Wavelet Packet Transform Based Power Quality Analysis تحليل جودة القدرة باعتماد تحويله حزمة المويجة

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1 34 Wvelet Pket Trnsform Bsed Power Qulity Anlysis Dr. Adel A. OBED Eletril Deprtment, College of Engineering, Bsrh University. Abstrt: This pper presents dignosti tehnique for power qulity nlysis ginst different disturbnes in eletril power soure. The presented tehnique utilizes wvelet pket trnsform (WPT)-bsed proposed lgorithm for monitoring nd detetion vrious disturbnes ourring in supply voltge signl nd in supply frequeny. The vlues nd the time lotions for low nd high frequeny oeffiients re determined up to level six nd ompred with threshold determined from the opertion of helthy soure. The proposed tehnique is tested on ertin ses nd the simulted results indite tht this tehnique is effetive for deteting nd monitoring different mentioned disturbnes. Keywords: Wvelet pket trnsform, Disturbnes monitoring nd detetion, Power qulity تحليل جودة القدرة باعتماد تحويله حزمة المويجة د. عادل احمد عبيد قسم الهندسة الكهرباي ية- كلية الهندسة- جامعة البصرة الخلاصة : يقدم هذا البحث تقنية مميزة لتحليل جودة القدرة تجاه مختلف الاضطرابات في مصدر القدرة الكهرباي ية. تستخدم هذه التفنية برنامج مقترح لمراقبة وكشف مختلف الاضطرابات خلال اشارة فولتية المصدر وتردده باعتماد تحويلة حزمة المويجة. تم حساب القيم والموقع الزمني لمعاملات الترددات الواطي ة والعالية ولغاية المستوى السادس وقورنت مع قيم بداي ية تم الحصول عليها من حالات تشغيل لمصدر خالي من الاضطرابات. بينت نتاي ج المحاكا ة با ن التقنية المستخدمة فعالة لمراقبة وكشف مختلف الاضطرابات المشار اليها. - Introdution With the development of power industry nd the wide pplitions of solid stte swithing power supplies nd to void undesirble stresses in eletril lods whih my led to mny modes of filures, it is neessry to protet it from different disturbnes introdued from the soure. Moreover the need for ondition monitoring hs inresed reently beuse of the widespred use of utomtion nd onsequent redution in diret mnmhine interfe to supervise ny system opertion. Monitoring is the grphil tend of the lod opertion for the purpose of detetion, nlysis nd orretion of the system problems before the filure tkes Bsrh Journl for Engineering Siene / ple []. The detetion nd orretion of ny disturbne leds to inresing lod vilbility nd performne voiding dmge, reduing spre prts, inventories nd brekdown mintenne []. The nture of the output of power soure, espeilly solid stte swithing power supply, involves vrition in the eletri voltge nd urrent, suh s voltge sg, swell, dips, flutution, momentry interruption, hrmonis, nd trnsient osilltions, using mlfuntion, instbilities, short lifetime, filure of the eletril equipments [3-8]. These vritions lie under power qulity problem nd to improve power qulity, it is required مجلة البصرة للعلوم الهندسية /

2 35 to find wys to mitigte the soure power supply. A trditionl pproh for power qulity uses fst Fourier trnsform (FFT) to nlyze hrmoni ontents ontined in the power signl [9,]. However FFT is bsilly stedy stte nlysis pproh. An ttempt to develop n lgorithm bsed on disrete sttionry wvelet trnsform (SWT) is used to determine the mplitude of the hrmonis present in the power signl from the oeffiients omputed by ontinuous wvelet trnsform (CWT) nd wvelet-neurofuzzy ombined system [,]. The seprte FFT routine nd severl neurl networks re required long with the fetures extrted from the wvelet multiresolution nlysis. This pper ims to propose dignosti tehnique for monitoring nd detetion of the vritions of the power soure signl (voltge sg, swell, interrupt, spike, hrmonis) nd the vritions in soure frequeny, bsed on wvelet pket trnsform. The WPT is used to lulte the low frequeny oeffiients up to level six nd up to level two for high frequeny oeffiients nd to lulte the energy t these levels through the Shnnon entropy formul. The high frequeny detils, dd, is used to onstrut n lgorithm for disturbnes nlysis. The simultion results give trip signl t instnt with less thn one yle of the disturbne in ll ses studied. - Wvelet Pket Trnsform (WPT) Wvelet pket trnsform is type of wvelet-bsed signl proessing in wy tht eh level of resolution (otve) j j onsists of boxes generted by tree of low pss filter (LPF) nd high pss filter (HPF) opertions. The frequeny bndwidth of box dereses with growing otve number i.e. with inresing otve number, the frequeny resolution beomes higher while the time resolution is redued. Strting with disrete signl f[n] with length, the first level, j=, deomposition produes two subbnds disrete signls [ / ] nd d [ / ] s follows [,3]:- [n] = g(k) f (n k) () d [n] = h(k) f (n k) () where [n] nd d [n] re the first level pproximtions nd detils respetively, k is n integer nd g(n), h(n) re the LPF nd HPF ssoited with seleted mother wvelet funtion respetively. The output of both LPF nd HPF re downsmpled by two t the end of eh filtering stge in order to inrese the frequeny resolution nd to ensure the time loliztion of eh frequeny subbnd. The seond level of deomposition will produe four subbnds due to the deomposition of both [ / ] nd d [ / ] using the sme set of filters. These subbnds re [ / 4] d [ / 4], d [ / 4] nd dd [ / 4] s follows [,3]:- [n] = g(k) (n k) (3) d [n] = h(k) (n k) (4) d [n] = g(k) d (n k) (5) dd [n] = h(k) d (n k) () A higher level of deomposition n be produed in the sme proedure bove. The min dvntge of WPT over ontinuous nd disrete wvelet trnsform is better, more urte nd more detiled representtion of the deomposed signls [3]. Also, wvelet pket bsis funtions re lolized in time offering better signl Bsrh Journl for Engineering Siene / مجلة البصرة للعلوم الهندسية /

3 3 pproximtion nd deomposition. These bsis funtions re generted from one bse funtion t sle s, diltion nd trnsltion b s follows [3]: w s,,b (n) = j/ W ( j (n b)) (7) where W (n) is the wvelet funtion oeffiient mtrix. In WPT, disrete signl f [n] is represented s sum of orthogonl wvelet bsis funtions w s,, b (n) s follows: f [n] w (8) = s b s,,b [n] W [n] The implementtion proedure of the WPT for two levels is shown in the deomposition tree of Fig.. G G f[n] H d H d G d Level Level Level H dd Fig. Two levels of deomposition by WPT 3- Soure Disturbnes Detetion Using WPT Coeffiients The soure power qulity omprises vrious kinds of disturbnes in the supply voltge nd frequeny. In ll ses, the signl wveforms re generted from omputer using Mtlb ode. The bsi frequeny is 5 Hz nd the bsi voltge mgnitude is V rms whih is normlized. The smpling frequeny is.5 kh Z. Dubehies 4 (db4) is used s mother wvelet funtion. The Mtlb, wvelet toolbox funtions [4] re used to deompose the originl signl into low nd high frequeny oeffiients. 3- Soure Voltge Disturbne Anlysis -Voltge Sg: This problem ours due to fult swithing of hevy lod or strting of lrge motors. The mplitude of the voltge drops by to 9 perent of the rted vlue. Figure (-) shows the normlized pure signl nd Fig.(-b) shows normlized signl for 5% sg in the voltge wveform during three yles. - Voltge Swell: If norml voltge inreses by to 9 perent, then it is known s voltge swell. Figure (-) shows normlized 5% swell in the voltge wveform during three yles. - Voltge Interruption: It mens tht the voltge is lost momentry on power system. Suh disturbne desribes drop of 9 to perent of the rted system voltge lsting for.5 yle to min. Figure (-d) shows normlized % momentry interruption lsting for ms. - Spike Voltge Osilltions: The voltge disturbne is lled osilltory if it lsts for time durtion shorter thn sgs or swells. It n lso be lssified s impulsive, nothed or spike. Figure (-e) shows normlized voltge signl with spike for ms in two yles. - Voltge Hrmonis: If the signl ontins hrmonis like 3 rd, 5 th, et., then this soure is lled voltge hrmoni soure. Figure (-f) shows normlized pure voltge with the 5 th hrmoni in 3 yles. The Shnnon entropy-bsed riteri is used to lulte the energy of the signl oeffiients t eh level of deomposition of low nd high frequeny s follows [4]:- = i i ( f ) E f log (9) i where E is the Shnnon entropy nd f is the nlyzed signl. The bsolute entropy of the distorted funtion t eh level is Bsrh Journl for Engineering Siene / مجلة البصرة للعلوم الهندسية /

4 37 ompred with the ssoited pure funtion s follows:- j j p E = E E () where j denotes the number of level of resolution of the WPT nd E is the differene in entropy vlues between the distorted nd the pure (p) signl. Tble presents the feture vetors of the equtions 9 nd whih gives the differene in entropy vlues for j d = E, j,,...,, E nd E dd. Tble feture vetors of equtions 9 nd for disturbnes in soure signl signl E type d E E dd sg swell interrupt spike hrmoni From Tble, it n be seen tht the pttern of feture vetors for different voltge disturbne events re ble differentible effetively between themselves. Level two, dd, detils hs signifint differene in energy of distorted nd helthy signls. The high frequeny detils dd vnished t levels bigger thn two. Therefore, it n be onsidered s n extrtion fetures to design proposed lgorithm for dignosis of different disturbnes ourred in power soure voltge signl. The detils dd for eh voltge disturbne signl re drwn in Fig.3 (-f) s funtion of smple number. 3- Soure Frequeny Disturbnes Anlysis The bsi frequeny onsidered in this nlysis is 5 Hz. Any disturbne in the supply frequeny will ffet the onneted lods. The soure frequeny my hnge due to momentry hnge in prime mover speed or disturbne in the solid stte swithing power supply. Figure 4 reflets the ± 4% disturbne in the supply frequeny for ms. The feture vetors of the equtions 9 nd whih give the differene in entropy vlues for j d = E, j,,...,, E nd E dd re given in Tble. The detils dd for the mentioned disturbnes re shown in Fig.5 whih lso n be onsidered s extrtion fetures to design the sme lgorithm for dignosis of disturbnes in supply frequeny. Tble feture vetors of eqution 9 nd for disturbnes in soure frequeny f E E dd ±.% ±.4% ± % ± 4% Bsrh Journl for Engineering Siene / مجلة البصرة للعلوم الهندسية /

5 38 () () () () (d) (d) (e) (e) (f) (f) Fig. Voltge signls () helthy sg () swell (d) interrupt (e) spike (f) hrmonis. Fig. 3 Seond level high frequeny detils dd for voltge signls () helthy sg () swell (d) interrupt (e) spike (f) hrmonis. Bsrh Journl for Engineering Siene / مجلة البصرة للعلوم الهندسية /

6 39 () () Fig.4 Voltge signl with disturbne in frequeny Fig. 5 Seond level high frequeny detils dd for () inrese by 4% derese by 4%. disturbne in frequeny () inrese by 4% derese by 4%. 4- Proposed WPT Disturbnes Detetor In order to detet nd monitor ny disturbne, it is neessry to build the extrtion fetures. A suessful fetures involve the identifition of bnorml onditions by the mthemtil modeling of the omplete system or the nlysis of fult signtures resulting from different trnsient disturbnes. A signture nlysis method is used for the present proposed WPT disturbne detetor. The signl is deomposed up to seond level of resolution by WPT using the seletion mother wvelet " db4". The proposed method looks t the seond level high frequeny detils dd oeffiients in different types of disturbnes. The seond levels dd oeffiients re given in Figs.3 nd 5. The simulted results of these figures re used to nlyze the signtures of vrious disturbnes in voltge nd frequeny. In the helthy signl, the seond level dd oeffiients re round zero while the ssoited dd oeffiients for ny type of disturbnes will inlude threshold vlue represented by Shnnon entropy in the lst olumn in Tbles nd for disturbnes in voltge signl nd supply frequeny respetively. These vlues n be used s extrtion fetures for the proposed WPT disturbnes detetor. The proposed WPT lgorithm is given in the flowhrt of Fig.. Firstly, the three-phse voltge signls re red nd smpled. The smpled signls re pssed through high pss filter to find the first level d V, d Vb nd d V. The outputs re downsmpled by two nd then pssed through nother high pss filter to onstrut the detils dd V, dd Vb nd dd V. If the bsolute vlue of dd oeffiients for eh voltge signl is in the rnge of voltge disturbne threshold (V thresh.), then it detet signl for disturbne in the voltge signl. And if the bsolute vlue of dd oeffiients for eh voltge signl is in the rnge of frequeny disturbne threshold (f thresh.), then it detet signl for disturbne in the supply frequeny. The threshold is seleted by the mximum bsolute vlue of the WPT oeffiients of the seond level of deomposition during ny disturbne ondition. Bsrh Journl for Engineering Siene / مجلة البصرة للعلوم الهندسية /

7 4 Red V Red V Red V d V = H * V d Vb = H * Vb d V = H * V d V = downsmpled d V by d Vb = downsmpled d V b by d V = downsmpled d V by if dd V dd V = H * d V dd Vb = H * d Vb dd V = H * d V V thresh. if dd V thresh. V b if dd V V thresh. b V Trip Signl F Trip Signl if dd V f thresh. if dd V b f thresh. if dd V f thresh. 5- Testing of the Proposed WPT Algorithm The simulted setup of the disturbnes detetion nd monitoring inorporting the protetion iruit for onneted lod is shown in Fig.7. The three-phse signl is onsidered s input to the WPT lgorithm while the ontrol signl is its output. The ontrol signl n be used for ontrolling tri swith to isolte the lod from the supply if n undesirble disturbne is ourred.. Figures 8()-8(d) show the detetor response nd phse () voltge signl for two kinds of disturbnes in voltge signl, Fig.8()-8, (sg nd spike) nd two kinds of frequeny disturbnes, Fig.8()-8(d), ( inrese nd derese). In eh figure, the disturbnes strt t. nd.3 se. respetively nd lsted for mse. The WPT-bsed detetion lgorithm using the seond level high frequeny oeffiients dd diretly identified ny disturbne promptly nd properly nd initited trip signl within less one yle of the disturbne ourrene. It is mentioned here tht the trip signl is not used to isolte the lod from the supply. The deision is left to the designer nd n be ontrolled by the lgorithm. 3-Ph supply Moitoring Tri Swithes Control Ciruit WPT Algorithm 3-Ph Lod Fig. Flowhrt for WPT disturbnes detetor. Fig.7 Simulted setup for disturbnes detetion nd monitoring. Bsrh Journl for Engineering Siene / مجلة البصرة للعلوم الهندسية /

8 4 () Trip Signl Time (se.) () Trip Signl (d) Time (se.) Fig.8 () A disturbnes in the voltge signl, the deteted trip signl for (), () disturbnes in supply frequeny, (d) the deteted trip signl for (). - Conlusion A dignosing method for power qulity disturbnes bsed on WPT is presented. Severl power qulity problems hve been nlyzed. The Shnnon entropy of the high nd low frequeny oeffiients re lulted for different levels of resolution nd deision to use the seond level high frequeny detils dd is onsidered s onstrution fetures to design proposed WPT lgorithm detetor. The proposed disturbnes detetor showed suessfully nd fst response for dignosing the distorted signls nd it provides n interesting nd signifint tool in deteting power qulity problem. Referenes: - L. Lin,. Hung, nd W. Hung, Review of Power Qulity Signl Compression Bsed on Wvelet Theory IEEE Conferene on Test nd Mesurement, PP35-38, 9. - M. A. S. K. Khn, T. S. Rdwn nd M. A. Rhmn, Rel Time Implementtion of Wvelet Pket Trnsform Bsed Dignosis nd Protetion of Three-Phse Indution Motors IEEE Trns. Energy Conversion, Vol.,. 3, Sep., P. K. Dsh. B. K. Pnigrhi nd G. Pnd, Power Qulity Anlysis Using S-Trnsform IEEE Trns. Power Delivery, Vol. 8,., PP. 4-4, L. Shngwel nd S. Yming, Study on the Clssifition Method of Power Disturbnes Bsed on the Combintion of S Trnsform nd SVM Multi-Clss Clssifier with Binry Tree, 3 rd Interntionl Conferene on Eletri Utility Deregultion nd Restruturing nd Power Tehnologies, PP. 75-8, 8. Bsrh Journl for Engineering Siene / مجلة البصرة للعلوم الهندسية /

9 4 5- Y. Ji, Z. Y. He nd T. L. Zng, S- Trnsform Bsed Power Qulity Indies for Trnsient Disturbnes, IEEE onferene on Power nd Energy Engineering, Asi-Pifi, PP. -4,. -. Hung, W. Hung, L. Lin nd J. Qi, Review of Power-Qulity Disturbne Reognition Using S-trnsform IEEE IITA Interntionl Conferene on Control, Automtion nd Systems Engineering, PP , Z. Wen-yun, The Detetion of Power Qulity Hybrid Disturbne Bsed on S Trnsform IEEE Conferene on Power nd Energy Engineering, Asi-Pifi, PP. -4,. 8- W. Wen-jun, F. Jin-hu nd L. Wnshn, The Applition of WPT in Compress Power Qulity Disturbne IEEE Conferene on Control nd Deision, Chinese, PP ,. 9- L. L. Li, W. L. Chn, C. T. Tse nd A. T. P So, Rel-time Frequeny nd Hrmoni Evlution Using Artifiil eurl etwork, IEEE Trns. On Power Delivery, Vol. 4,., PP. 5-59, W. L. Chn, A. T. P. So nd L. L. Li, Hrmonis Lod Signture Reognition by Wvelet Trnsform, Interntionl Conferene on Eletri Utility Deregultion Restruturing nd Power Tehnologies DRPT, IEEE, PP. -7,. - A. Elmitwly, S. Frghl, M. Kndil, S. Abdelkder, nd M. Elkteb, Proposed Wvelet-euroFzzy Combined System for Power Qulity Violtions Detetion nd Dignosis, Pro. Inst. Elet. Eng., Gen. Trns. Dist., Vol. 48,., PP. 5-,. -. C. F. Tse., Prtil Applition of Wvelet to Power Qulity Anlysis, IEEE Power Engineering Soiety Generl Meeting,. 3- G. Stng nd T. guyen, Wvelet nd Filter Bnks Wellesley, MA: Wellesley-Cmbridge, Mth Works, Mtlb, Wvelet Tool Box, Ver.. Bsrh Journl for Engineering Siene / مجلة البصرة للعلوم الهندسية /