Renewable Energy 50 (2013) 378e386. Contents lists available at SciVerse ScienceDirect. Renewable Energy

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1 Renewle Energy 5 (13) 378e386 Contents lists ville t SiVerse SieneDiret Renewle Energy journl homepge: Control of wind energy onversion system equipped y DFIG for tive power genertion nd power qulity improvement M. Boutout, L. Mokrni, *, M. Mhmoum Eletril Engineering Deprtment, Lghout University, Ghrdi street, Bp 37 G, Lghout 3, Algeri IREENA, 37 Boulevrd de l Université, Bp 46, 446 Sint-Nzire, Nntes, Frne rtile info strt Artile history: Reeived 3 Deemer 11 Aepted 3 June 1 Aville online 31 July 1 Keywords: Vrile speed wind turine AC-DC-AC PWM onverter Hrmoni urrents Ative filtering Retive power ompenstion Power qulity The im of this pper is to improve the retive power ompenstion nd tive filtering pility of Wind Energy Conversion System (WECS). The proposed lgorithm is pplied to Douly Fed Indution Genertor (DFIG) with sttor diretly onneted to the grid nd rotor onneted to the grid through k-to-k AC-DC-AC PWM onverter. The ontrol strtegy of the Rotor Side Converter (RSC) ims, t first, to extrt mximum of power under flututing wind speed. Then, depending on the rte power of the RSC, the power qulity n e improved y ompensting the retive power nd the grid hrmonis urrent due to nonliner lods. Hene, the RSC is ontrolled in order to mnge the WECS funtion s priorities, etween prodution of the mximum tive power ptured from the wind, nd power qulity improvement. The min gol of the proposed ontrol strtegy is to operte the RSC t its full pity, without ny over-rting, in terms of retive power ompenstion nd tive filtering pility. Elsewhere, the Grid Side Converter (GSC) is ontrolled in suh wy to gurntee smooth DC voltge nd ensure sinusoidl urrent in the grid side. Simultion results show tht the wind turine n operte t its optimum power point for wide rnge of wind speed nd power qulity n e improved. It hs een shown lso tht the proposed strtegy llows n operting full pity of the RSC in terms of retive power ompenstion nd tive filtering. Ó 1 Elsevier Ltd. All rights reserved. 1. Introdution Due to its len nd renewle nture, wind energy is eoming one of the importnt renewle soures of energy in the world. Through its ollortion with other renewle soures of energy, suh s solr energy, the world energy rises n e solved in the future [1]. Comprtively with the pst nd due to the progressive integrtion of the nonliner lods in the grid, the prinipl role of WECS is not only to pture the mximum power from the wind ut, lso, to improve the qulity of power [1], Consequently, with the development of the wind frms whih re integrted in the grid, power qulity ould e etter improved in the future. Vrile speed wind genertors re frequently used nd re more ttrtive thn fixed-speed systems euse of their effiient energy prodution, improved power qulity nd dynmi performne during grid fults. Reently, the most of the wind energy onversion systems re equipped with vrile speed DFIG []. Mny works * Corresponding uthor. Tel.: þ ; fx: þ / E-mil ddresses: outout9@yhoo.fr (M. Boutout), mokrni_lkhdr@ hotmil.om (L. Mokrni), mohmed.mhmoum@univ-nntes.fr (M. Mhmoum). re done out power genertion nd power qulity improvement using WECS. In [1,], Gillrd et l., hve studied the grid retive power ompenstion nd tive filtering of the nonliner lods hrmonis y ontrolling the RSC. In this work seletive pss nd filter is used to extrt hrmoni urrent omponents with tking dvntge of the high mplifition effet of the RSC to mitigte hrmoni urrents. In [3], sensorless field oriented ontrol of douly fed indution eletri lterntor/tive filter for WECS ple of simultneously pturing mximum vrile wind power nd improving power qulity y eliminting the most signifint nd troule-some hrmoni urrents of nonliner lods hs een studied. In this ontriution, retive power ompenstion nd over-rting of the RSC re not disussed. In [4], the GSC is used s shunt tive filter in order to ontrol the power ftor nd ensure hrmonis ompenstion. In [5], Jin et l. hve used the GSC s shunt tive filter in stnd-lone grid. In [6], the grid side onverter is tively ontrolled to feed generted power s well s to supply the hrmonis nd retive power demnded y the nonliner lod t the point of ommon oupling (PCC). In [7], Chen et l. hve studied retive power nd hrmoni ompenstion shemes inluding pssive filters, tive filters nd hyrid ompenstion /$ e see front mtter Ó 1 Elsevier Ltd. All rights reserved.

2 M. Boutout et l. / Renewle Energy 5 (13) 378e Nomenlture v Wind speed (m/s) V g PCC voltge (V) i r Rotor urrent (A) i p Liner lod urrent (A) i l Nonliner lod urrent (A) i G Grid urrent (A) ѱ s Sttor flux (W) T em Eletromgneti torque (Nm) T L Turine torque (Nm) P s, Q s Sttor tive (W) nd retive (VAr) powers Q PCC PCC retive power (VAr), L r Sttor nd rotor per phse winding indutne (H) M Mgnetizing indutne (H) R s, R r Sttor nd rotor per phse winding resistne (U) R g Line resistne (U) L g Line indutne (H) C DC us pitor (F) J Totl inerti onstnt (DFIG nd turine) (kg m ) f Totl frition ftor (DFIG nd turine) (Nm s) u s Synhronous ngulr speed (rd/s) u r Rotor ngulr speed (rd/s) u t Turine speed (rd/s) U g DFIG speed (rd/s) d Ger ox rtio R Turine rdius (m) P Pole pirs numer methods for onverter interfed with permnent mgnet genertor sed vrile speed wind turine. In [8], Engelhrdt et l. hve disussed the stedy stte retive power loding pility of DFIG sed WECS y tking into ount the most importnt physil phenomen restriting the retive power supply of DFIG-sed wind turine systems. In [9], Different omintions of retive power ontrol of RSC nd GSC re investigted for DFIG. In [1], Mhmoum et l. hve studied fliker mitigtion in douly fed indution genertor for wind turine system sed on RSC ontrol. In generl, the full pity of the RSC, in terms of tive filtering, hs not een exploited for different operting onditions of the WECS. In this pper, ontrol strtegy is proposed to hieve the filtering full pility of the RSC whih is used to mnge the WECS funtion s priorities, etween prodution of the mximum tive power nd power qulity improvement. The top priority is given to the tive power prodution over power qulity improvement. Then, priority is given to power ftor orretion over hrmonis ompenstion. Finlly, the filtering pility of the RSC is exploited t its mximum (when it is needed) without ny over-rting y using proposed proedure. Moreover, the GSC is ontrolled in suh wy to gurntee smooth DC voltge y using fuzzy logi ontroller. A sinusoidl urrent is ensured etween GSC nd the grid.. Desription nd modelling of the wind energy onversion system The synopti sheme of the studied system is shown in Fig. 1.Itis omposed of WECS, liner lod nd nonliner lod. These elements re oupled together t the PCC..1. Turine model The mehnil power ptured y the turine from the wind is given y the following expression: p t ¼ 1 r pðl; Þsv 3 (1) Where r is the ir density, s is the re of the wind wheel (m ), v is the wind speed (m/s), p (l, ) is the power oeffiient of the turine, l is the tip speed rtio nd is the pith ngle. The tip speed rtio is given y the following eqution: l ¼ Ru t () v Fig. shows the vrition of the power oeffiient versus l for onstnt vlue of the pith ngle. In the se of vrile speed i s i p R p L p Lgging power ftor lod R s P s, Q s TURBINE i g i G PCC P G, Q G GRID R g GEARBOX i r V d R r L r L g i l g DFIG RSC GSC R L L L Non liner lod Fig. 1. Synopti sheme of the studied WECS.

3 38 p pmx M. Boutout et l. / Renewle Energy 5 (13) 378e386 u dr ¼ R r i dr þ L r M didr dt gu s u qr ¼ R r i qr þ L r M diqr dt þ gu s L r M L r M i qr i dr þ g Mu s (1) WECS, one n let u t hnge with the vrition of the wind speed v in order to mintin l t its optiml vlue l opt (see Fig. ), so tht the turine lde n pture the mximum of the wind power... Modelling of the DFIG with sttor field orienttion λ opt Fig.. Power oeffiient versus the tip speed. The DFIG voltge nd flux equtions, expressed in the Prk referene frme, re given y [11]: λ Where u s is the sttor voltge mgnitude ssumed to e onstnt nd g is the slip rnge. Moreover, the sttor tive nd retive powers re expressed y the following equtions: P s ¼ 3 uds i ds þ u qs i qs (11) Q s ¼ 3 uqs i ds u ds i qs (1) Equtions (7.), (7.), (8.) nd (8.) re used to rewrite the sttor tive nd retive powers s follow: P s ¼ 3u sm i qr (13) u ds ¼ R s i ds þ dj ds u s j dt qs u qs ¼ R s i qs þ dj qs þ u s j dt ds u dr ¼ R r i dr þ dj dr dt u qr ¼ R r i qr þ dj qr dt ðu s u r Þj qr þ ðu s u r Þj dr (3) u s Q s ¼ 3 ðu u s Mu s i dr Þ (14) s.3. Rotor side onverter ontrol In this work, the issues whih need to e ddressed y the RSC ontrol re: j ds ¼ i ds þ Mi dr j qs ¼ i qs þ Mi qr j dr ¼ L r i dr þ Mi ds j qr ¼ L r i qr þ Mi qs (4) Moreover, the eletromgneti torque is given y: T em ¼ 1:5p i qs j ds i ds j qs Elsewhere, the mehnil dynmi eqution is expressed s follow: T em ¼ J du g dt þ f U g þ T L (6) The sttor resistne of the DFIG is negleted nd the sttor flux j s is set ligned with the d xis nd ssumed to e onstnt (it is the se of powerful nd stle grid) [1]. Then, one n write j ds ¼ j s nd j qs ¼. Consequently, Equtions (3)e(5) eome respetively in the stedy stte regime: u ds z u s ¼ u qs zu s j s j s ¼ i ds þ Mi dr (5) (7.) (7.) (8.) ¼ i qs þ Mi qr (8.) T em ¼ 3 p M j s i qr (9) Hene, the rotor voltge equtions n e written s follow [13]: -Cpture of mximum energy from the wind (MPPT); -Power qulity improvement, through power ftor enhnement nd hrmonis urrent filtering Mximum power genertion From Eqution (9), one n estlish tht the eletromgneti torque n e ontrolled diretly y ting on i qr urrent omponent. Then, the q-referene rotor urrent is given y: i qrref ¼ u s 3pu s M T emref (15) From Eqution (14), one n note tht the sttor retive power n e ontrolled y ting on i dr. Then, the d-referene rotor urrent is given y: i drref ¼ L s 3u s Q 3u s M u sref (16) s To ensure the MPPT, fuzzy logi speed ontroller (FLC) hs een used (see Fig. 3). Furthermore, to extrt mximum of power from the wind, the genertor speed ommnd is estimted y the following eqution: U gref ¼ d l opt R v (17) With d is the ger ox rtio nd l opt is the optimum tip speed rtio. To ontrol the RSC, the referene i qrref (see Fig. 3) is derived from the speed error e nd its vrition De y tuning the FLC. Also, to ontrol the retive power to desired vlue, ommnd urrent i drref is derived from Eqution (16), s shown in Fig. 3. Elsewhere, to

4 M. Boutout et l. / Renewle Energy 5 (13) 378e Fig. 3. Control sheme of the RSC for power genertion nd hrmoni mitigtion. design the urrent ontrol loops long the two xes, Eqution (1) ws used. The ross oupling terms etween the d-xis nd q-xis n e eliminted y feed forwrd ompenstion. Therey the independent ontrol of the d-xis nd q-xis rotor urrents is relised y dding PI regultor in the loop, s shown in Fig Ative filtering funtion There re vrious methods tht n e used to identify the hrmoni referene urrents. These methods n e essentilly lssified in two prts: the time domin nd the frequeny domin [14e16]. There re lso two possiilities to ontrol the hrmonis in seletive wy. On the one hnd, the desired speifi hrmoni urrents re first seleted nd imposed to urrent ontroller hving lrge ndwidth, nd on the other hnd, seletive urrent ontroller (resonnt urrent ontroller or generlized integrtor) is diretly used to regulte inherently speifi hrmoni omponents [17e]. The most lssil method is lled instntneous power peq theory [14] whih n esily e extended to seletive hrmoni urrent ompenstion. In our se, the instntneous power theory is used s shown in Fig. 4. The resulting deq hrmoni referene urrents i ldh, i lqh re onverted to their equivlent referene rotor urrents i drhref, i qrhref using Equtions (8.) nd (8.). The resulting equtions re: i drhref i qrhref ¼ M i ldh ¼ M i lqh (18) For eing ompensted, the referene deq hrmoni rotor urrents must e tken y n opposite sign of i drhref, i qrhref. So, the resulting hrmoni rotor urrent ommnds tht must e dded to the tive (i qrref ) nd the retive (i drref ) rotor urrent ommnds re given y (see Fig. 3): i drhref 1 ¼ M i ldh i qrhref 1 ¼ M i lqh.4. Power qulity improvement (19) Due to the integrtion of nonliner lods in the grid, the min role of WECS is not only to pture the mximum power from the wind, ut lso to prtiipte in power qulity improvement Ative nd retive power pilities of the RSC To void the over-rting of the RSC during its ontrol for oth MPPT power genertion nd power qulity improvement, it is required to know its tive nd retive powers pilities. By using Equtions (13) And (14), the following expression, whih desries the RSC tive nd retive powers limits, is esily otined: Ps þ Q s þ 3u s 3us M ¼ I u rn () s Fig. 4. Extrtion of the hrmoni omponents with instntneous power lgorithm.

5 38 M. Boutout et l. / Renewle Energy 5 (13) 378e386 Ative power (W) C B Psn A Retive power (VAr) power ompenstion nd hrmoni urrents mitigtion is lulted from the following eqution [1]: qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi I drmx ¼ Irn i (1) qrref In order to exploit the RSC t its mximum pility in terms of power, it is proposed in this pper to express the totl rotor urrent ommnds for tive power prodution, retive power ompenstion nd hrmoni mitigtion y the following equtions: i drtref ¼ i drref þ K i drhref 1 i qrtref ¼ i qrref þ K i qrhref 1 () Where, K is positive gin whih n vry etween nd 1. Then, the seond priority is given to ompenste the retive power over hrmoni mitigtion. Hene, one n write: () First, if the retive rotor ommnd i drref verifies: i drref j I drmx (3) Fig. 5. Power limittions of the RSC. Fig. 5 shows this eqution whih is irle entred t the point C, where I rn nd P sn re respetively the rted rotor urrent nd the rted sttor power. The line AB represents the P s -Q s limittions t the nominl operting point (see Fig. 5)..4.. Mngement of WECS funtion s priorities The pility of the RSC in terms of power is limited y its nominl rotor urrent I rn. The first priority is given to tive power prodution over power qulity improvement. Thus, the mximum vlue of the ville retive rotor urrent to e used for retive Then, the RSC opertes t its full pity in terms of power, nd only tive power prodution nd retive power ompenstion re prtilly possile (i.e. K ¼ ). And the totl rotor urrent ommnds re given y: i drtref ¼ sign i drref I drmx (4) i qrtref ¼ i qrref () Seond, if the retive rotor urrent ommnd i drref verifies: i drref j< I drmx (5) ig -.1Vg is.1vg Fig. 6. Wveforms efore nd fter ompenstion t t ¼. s: ) Grid urrent (i G ) (A) nd PCC voltge (.1V g ) (V), ) Sttor urrent (i s ) (A) nd PCC voltge (.1V g ) (V), ) DC voltge (V).

6 M. Boutout et l. / Renewle Energy 5 (13) 378e Hrmoni RMS (A) Hrmoni RMS (A) Rnk idrtref idr d Rnk iqr iqrtref Fig. 7. Wveforms efore nd fter ompenstion t t ¼. s: ) Grid urrent spetrum efore ompenstion, ) Grid urrent spetrum fter ompenstion, ) d-rotor urrent nd its ommnd, d) q-rotor urrent nd its ommnd. 4 ig 4 is Vg Vg idr d 5 iqr e 15 1 idrtref f 15 1 iqrtref Time (s ) Hrmoni RMS (A) Rnk Hrmoni RMS (A) Rnk Fig. 8. Wveforms efore nd fter ompenstion t t ¼. s under retive sturted rotor urrent ommnd: ) Grid urrent (i G ) (A) nd PCC voltge (.1V g ) (V), ) Sttor urrent (i s ) (A) nd PCC voltge (.1 V g ) (V), ) d-rotor urrent nd its ommnd, d) q-rotor urrent nd its ommnd, e) Grid urrent spetrum efore ompenstion, f) Grid urrent spetrum fter ompenstion.

7 384 M. Boutout et l. / Renewle Energy 5 (13) 378e386 5 idr idrtref iqrtref iqr d idr idrtref iqrtref iqr e 3 irref f 3 irref 1 ir 1 ir Time(s) Time(s) Fig. 9. Wveforms efore nd fter ompenstion t t ¼. s under hrmoni sturted rotor urrent ommnd, ) d-rotor urrent nd its ommnd for the first strtegy, ) q-rotor urrent nd its ommnd for the first strtegy, ) d-rotor urrent nd its ommnd for the seond strtegy, d) q-rotor urrent nd its ommnd for the seond strtegy, e) Instntneous rotor urrent (i r ) (A) nd its referene for the first strtegy, f) Instntneous rotor urrent (i r ) (A) nd its referene for the seond strtegy. Then there is portion of retive rotor urrent to e used for hrmoni filtering. Two ses n e studied: (.1) The first se ours when we hve: i drref þ i drhref 1 þ i qrref þ i qrhref 1 I rn (6) In this se, the RSC n e used for oth retive power ompenstion nd totl hrmoni urrent filtering (i.e. K ¼ 1) without its over-rting. Consequently, the totl rotor urrent ommnds re expressed y the following equtions: i drtref ¼ i drref þ i drhref 1 i qrtref ¼ i qrref þ i qrhref 1 (7) (.) The seond se verifies: i drref þ i drhref 1 þ i qrref þ i qrhref 1 >I rn (8) In this sitution, the RSC n e used to ompenste the totl retive power nd to filter portion of hrmoni urrents without its over-rting. To ovoid ny over-rting of the onverter, two pprohes n e investigted: - In the first strtegy, the hrmoni filtering opertion is omitted (sine the whole of the hrmoni urrents n t e ompensted) nd only the power ftor improvement is onsidered, i.e. the totl d-q rotor urrent ommnds re expressed y Eqution () with K ¼ [1]. In this se, the RSC is not operted t its full pity in terms of tive filtering. - The seond pproh (whih is proposed in this pper), permits to exploit the RSC full pility in terms of power, y filtering portion of hrmoni urrent without ny over-rting. For this purpose, it is proposed to determine n pproprite gin K m ( < K m < 1) whih verifies the following eqution: i drref þ K m i drhref 1 þ i qrref þ K m i qrhref 1 ¼ I rn (9) The physil vlue of K m n e found y solving this seond order eqution. As result, the totl rotor urrent ommnds re expressed s follow: i drtref ¼ i drref þ K m i drhref 1 i qrtref ¼ i qrref þ K m i qrhref 1 (3) In this se, the seletive filtering pproh n e used lso (to mitigte the most dominnt low frequeny hrmonis urrents) [1,3]. 3. Simultion results nd disussion The proposed ontrol strtegy is pplied to WECS equipped with 7.5 kw DFIG. The system prmeters re given in the ppendix. The swithing frequeny of the RSC nd the GSC is hosen equl to 1 khz. The performne of the WECS nillry servies is studied under the nominl sttor tive power

8 M. Boutout et l. / Renewle Energy 5 (13) 378e (P sn ¼ 7.5 kw) for nominl wind speed of 13.3 m/s. The totl lod of the system is omposed of non-liner lod (full ridge diode retifier) nd lgging liner lod (R p L p ) (see Fig. 1) Retive power ompenstion nd hrmoni mitigtion in the se of non-sturted rotor urrent ommnd In this setion, the retive power ompenstion nd hrmoni mitigtion, without sturted rotor urrent ommnds, re studied. The onsidered non-liner lod, oupled t the PCC, hs hrmoni distortion rtio of out 9%, nd the liner lod retive power to e ompensted is of kvar. Figs. 6 nd 7 show the simultion results. The first figure shows the urrents wveforms nd the DC pitor voltge, efore nd fter ompenstion t t ¼. s. The wveforms: grid urrent (i G ), PCC voltge (V g ) nd sttor urrent (i s ) show lerly the performne of the proposed strtegy in terms of power qulity improvement. After ompenstion nd s n e remrked in Fig. 6(), the grid urrent is in phse opposition (genertor mode) with the PCC voltge, Hene unity power ftor hs een hieved t the PCC. The DC pitor voltge is mintined onstnt prtilly t its ommnd vlue of 7 V, y the ontrol of the GSC s shown in Fig. 6(). During tive filtering opertion, one n notie smll osilltions of V d t frequeny of 3 Hz. However, these osilltions do not ffet the DC us stility. As shown in Fig. 7(e), the grid urrent spetrum, efore nd fter tive filtering, prove the enhnement of the grid urrent THD whih is redued from out 9% to 4.7%. Consequently, the RMS of the 5th nd the 7th hrmoni omponents hve een redued from out.71 A to. A nd from.46 A to.37 A respetively. Moreover, the instntneous deq rotor urrents trk dequtely their referenes (see Fig. 7(ed)), in this se of mximum tive power prodution, retive power ompenstion nd hrmoni urrents filtering. 3.. Retive power ompenstion nd hrmoni filtering in the se of sturted rotor urrent ommnd As hs een seen previously (see Setion.4.), the rotor urrent ommnd limit ould e rehed due to the retive power urrent ommnd or to the hrmoni urrent ommnd. Those two situtions of sturted rotor urrent ommnd re studied in the following setions Cse of sturted rotor urrent ommnd due to retive power ompenstion For the rted tive power (P sn ), the mximum vlue of the retive power whih n e ompensted y the DFIG, is out 5 kvar (point B in Fig. 5). To e under the ondition of the sturted rotor urrent ommnd, one n hoose liner lod of retive power of out 9.5 kvar nd non-liner lod s tht of Setion 3.1. Fig. 8 illustrtes the otined simultion results efore nd fter ompenstion t t ¼. s. After ompenstion, the totl rotor qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi urrent ommnds re sturted ( i drtref þ i ¼ 3A) (see qrtref Fig. 8(ed)) for only tive power prodution nd retive power ompenstion. In this sitution, the RSC opertes t its full pity, nd therefore no hrmoni urrents filtering n e hieved without the onverter over-rting. Moreover, only 5 kvar from 9.5 kvar of retive power hs een ompensted. Consequently, the power ftor is improved from out.37 to.63. Elsewhere, from the grid urrent spetrum, shown y Fig. 8(eef), it hs een dedued tht the THD of the grid urrent is inresed from out 6.% to 1.4%. In ft, portion of retive power hs een ompensted without hrmoni filtering, so tht the fundmentl vlue of the grid urrent deresed, nd thus the THD inresed. Note tht, in this se, the RMS of the 5th nd the 7th hrmoni omponents hs remined prtilly the sme, efore nd fter ompenstion, s n e seen in Fig. 8(eef) THD=1.8% 5 THD=18.8% Rnk Rnk d 1 5 THD=1.4% 5 THD=1.33% Rnk Rnk Fig. 1. Grid urrent spetrum efore nd fter ompenstion t t ¼. s under hrmoni sturted rotor urrent ommnd, ) Spetrum efore ompenstion, ) spetrum fter retive power ompenstion only, ) spetrum fter ompenstion using the first strtegy, d) Spetrum fter ompenstion using the seond strtegy.

9 386 M. Boutout et l. / Renewle Energy 5 (13) 378e Cse of sturted rotor urrent ommnd due to hrmoni filtering To show the effetiveness of the proposed strtegy whih permits to exploit the full pility of the RSC in terms of tive filtering, it hs een hosen to ompenste retive power of out 4.5 kvar nd to filter the hrmoni urrents of the sme nonliner lod of Setion 3.1. In this se, the RSC n ompenste the totl retive power euse it is less thn its upper limit (5 kvar). So, portion of.5 kvar is ville nd n e used for tive filtering. This quot of retive power is not enough to ompenste the whole hrmoni urrents without RSC over-rting. In this sitution, s hs een detiled previously (see Setion.4.), two pprohes hve een investigted. Figs. 9 nd 1 show the otined simultion results, efore nd fter ompenstion, in the two ses ) nd ) of Setion.4. respetively. By omprison of the deq rotor urrent omponents of the two strtegies (see Fig. 9(ed)), one n note, when the whole hrmoni urrent n t e ompensted, tht the totl deq rotor urrent ommnds re limited to (i drtref ¼ i drref ¼ 3.4 A, i qrtref ¼ i qrref ¼ A) during out. ms, for the first strtegy. During this time, the hrmoni urrents ompenstion hs not een fully hieved nd the full pity of the onverter hs not een ompletely exploited. In the se of the seond strtegy, nd during the sme time, the deq rotor urrent ommnds re not onstnt nd vry etween 4.17 A nd 4.47 A for i drtref nd etween A nd A for i qrtref. And the optimum gin K m vries etween.99 nd.38, so tht to keep the instntneous rotor urrent lower thn its rted vlue (I rn ¼ 3 A) s shown in Fig. 9(eef) nd ny over-rting of the RSC hs een hppened. During this time, the full pility, in terms of tive filtering, of the RSC hs hieved without RSC over-rting. Consequently, the grid urrent THD hs een redued from 1.8% to 1.4% nd from 1.8% to 1.33% y pplying the first nd the seond strtegy respetively (see Fig. 1(, nd d)). It is to e noted lso tht the grid urrent THD, in the se of simple retive power ompenstion, is out 18.8% (see Fig. 1()). A omprison of the two strtegies urrent THD shows tht n importnt improvement, in terms of hrmoni mitigtion, is hieved y using the seond strtegy. In ft, the enhnement of the grid urrent THD is out.4% for the first strtegy nd.5% for the seond. The signifine nd effetiveness of the proposed ontrol strtegy ppers when the ompenstion of retive power nd tive filtering re rried out y set of wind prk genertors. 4. Conlusion In this pper, novel pproh hs een proposed to mnge nd improve the qulity of the grid power using WECS equipped y DFIG. The RSC is ontrolled in suh wy to mnge etween prodution of mximum tive power nd power qulity improvement without ny over-rting. The proposed priority ontrol lok gives top priority to tive power prodution thn power qulity, nd retive power ompenstion hs priority thn tive filtering. After tive power prodution nd power ftor orretion, the pility of the RSC is fully exploited for tive filtering, without its over-rting; y the lultion of n pproprite portion of rotor urrent ommnds in suh wy to ensure etter filtering qulity nd keep the RSC urrent under its rted vlue. Simultion results prove the effetiveness of the proposed pproh. A seletive filter n e used to ompenste only the fifth nd seventh most dominnt hrmoni urrents, nd gurntee mximum pility of the RSC, in terms of tive filtering, in the sme wy. Appendix Turine prmeters Power (kw) 1 Numer of ldes 3 Turine rdius, R (m) 3 Ger ox rtio 8 DFIG prmeters Power (kw) 7.5 Sttor resistne, R s (U).455 Rotor resistne, R r (U).6 Sttor phse indutne, (H).84 Rotor phse indutne, L r (H).81 Mgnetizing indutne, M (H).78 Genertor inerti, J (kg m ).315 Frition ftor, f (N m s).673 Referenes [1] Gillrd A, Poure P, Sdte S. Retive power ompenstion nd tive filtering pility of WECS with DFIG without ny over-rting. Wind Energy 9;137:63e14. [] Gillrd A, Poure P, Sdte S, Mhmoum M. Vrile speed DFIG wind energy system for power genertion nd hrmoni mitigtion. Renewle Energy 9;346:1545e53. [3] Aolhssni MT, Enjeti P, Toliyt H. Integrted douly fed eletri lterntor/ tive filter (IDEA), vile power qulity solution for wind energy onversion systems. IEEE Trnstions on Energy Conversion 8;3:64e5. [4] Singh M, Chndr A. Applition of dptive network-sed fuzzy inferene system for sensorless ontrol of PMSG-sed wind turine with nonlinerlod-ompenstion pilities. IEEE Trnstions on Power Eletronis 11;61:165e75. [5] Jin AK, Rngnthn VT. Wound rotor indution genertor with sensorless ontrol nd integrted tive filter for feeding nonliner lods in stnd-lone grid. IEEE Trnstions on Industril Eletronis 8;551:18e8. [6] Singh M, Khdkikr V, Chndr A. Grid synhronistion with hrmonis nd retive power ompenstion pility of permnent mgnet synhronous genertor-sed vrile speed wind energy onversion system. IET Power Eletronis 11;41:1e3. [7] Chen Z. Compenstion shemes for SCR onverter in vrile speed wind power systems. IEEE Trnstions on Power Delivery 4;19:813e1. [8] Engelhrdt S, Erlih I, Feltes C, Kretshmnn J, Shewreg F. Retive power pility of wind turines sed on douly fed indution genertors. IEEE Trnstions on Energy Conversion 11;61:364e7. [9] Kyikçi M, Milnovi J. Retive power ontrol strtegies for DFIG-sed plnts. IEEE Trnstions on Energy Conversion 7;:389e96. [1] Mhmoum M, Htoum A, Bououihe T. Fliker mitigtion of douly-fed indution genertor for wind energy onversion system. Mthemtis nd Computers in Simultion 1;81:433e45. [11] Shhzi M, Poore P, Sdte S, Zlghdri MR. Five-leg onverter topology for wind energy onversion system with douly fed indution genertor. Renewle Energy 11;3611:3187e94. [1] Sores O, Gonçlves H, Mrtins A, Crvlho A. Nonliner ontrol of the doulyfed indution genertor in wind power systems. Renewle Energy 1;358: 166e7. [13] Poitiers F, Bououihe T, Mhmoum M. Advned ontrol of douly-fed indution genertor for wind energy onversion. Eletri Power Systems Reserh 9;797:185e96. [14] Akgi H, Knzw Y, Ne A. Instntneous retive power ompenstors omprising swithing devies without storge omponents. IEEE Trnstions on Industril Applitions 1984;3:65e3. [15] Mssoud AM, Finny SJ, Willims BW. Review of hrmoni urrent extrtion tehniques for n tive power filter. IEEE Interntionl Conferene on Hrmonis nd Qulity of Power, Lke Plid (USA) 4:154e9. [16] Bljerg F, Hnsen S, Assiminoei L. Hrmoni detetion methods for tive powerfilter pplitions. IEEEIndustryApplitions Mgzine7;134:e33. [17] Zmood DN, Holmes DG. Sttionry frme hrmoni referene genertion for tive filters systems. IEEE Trnstions on Industry Applitions ;386: 1591e9. [18] Bojoi RI, Griv G, Bostn V, Guerriero M, Frin F, Profumo F. Current ontrol strtegy for power onditioners using sinusoidl signl integrtor in synhronous referene frme. IEEE Trnstions on Power Eletronis 5; 6:14e1. [19] Mttvelli P, Mrfo FP. Repetitive-sed ontrol for seletive hrmoni ompenstion in tive power filters. IEEE Trnstions on Industril Eletronis 4;515:118e4. [] Mhmoum M, Bruynt N. DSP sed ontrol of shunt tive power filters for glol or seletive hrmonis ompenstion, IEEE interntionl onferene on hrmonis nd qulity of power. Orlndo, Florid (USA);. p. 661e666.