. [24] W. Bowr and M.Ropp, Evaluation of Islanding Dtction Mthods for Photovoltaic Utility-Intractiv Powr Systms",Intrnational Enrgy Agncy, Rport IEA PVPST5-9, 22. [25] P. Ray, N. Kishor, and S.Mohanty, Islanding and Powr Quality Disturbanc Dtctionin Grid-Connctd Hybrid Powr Systm UsingWavlt and S Transform IEEE Transactions on Smart Grid,Vol. 3, No. 3, Sptmbr 212. [26] G. Yin, A Distributd Gnration Islanding Dtction Mthod Basd on Artificial Immun Systm, Transmission and Distribution Confrnc and Exhibition: Asia and Pacific, 25 IEEE/PES, pags: 1 4, 25. [27] J. L, B. Min, T. Kim, D. Yoo, and J. Yoo, "Activ Frquncy with a Positiv Fdback Anti-islanding mthod basd on a robust PLL algorithm for grid-connctd PV PCS", Journal of Powr Elctronics, Vol. 11, No. 3, pp , May 211. [28] H. Zinldin, and M. Salama, "Impact of Load Frquncy Dpndnc on th NDZ and prformanc of th SFS islanding dtction mthod", IEEE Transactions on Industrial Elctronics, Vol. 58, No. 1, pp January 211. [29] X. Wang, W. Fritas, W. Xu, and V. Dinavahi, "Impact of DG Intrfac Controls on th Sandia Frquncy Shift antiislanding mthod", IEEE Transactions on Enrgy Convrsion, Vol. 22, No. 3, pp Sptmbr 27. [3] IEEE Std , IEEE Rcommndd Practic for Utility Intrfac of Photovoltaic (PV) Systms, Institut of Elctrical and Elctronics Enginrs, Inc., Nw York, NY. [31] Y. Zhang, H. Sun and L. Lops An islanding dtction nhancr for a systm with multipl photovoltaic invrtrs 2nd Canadian Solar Buildings ConfrncCalgary, Jun 1 14, 27. [32] L. d Castro and F. Von Zubn. Larning and Optimization Using th Clonal Slction Principl, IEEE Transactions on Evolutionary Computation, Spcial Issu on Artificial Immun Systms, 6(3), pp , P a g

8 Intrnational Journal of Tchnical Rsarch and Applications -ISSN: , Volum 3, Issu4 (July-August 215), PP [33] L. d Castroand F. Von Zubn, Artificial Immun Systm: Part 1 Basic Thory and Applications, Tchnical rport, Dc [34] D. Dasgupta and N. Okin, Immunity-Basd Systms: A Survy, In Procdings of th IEEE Intrnational Confrnc on Systms, Man and Cybrntics, Oct [35] L. d Castro and J. Timmis, Artificial Immun Systms : A Novl paradigm to Pattrn Rcognition, In Artificial Nural Ntworks in Pattrn Rcognition, SOCO- 22, Univrsity of Paisly, UK, 22. [36] X. Wang, J. Chng, Z. Yin, M. Guo, A nw approach of obtaining rsrvoir opration ruls: Artificial immun rcognition systm, Exprt Systms with Applications 38 (211) P a g