FLICKER CONTRIBUTION OF INDUCTION GENERATORS IN WIND ENERGY CONVERSION SYSTEMS

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1 Journl of Eletril Engineering FLIKER ONTRIUTION OF INDUTION GENERTORS IN WIND ENERGY ONVERSION SYSTEMS k. s. Sndhu sudhir Shr 2 Professor, Deprtent of Eletril Engineering, Ntionl Institute of Tehnology, Kurukshetr, INDI 2 ssoite Professor, Deprtent of Eletril Engineering, DV Institute of Engineering nd Tehnology, Jlndhr, INDI kjssndhu@rediffil.o, sudhir.@gil.o strt This pper gives fous on the fliker eission y indution genertors (IG) generlly used in wind energy onversion systes. MTL sed SIMULINK odels re developed to investigte the effets when IGs re operting under self nd grid onneted ode. Siulted results s otined re used to investigte the fliker eission in single nd ulti-hine opertion. It lso inludes the effet of swithing sequenes of inoing genertors on fliker eission in se of ulti-hine opertion. Keywords: Fliker; Indution genertor; Power qulity; Wind genertion; SIMULINK odel.. INTRODUTION Fliker is one of jor preter ffeting the power qulity of indution genertors. Wind power plnts produes Fliker eission due to flutution in the power output of wind genertor due to vritions in wind speed, effet of tower shdow nd wind shers. The wind whih is the driving fore is vrying ontinuously nd results into fliker eission whih leds to the power qulity prole. Fliker produed y indution genertors propgte fro Point of oon oupling (P) to ustoer preises through trnsforers, series openstors nd trnsission/ distriution lines. The fliker eission fro single or ulti turines wind generting systes y e ssessed fro the reoendtions in IE nd IE ording to stndrd EN 56, long ter fliker liit required hs to e less or equl to. during 95% of week. Hene wind energy onversion systes need to e investigted regrding fliker eission. The fliker eter for esureent of fliker is given in IE/ IEEE stndrd nd se is used y ny reserhers []. Leonrd et l [2] presented disrete odel of fliker eter s per the IE Stndrd. The odel ws used lone or in ointion with SIMULINK SiPowerSystes lok set, for esureent of fliker. The odel preters were tken for fliker esureent in 6 Hz syste. ertol et l [3] developed fliker eter odel in MTL/ SIMULINK environent nd vlidted for fliker eission studies. Roohollh et l [4 & 5] used different softwre s to odel eletril, ehnil nd erodyni prts of wind energy onversion systes for power qulity studies with in fous on fliker eissions for wind power plnt hving lrge nuer of wind genertors s well s for stndlone syste operting with diesel genertor. MTL/ SIMULINK softwre ws used to odel the eletril systes. i [6] ied his reserh work to iproves the onventionl fliker esureent ethods nd with ore types of lps. Py et l [7] proposed siple ethod to study the soure of fliker in power syste. It ws esy to ipleent this syste in esuring instruents. Wng et l [8] showed the esured vlues of flikers generted y oeril wind power genertion syste in Tiwn. It ws found fro the esured results tht ΔV flikers ontriuted y four WTIGs were well elow the stndrd vlues. Hsu et l [9] investigted the fliker eission during high power outputs nd lso presented the reltion etween two short ter severity indexes i.e. ΔV nd P st. Ppdopoulos [] investigted fliker eission onsidering different types of wind turines, operting onditions, network hrteristis nd loding et. The fliker index ws given y odeling nd ipleenting the lgorith for lultion of fliker. Vn et l [] nlyzed the ftors effeting the fliker eission. The fliker indued y the opertion of grid-onneted wind turines ws estited using SVR. The PSIM softwre nd MTL progre were used to otin the short ter fliker severity.

2 Journl of Eletril Engineering In this pper IE/ IEEE fliker eter is used in MTL/ SIMULINK to study the fliker eission due to ny hnge in the operting onditions of indution genertors. The ipt of hnge in wind speed, lod, opensting pitors nd swithing opertions on fliker eission re investigted. For the first tie, sinusoidl signl hs een onsidered to ount ny disturne in the wind speed. Single nd ulti-hine opertion under Self exited ode nd grid onneted ode re investigted. Fig. IEEE fliker eter 2. THE FLIKER METER The flikers n e onsidered s low- frequeny odultion of the network voltge t 5 Hz. The flikereter is n instruent whih is used to seprte the rrier wve fro the odulting wve. It weights the effets of the ltter sed on hun sensitivity to the disturne, nd generte the instntneous senstion of the fliker. ording to IE/IEEE stndrds, the fliker severity n e of two types i.e. short-ter vlue, P st, esured over inutes period, or long ter vlue, P lt, lulted fro sequene of P st over period of 2 hours. P st n e expressed s: Fig.2 lok Digr of IEEE fliker eter P ୱ୲ = ඥ.34P.ଵ +.525P ଵ +.657P ଷ +.28P ଵ +.8P ହ () In eqution () the perentiles P., P, P 3, P, nd P 5 re the fliker levels exeeded for.,, 3,, nd 5% of the tie during the period under oservtion. The uultive proility funtion gives the exeeded fliker levels. Long ter fliker eission is lulted fro 2 onseutive P st vlues (i.e. for two hours durtion) s per the following forul: 45 RMS Ref Vlue Divide u 2 Mth Funtion e-5s e-3s+ Polynoil s s+ High Pss Filter Gin e-5s e-3s+ Polynoil.5499s s s Lp-eye-rin-hin e-5s e-3s+ Polynoil 2.698s e-4s s+ Lp-eye-rin-hin 2 In య P ୪୲ = ට ଵ ଵଶ ଵଶ ୨ ଵ Pst ୨ ଷ.. (2) u 2 Mth Funtion sqrt.3s+ Mnoriztion Mth Gin in rin Funtion2 Out IE/IEEE stndrds sed fliker eter odel is developed in MTL/SIMULINK nd is used in this pper, s used y soe of the reserhers [, 3, 4 & 5]. The IE/IEEE fliker eter s shown in figure y e represented vi lok digr s shown in figure 2 oprising of five su loks. Figure 3 shows the SIMULINK odel of fliker eter s disussed ove nd the se is ipleented to investigte the fliker eission in wind energy onversion syste. Fig. 3 SIMULINK odel of fliker eter 3. FLIKER ONTRIUTION OF SELF EXITED INDUTION GENERTORS 3. Single hine syste Figure 4 shows the MTL/ SIMULINK odel of self exited indution genertor long with IEEE fliker eter s disussed in setion II. In this odel the wind vritions re reted y odulted wve s shown in figure 5. s shown wind speed vritions inluding the durtion of hnge is possile y ontrolling the gnitude & frequeny of the odulted wve. Tle, shows the siulted results on 6 kw, 4V, 5 Hz, 4-pole indution genertor [ppendix I]. 2

3 Journl of Eletril Engineering P_Wt [P_WT] Goto Tle - Fliker eission y SEIG due to hnge in gnitude nd rte of hnge of wind speed vritions ontinuous pow ergui P kw Vf _ Synhronous ondenser S Exittion V I V I Fliker Meter Out Pst To Workspe5 V_l I_l Vf [_L] Goto2 Gin Gin V I [_s] Goto Sine Wve.2 onstnt dd V_LF Fro2 V I WT V I V(pu) Freq wt Sin_os Disrete 3-phse PLL P Q w [Q_WT] Goto3 <Rotor speed (w)> signlrs RMS Goto4 -K + v - [_L] [_s] [P_WT] [Q_WT] Sope In Vphse Q_Wt Rte of hnge of Wind Speed.99 pu to.5pu Wind Speed Vritions.97 pu to.7 pu.92 pu to.2 pu Instntneous Fliker Eission 2 Hz Hz Hz Hz Hz Hz Fig. 4 SIMULINK odel of SEIG for fliker study Fig. 5 Vritions in wind speed Tle shows the vritions in instntneous fliker eission with hnge in speed nd gnitude of wind vritions. It is oserved tht; For given rnge of wind speed vritions instntneous fliker first inreses with rte of hnge of (frequeny) wind speed vritions nd then gin strt deresing. This gives ritil vlue of frequeny of wind speed vritions i.e. Hz, whih results into the xiu vlue of fliker. For given vlue of rte of hnge of (frequeny) wind speed vrition, fliker t hine terinls inreses with inrese in the rnge (gnitude) of wind speed vritions. The effet of pitor nks used for openstion & swithing of pitor nk re investigted for instntneous fliker eissions nd re tulted in tle 2. Tle-2 Effet of pitor vlue nd pitor swithing on instntneous fliker eissions Prtiulrs Single vlue pitor nk t strt Single vlue pitor nk t strt Single vlue pitor nk t strt pitor nk no t strt nd pitor nk no 2 t se pitor nk no t strt nd pitor nk no 2 t se pitor nk no (kvr) pitor nk no2 (kvr) Lod (kw) Inst fliker Ter. Volt Frequeny

4 P Vf_ In Vf Out V I signlrs ontinuous Wek grid powergui Vphse e- Goto Phse Voltge rssignl RMS V I V I Fliker Meter v + - Instntneous f liker V I F_Soure Three-Phse Prllel RL Lod F_l F_g2 F_g3 F_g VI 3 VI VI 4 V I V I V I V I V I V I dd w w w synhronousmhine SI Units dd 6 64 synhronous Mhine SI Units2 dd synhronous Mhine SI Units3 <Rotor speed (w)> <Rotor speed (w)> <Rotor speed (w)> Journl of Eletril Engineering It is oserved fro the ove tle tht fliker eission whih is dependent upon the terinl voltge vries due to ny hnge in the opensting pitor nk. This shows tht the fliker eissions y e ontrolled y pproprite seletion of pitor nk long with its swithing instnt. 3.2 Multi-hine syste Multi hine odel of self exited indution genertors feeding resistive lod for investigting fliker eission is shown in Fig. 6. Three wind genertors of 6 kw, 75kW nd 7.5 kw [ppendix -I] pities re used for investigting the fliker eission due to swithing. The synhronous ondenser is used for initil voltge uildup in the SEIG s. The different swithing sequenes for inoing hines s onsidered re tulted in tle 3. Tle - 3 Swithing sequenes for SEIG of different rtings Swithing Detils Sequ no 6kW t strt, 75kw t se, 7.5 kw t 2 se 7.5 kw t strt, 75kw t se, 6 kw t 2 2 se 75 kw t strt, 7.5kw t se, 6 kw t 3 2 se ll hines siultneously t strt 4 ll sequenes s per tle -3 results into the se vlue of fliker eissions s given elow: i. Mgnitude =.pu, frequeny = 3Hz fliker =.68 ii. Mgnitude =.pu, frequeny Hz fliker =.2662 iii. Mgnitude =.pu, frequeny 25Hz fliker =.74 ontinuous pow ergui [V_Ph_L] Vphse kw Synhronous ondenser e-8 Exittion Fliker Meter Gin S.2852 Pst V I V I To Workspe5 Gin V I e-5 Fig. 6 Siulink odel of SEIG ulti- hine syste + - v V_LF Fro2 RMS V(pu) SEIG 2 Freq wt Sin_os Disrete 3-phse PLL 9.2 SEIG SEIG FLIKER ONTRIUTION OF GRID ONNETED INDUTION GENERTOR s the voltge nd frequeny re ontrolled y grid in se of stiff grid, hene in single or ulti-hines opertion no hnge in voltge or frequeny is oserved t point of oon oupling (P). Sine fliker is the phenoenon relted with voltge vritions, hene no fliker ppers in strong grids. The progrle voltge soure is used stiff grid hving short iruit rtio of * 6 nd X/R rtio of Single hine syste onneted to wek grid: The SIMULINK odel of single hine onneted to wek grid for fliker investigtion t vrying wind is shown in Fig.7. In this odel the wek grid is reted using voltge soure lok nd the of the wek grid s short iruit rtio is tken s * 5 nd X/R rtio is. The instntneous fliker eission is oserved with wind vritions t different rtes. 6kW indution genertor [ppendix I] is inserted in the iruit t.5 se fter strt of siultion. V I Figure. 7. SIMULINK odel of grid onneted ulti hine syste for fliker study Tle-4 Instntneous fliker eission y GIG onneted to wek grid Rte of hnge of wind vritions Mgnitude of wind vrition.3 pu.5 pu. pu Instntneous Fliker eissions 2 Hz Hz Hz Hz Hz Hz

5 Journl of Eletril Engineering Tle 4 gives the instntneous fliker eissions y GIG onneted to wek grid with different gnitudes & rtes of wind vritions. nlysis of this tle yields the se oservtions s in se of SEIG (Tle ). This lso gives ritil vlue of frequeny of wind speed vritions i.e. Hz, whih results into xiu vlue of fliker. 4.2 Multi-hine syste onneted to wek grid: Three hines of se rting: Siulted results of three different swithing sequenes for low, ediu nd strong wind vritions re investigted for three hines of 75 kw re operting in wek grid is shown in tle 5.The Fig. 8 to Fig. shows the fliker eission, lod terinl voltge nd frequeny t lod terinls for the worst se of fliker eissions (without pitor nk). Tle- 5 Instntneous fliker eission y GIG of se rting with different swithing sequenes Swithing Detils 75 kw t strt, 75kw t.5 se, 75 kw t se 75 kw t strt, nd two IG of 75 kw eh t.5 se ll hines of 75 kw eh, swithed on siultneously Swithing Sequ no Mgnitude =. rte of hnge of wind vritions =3 Hz Instntneous fliker eissions Mgnitude =. rte of hnge of wind vritions = Hz Mgnitude=. rte of hnge of wind vritions = 25 Hz With dditionl pitor nk of 3kVR t the terinls of one hine Swithing sequene no 3 3 Voltge t lod terinls when three hines of se rting swithed on siultneously.8 Mgnitude of wind vritions =. Rte of hnge of wind vritions = 3 Hz Instntneous fliker.2..8 Voltge in volts Tie in se Fig.8 Instntneous fliker eissions when three hines of se rting swithed on siultneously t.5 se Tie in Se Fig.9 Terinl voltge when three hines of se rtings swithed on siultneously t.5 se 5

6 Journl of Eletril Engineering Fig. Frequeny t lod terinls when three hines of se rting swithed on siultneously t.5 se Fro the tle 5 nd Fig. 8 to Fig., it is oserved tht: Frequeny Hz Frequeny t lod terinls Mgnitude of wind vritions =. Rte of hnge of wind vritions = 3 Hz Tie in Se Mxiu fliker eission ours when ll the hines re swithed on siultneously. Lowest fliker eissions re seen t swithing sequene -2, with wind vrition frequeny 25 Hz nd gnitude of. pu. The use of pitor to iprove the voltge lso results in inresed fliker eission s the highest fliker eissions ppers t sequene 3 when pitor nk of 3 kvr is onneted t the terinls of hine -III Terinl voltge s shown in Fig is redued to low vlue thn the rted vlue. Vritions in the frequeny re lso oserved. Three hines of different rting: In this se three indution genertors of different rtings i.e. IG no is of kw, IG no 2 is of 75 kw nd IG no 3 is of 37 kw re onsidered. The totl pity of the fr is lost se s with three hines of se rting. The fliker eissions t three different types of wind vritions for seven different swithing sequenes is investigted nd tulted in tle 6. Fig. to Fig.3 shows the vritions in ove preters when pitor nk of 3 kvr is onneted t the IG III terinls. Tle-6 Instntneous fliker eission t different swithing sequenes (Three hines of kw, 75kW nd 37 kw) Swithing Detils kw t strt, 75kW t.5 se, 37 kw t se 75 kw t strt, 37 kw t.5 se, kw t se 37 kw t strt, kw t.5 se, 75 kw t se 37 kw t strt, kw nd 75 kw t.5 se 75 kw t strt, kw nd 37 kw t.5 se kw t strt, 37 kw nd 75 kw t.5 se ll hines swithed on siultneously Instntneous fliker eissions Sequ nos Mgnitude of wind vrition=. Rte of hnge of wind vritions = 3 Hz Mgnitude of wind vrition=. Rte of hnge of wind vritions = Hz Mgnitude of wind vrition=. Rte of hnge of wind vritions = 25 Hz With dditionl pitor nk of 3 kvr onneted t the terinls of IG -III

7 Journl of Eletril Engineering Fig. Instntneous fliker eissions when three hines of different rtings swithed on siultneously t. se with 3 kvr pitor nk t terinls of IG III Voltge in volts Fig. 2 Voltge t lod terinls when three hines of different rtings swithed on siultneously t. se with 3 kvr pitor nk t terinls of IG -III Frequeny inhz Instntneous fliker eission Mgnitude of wind vritions =. Rte of hnge of wind vritions = Hz pitor nk = 3kVR Swithing sequene -7 (Three hines of different rting) Tie in se Tie in se Swithing sequene -7 (hines ofdifferent rting) Frequeny t lod terinls (swithing sequene -7) Mgnitude of wind vritions =. pu Rte of hnge of wind vritions = Hz pitor nk = 3 kvr Tie in se x 4 Fig. 3 Frequeny t lod terinls when three hines of different rtings swithed on siultneously. se with 3 kvr pitor nk t terinls of IG-III The swithing sequene no 7 gives the xiu vlue of instntneous fliker eissions. t this swithing sequene the terinl voltge is found redued thn rted vlue. Vritions in the frequeny re lso reorded. When pitor nk of 3 kvr is used t the terinls of IG III to iprove the voltge profile t lod terinls, lrge inreses in fliker eission is seen. It is lso oserved tht the fliker eission hs rossed the stndrd vlue of fliker eissions. ut siultneously the voltge profile t lod terinls s shown in Fig.2 is found iproved. It lso results into n iproveent in frequeny vrition 5 DISUSSIONS This pper inludes disussions relted to one of the jor power qulity issue i.e. fliker. For suh investigtions IEEE stndrd sed fliker eter is used. SIMULINK odels s listed elow inludes the wind vrition representtion through odulted wve of sinusoidl for SIMULINK odel of SEIG(single hine nd ulti hine opertion) SIMULINK odel of GIG(single hine nd ulti hine opertion). onneted to stiff grid. onneted to wek grid nlysis of siulted results s disussed in the hpter yields following onlusions;. SEIG (single hine opertion) For given rnge of wind speed vritions instntneous fliker first inreses with rte of hnge of (frequeny) wind speed vritions nd then gin strt deresing. This gives ritil vlue of frequeny of wind speed vritions i.e. Hz, whih results into the xiu vlue of fliker. For given vlue of rte of hnge of (frequeny) wind speed vrition, fliker t hine terinls inreses with inrese in the rnge (gnitude) of wind speed vritions. Fliker eission whih is dependent upon the terinl voltge vries due to ny hnge in the opensting pitor nk. This shows tht the fliker eissions y e ontrolled y pproprite seletion of pitor nk long with its swithing instnt. 2. SEIG (ulti- hine opertion) Mgnitude nd rte of hnge of wind speed effets the fliker eissions. Swithing sequene hs no effet on fliker eission. 3. GIG (onneted to stiff grid) Due to presene of stiff grid, no effet on fliker eission. 4. GIG (single hine onneted to wek grid) Se effets s disussed in se of SEIG s single hine. 7

8 Journl of Eletril Engineering 5. GIG (ulti- hine onneted to wek grid) Mgnitude nd rte of hnge of wind speed effets the fliker eissions. Mxiu fliker eissions our when ll the hines re swithed on siultneously. The use of pitor to iprove the voltge lso results in inresed fliker eissions. Terinl voltge flls to low vlue Vritions in frequeny re oserved. 6 ONLUSION Fro the ove disussions, it y e onluded tht the opertion of ny hine (single hine/ ultihine opertion) will led to severe fliker in se it is sujeted to wind vritions of lrge gnitude nd frequeny of vritions lose to ritil vlue. In ddition high vlue of fliker y e voided y suitle seletion & swithing of opensting pitors. Siultneous swithing of nuer of hines in wind fr y led to fliker prole REFERENES. IEEE Std (doption of EI/IE :997+:23) IEEE Reoended Prtie for Mesureent nd Liits of Voltge Flututions nd ssoited Light Fliker on Power Systes. 2. Leonrd W. White, Suhshish htthry, Disrete Mtl Siulink Flikereter Model for Power Qulity Studies IEEE Trnstions on Instruenttion nd Mesureent, Vol. 59, No. 3, Mrh 2 3. ertol, G.. Lzroiu, M. Rosi, nd D. Zninelli Mtl-Siulink Flikereter Model for Power Qulity Studies IEEE th Interntionl onferene on Hronis nd Qulity of Power, pp , 24 Mhine Rting (kw) 4. Roohollh Fdeinedjd, Gerry Moshopoulos nd Sondeep ssn, Fliker ontriution of Wind Power Plnt with Single nd Multiple Representtions IEEE nd Eletril Power onferene, pp 74-79, Roohollh Fdeinedjd, Gerry Moshopoulos nd Sondeep ssn, Fliker ontriution of wind turine in stnd-lone wind diesel syste ndin onferene on Eletril nd oputer Engineering, EE, pp , My 4-7, Rong i Fliker Intertion Studies nd Flikereter Iproveent [online] ville : 7. Frrokh Py,. Mirzein Dehkordi, M.S. Sdri, M. Molle n Energy Method for Deterintion of fliker Soure t the Point of oon oupling IEEE Interntionl onferene on oputer s tool, EUROON, pp 65-62, Septeer 9-2, Li Wng, Dong-Jing Jee, Shing-Shong hen, Shing-in Tseng, Ko-Hu Liu, Tsu-Jin Lin, I-Ting Hung, Shu-wei Liu, Jun-Ho Lin, You-Ren Lin, nlysis of Mesured Fliker ontriuted y oeril Wind Power Genertion in Tiwn, Power nd Energy Soiety Generl Meeting - onversion nd Delivery of Eletril Energy in the 2st entury, 2-24 July V. Hsu, Y.J. Lu,.N. Fliker esureents t n industril power network with wind turines IEEE Power Engineering Soiety Generl Meeting, 26.. Ppdopoulos, M.P. Ppthnssiou, S.. Tentzerkis, S.T. oulxis, N.G. Investigtion of the Fliker Eission y Grid onneted Wind Turines Proeedings. 8th Interntionl onferene on Hronis nd Qulity of Power, pp 52 57, Tn Luong Vn, Thnh Hi Nguyen, Kyung-Hyun Ki, nd Dong-hoon Lee SVR-sed Fliker Estition of wind power systes The Interntionl power eletronis onferene, 2. PPENDIX I: Preters of hines used for siultion. Sttor Resistne (R s ) pu Rotor Resistne (R r ) pu Sttor lekge indutne (L s ) pu Rotor lekge indutne (L r ) in pu Mutul Indutne (L ) in pu