ANFIS Based Coordinated Control for an Offshore Wind Farm Connected VSC MTDC System

Transcription

1 ANFIS Bae Coornate Control for an Offhore Wn Farm Connecte VSC MTDC Sytem *M. Ajay Kumar, Member, IEI, B. Vjay Kumar, Member, IEI, N.V. Srkanth, Member, IEEE Department of Electrcal Engneerng Natonal Inttute of Technology Warangal, Ina Abtract: Offhore wn farm are becomng an attractve oluton for wn power n many evelope countre. The voltage ource converter (VSC bae mult-termnal hgh voltage rect current (MTDC tranmon ytem an attractve techncal opton to ntegrate thee offhore wn farm wth the onhore gr ue to t unue performance charactertc an reuce power lo va extrue DC cable. In th paper, an aaptve neuro fuzzy nference ytem (ANFIS bae coornate control egn ha been aree for MTDC ytem n orer to enhance the relablty an to balance the power. A four termnal VSC-MTDC ytem whch cont of an offhore wn farm an ol platform mplemente n MALAB/Smower Sytem oftware. The propoe moel tete uner fferent fault cenaro an mulaton reult how that the novel coornate control egn ha great ynamc tablte an alo the VSC-MTDC ytem can upply Ac voltage of goo ualty to offhore loa urng the turbance. Keywor ANFIS; Coornate controller; Offhore wn; MTDC; MATLAB; VSC HVDC. publcaton ext n the area of VSC bae MTDC. All thee reearch work concentrate on fferent apect uch a DC fault locaton an protecton of MTDC [6], control methoologe [5], [7], an alo moelng of MTDC [8]. MTDC ytem for power tranmon between conventonal network an DFIG bae wn farm were ecrbe n [4], [9]. In [], a three termnal VSC bae HVDC ytem connectng onhore gr to two offhore wn farm wa ntrouce an analyze. Recently, a four termnal MTDC ytem wa evelope [] where two onhore gr locate at fferent geographcal area were ntegrate by two offhore wn farm an the DC gr control trategy an power harng were clearly epcte. However, a far a control of MTDC ytem concerne, the reearch wa contrane to the conventonal coornate control egn []. In th paper, an ntellgent coornate controller (ANFIS bae mplemente for the frt tme n MTDC ytem, whch gve fat repone an goo ualty of upply to offhore platform wthout any mathematcal moelng. I. INTRODUCTION In recent year, renewable energy ource are becomng more popular for proucng electrcal power. Among them, wn energy ha become one of the foremot economcal an both envronmentally an techncally attractve opton []. Wn ntallaton have up to now nvolve largely on-lan te. However, wn potental eem to ext alo n offhore, where there an avantage of hgher wn conton an fewer envronmental retrcton, although the avantage of more ffcult acce an hgher ntallaton an mantenance cot mut be taken nto account []. Offhore wn farm are often connecte to the man gr va hgh voltage rect current (HVDC tranmon technology. Nowaay, wth the growth n HVDC tranmon, voltage ource converter HVDC (VSC HVDC alo known a HVDC Lght tranmon ytem ha become more an more mportant n the larger nterconnecte power ytem []. The man avantage of HVDC Lght over conventonal HVDC that the extenon to mult-termnal DC (MTDC ytem relatvely eay an hence, the applcaton of MTDC ytem becomng more attractve than before. The VSC bae MTDC ytem better than the two-termnal HVDC ytem n everal apect lke relablty, control, flexblty an economc [4]-[5]. One eental applcaton of VSC bae MTDC tranmon ytem to nterconnect offhore wn farm an ol/ga platform to the onhore gr, whch wll reuce the operatonal cot an ncreae the relablty. Although, very few number of VSC bae MTDC ytem ntalle o far, a large number of II. MTDC SYSTEM MODEL The mult-termnal VSC bae HVDC ytem tete n th paper hown n Fg.. It cont of four termnal, one termnal (VSC connecte to the conventonal power plant feeng power va VSC to a trong gr locate at cty center through HVDC Lght tranmon ytem, the thr termnal (VSC connecte to an offhore DFIG bae wn farm tranmttng power to the onhore gr va DC cable an fourth converter (VSC4 lnk to the offhore platform upplyng power from the lnk. Flter Flter Flter Flter Fg. MTDC ytem for offhore wn farm an ol platform nterconnecton The man objectve of controllng MTDC ytem not only to mprove the overall performance of the ytem, but alo to protect the eupment whch n ervce. VSC play a vtal role n the afe operaton of the MTDC ytem. DC Cable (5km /4/$. 4 IEEE

2 VSC control the actve power an reactve power where a VSC aopt a DC voltage control metho. But the wn farm e converter VSC mut ue contant actve power an voltage, ung power nepenent control ytem. Fnally, the converter connecte to an ol platform (VSC4 aopte wth voltage control metho n orer to prove unnterrupte an balance voltage at the termnal. Each VSC of the four termnal MTDC ytem couple wth network va lne retor R, phae reactor L an a DC capactor C n parallel to the DC bu from the taton a hown n Fg.. The followng euaton are obtane n the - ynchronou frame []. Fg.. Control tructure of a converter V Vc = L + R + ω L ( t V Vc = L + R ωl ( t Where V an V are ource voltage, an are lne current, V c an V c are converter nput voltage. Bae on the ntantaneou power theory, neglectng the loe of the converter an the tranformer, the actve an reactve power exchange from the en of the DC lnk are: ac = (V + V ( = ac (V - V (4 Suppoe, the recton of the ource voltage vector a -ax, V =. So ( an (4 can be re-wrtten a: ac = V (5 ac = V (6 Snce V contant, from (5 an (6 t clear that the actve power wll be controlle by, whole the reactve power wll be controlle by. On the DC e of the converter, DC current an DC power are; v = (7 t C + c = V (8 Where the DC current to be followe by the capactor, v the DC lnk voltage an c the current on the DC cable. Neglectng the lo of converter, power of e eual to the DC e. V ac = (9 = V ( Bae on the law of conervaton of energy, the actve power tranferre n the MTDC ytem mut atfy the followng euaton: = ( In MTDC ytem, each VSC controlle by local controller an the whole ytem coornate by the mater controller. Now, the control methoologe of MTDC ytem are bly cue a follow: A. Outer Controller In general, contant actve, reactve power control or contant /DC voltage control trategy can be aopte for local control at each VSC n MTDC ytem. Control crcut of VSC hown n Fg. cont of an outer control loop an nner current control loop. The outer controller nclue the actve, reactve power control, DC voltage control an an voltage controller. The choce among thee controller wll epen on the applcaton. The outer controller wll calculate the erence value of the converter current. From the euaton (5 an (6, t clear that every converter can control t actve an reactve power nepenently. A combnaton of an open loop an I controller ue to keep the actve power to t ere value, gven by the euaton: _ = v K + (Kp + ( ( Smlarly, reactve power can alo be controlle a n the prevou cae by combnng the I controller a hown n below. _ = v K + (Kp + ( ( In general, the voltage controller choen at nverter taton locate on offhore ol platform o a to obtan an unnterrupte an balance voltage from the voltage controller, the -ax current erence can be obtane ung the euaton Wth K = (Kp + (v _ v v = (v + v = v K = (Kp + (v _ v (4 (5 MTDC ytem houl mantan a contant DC lnk voltage uner normal conton n orer to atfy the power balance euaton. When the MTDC ytem actve power uper flow, VSC en back to the gr an n th way wthout any

3 energy torage evce, VSC act a an energy buffer by encounterng the wtchng loe an tranmon loe. When a I controller ue, the DC current erence of VSC can be wrtten a _ = ( K p K + ( v _ v (6 All thee outer loop I regulator calculate the erence value of the converter current vector (I _, whch the nput to the nner current loop. B. Inner Current Controller Accorng to the euaton ( an (, the current of an ax can be controlle by V c an V c repectvely. The Inner current loop block contan two I regulator that wll calculate the erence value of the converter voltage vector (V -. By ung clarke tranformaton V - tranforme nto V -abc, whch the nput to the pace vector pule wth moulaton block. C. ANFIS bae Coornate Controller MTDC Structure more complex ue to the nterconnecton of more than two converter for the ame DC bu. So t neceary to control the DC lnk voltage wthn acceptable lmt to aure that all actve power on the DC gr tranmtte nto the gr/loa. In orer to enure the tablty an relablty of the MTDC ytem, ANFIS bae coornate control trategy ntrouce n th paper. ANFIS an aaptve network that functonally euvalent to a fuzzy nference ytem, where the output ha been obtane by ung fuzzy rule on nput. Fg. epct a two - nput one - output ANFIS tructure [4]. The two nput are x (error whch wa obtane a (V _ ~V, x (change of error an the output a controlle DC lnk voltage. Each nput an output varable ha fve lngutc varable,.e Negatve large (NL, Negatve mall (NS, Zero (Z, otve mall (S an otve large (L. Hence, n th propoe ANFIS controller total 5 lngutc varable for the output are employe. Fg.. A Fve layer ANFIS tructure The propoe ANFIS archtecture cont of fve layer wheren crcle hape noe are calle fxe noe, whch mean the noe parameter are nepenent on the other noe an uare hape noe are calle aaptve noe, whoe noe parameter epen on the other noe. Each neuron n the frt layer correpon to a lngutc varable whle the output eual the memberhp functon of th lngutc varable. In the econ layer, each noe multple the ncomng gnal an en out the prouct that repreent the frng trength of a rule. Each noe n the thr layer etmate the rato of the rule frng trength to um of the frng trength of all rule. In the fourth layer, the output the prouct of the prevouly foun relatve frng trength of the th rule. The fnal layer compute the overall output a the ummaton of the ncomng gnal. The propoe controller checke n MATLAB/ANFIS etor tool box wth a trangular memberhp functon a t offer mnmum tranng error. Snce, the back propagaton algorthm notorou for t lowne an tenency to become trappe n local mnma, a hybr learnng algorthm ue n th contrbuton. Th algorthm fat an accurate n entfyng the parameter. The parameter of the ANFIS controller are gven n Table. TABLE.. ANFIS ARAMETERS Number of noe 75 Number of lnear parameter 75 Number of nonlnear parameter Total number of parameter 5 Number of tranng ata par 6 Number of tetng ata par Number of fuzzy rule 5 III. SIMULATION AND RESULT ANALYSIS In the tet ytem a hown n Fg., offhore wn farm cont of unt of DFIG; each one ha a nomnal power ratng of.5 MW, theore the total capacty of MW. The onhore gr moele a MVA, kv voltage ource. The offhore platform moele a a pave loa of MW. The Tet ytem wa mplemente n MATLAB/ Smulnk an three cae tue were carre out to emontrate the feablty of the controller uch a a three phae to groun fault on the gr e termnal, change n wn pee, an a three phae fault at the offhore platform. Snce, the fault on the ac e of VSC oe not prouce a etructve voltage urge an poe a great threat to the ytem tablty; only the mulaton reult aocate wth an ac fault on the nverter e are preente. The ynamc repone of actve power, reactve power, voltage an current at all the termnal for fferent perturbaton are hown n Fg A. Three hae fault at an gr (Near VSC A balance three phae fault wa apple on ac gr e at 4 for 5 cycle uraton to oberve the effect of the propoe controller an mulaton reult were hown n Fg. 4. It clear from the Fg. 4(a to ( that, actve power an reactve power were uckly able to track ther pre-efne value after removng the fault at an gr an urng the fault there a poblty of power tranfer at all the VSC expect VSC. Irrepectve of the fault, the offhore wn farm generatng t rate power of MW at a contant wn pee of m/ a epcte n Fg. 4(e.The DC lnk voltage of MTDC ytem an power avalable at the DC e of the VSC are hown n Fg. 4(f. Here, one can oberve that the DC power tranferre through VSC urng the fault zero an after the fault cleare at 4., the VSC move out of the current lmt control moe an the DC lnk voltage ocllaton were reuce n m.

4 Actve power, (pu Reactve power, (pu (a Actve power (pu Reactve power, (pu (b Actve power, (pu -. Reactve power, (pu -.5 (c Actve power (pu Reactve power, (pu. -. ( (MW (Mvar 5-5 V (V 5 Wn Spee (m/ x (e V (V DC ower (pu +V -V VSC VSC VSC VSC4 (f Fg. 4 Dynamc of (a VSC (b VSC (c VSC ( VSC4 (e Wn farm an (f DC lnk parameter of MTDC ytem for a -phae fault at onhore ac gr wth a uraton of 5 cycle. B. Change n wn pee The econ cae tuy bae on the operaton wth change n the wn pee at that offhore power plant, an the reult are hown n Fg.5. Intally, the wn pee m/ wth generate power beng aroun MW from the DFIG wn farm. When the wn pee ha been ecreae graually from m/ to m/ an agan et to m/ a hown n Fg.5(f, the wn power generate alo change from MW to 4 MW an accorngly. A the VSC can balance ± MW fluctuaton, rrepectve of change n wn pee the actve power an reactve power at all the termnal are mooth an able to track ther erence value a hown n Fg.5(a to ( an DC power balance can be oberve from Fg. 5(e repectvely. Actve power, (pu.9 Reactve power, (pu. -. (a

5 Actve power (pu Reactve power, (pu (b Actve power, (pu.8.7 Reactve power, (pu -. Actve power (pu -.5 Reactve power, (pu -. (c ( (MW 5 (Mvar V (V 5 Wn Spee(m/ (f Fg. 5. Dynamc of (a VSC (b VSC (c VSC ( VSC4 (e DC power an (f Wn farm parameter of MTDC ytem for a change n wn pee Actve power, (pu Reactve power, (pu Actve power (pu (a Reactve power, (pu (b (pu VSC VSC VSC4 VSC (e Actve power, (pu.8.6 Reactve power, (pu (c

6 Actve power (pu Reactve power, (pu x 5 V (V + V - V DC ower (pu VSC VSC.5 ( (e tch_eg (MW - (Mv ar -4 V (V 5 (g Fg. 6 Dynamc of (a VSC (b VSC (c VSC ( VSC4 (e DC lnk (f ptch angle an (g Wn farm parameter of MTDC ytem for a -phae fault at offhore ol platform wth a uraton of 5 cycle. C. Three hae fault at an Offhore latform (Near VSC4 The lat cae oberve wa a three phae hort crcut fault at the offhore platform for the uraton of 5 cycle, an the mulaton reult were hown n Fg. 6. Before fault, power tranferre from conventonal power plant an offhore wn farm to the gr an offhore platform moothly an urng the fault, the power tranfer to offhore loa zero an at the remanng termnal power hare n uch a way to get the power balance a hown n Fg. 6(a to (. It clearly emontrate n Fg. 6(e that, the DC lnk voltage of MTDC ytem ha mnmum ocllaton when compare to a fault at gr an after clearng the fault, VSC control the DC voltage an other converter control the actve power hence, the ytem wll reach t normal tate mmeately. The wn farm ynamc can be oberve n Fg. 6(f an (g where the ptch angle, wn power an DC voltage of the wn farm converter are table rrepectve of the fault at offhore platform. Even uner uch large perturbaton, the MTDC ytem contnue to operate moothly n accorance wth the pre-efne tanar. (f VSC VSC4 IV. CONCLUSIONS In th paper, ANFIS bae coornate control trategy ha been attemte for MTDC ytem ealng wth offhore VSC an onhore VSC at fferent perturbaton. The mulaton reult uner normal conton how that the coornate control trategy keep voltage RMS contant, tranmt the power from wn farm to gr an offhore ol platform va DC lne. Smlarly, for large perturbaton at an gr/ offhore platform, the MTDC ytem repon uckly an then each controlle output return to t pre-efne value mmeately. Another avantage of MTDC ytem operaton n ntegratng offhore wn farm to the onhore gr that, when part of the ytem are eparate ue to varou reaon, the ytem contnue to operate n table regon. REFERENCES [] Leon Frer, an Dav Infel, Reneawable energy n power ytem, It e.. John Wley & Son, Lt, UK, 8. []. Breet, W. L. Klng, R. L. Henrk, an R. Valat, HVDC connecton of offhore wn farm to the tranmon ytem, IEEE Tran. Energy Conv., vol., no., pp. 7 4, Mar. 7. [] M. Ajay kumar, K. U. Archana, an N. V. Srkanth, HVDC Lght Sytem: An overvew, Internatonal Revew on Moellng an Smulaton, Vol. 5, No. 5, pp.95959, October. [4] W. Lu an B.T. Oo, remum ualty power park bae on multtermnal hv, IEEE Tranacton on ower Delvery, vol., no., pp , Aprl 5. [5] T. D.Vron, X.I.Koutva, an G.B.Gannakopoulo, Control of an HVDC lnk connectng a wn farm to the gr for fault re-through enhancement, IEEE Tranacton on power ytem, Vol, no.4, pp. 9 47, November 7. [6] L. Tang an B.T. Oo, rotecton of VSC-mult-termnal HVDC agant DC fault, n IEEE Annual ower Electronc Specalt Conference, vol., pp ,. [7] C. Harong, W. Chao, Z. Fan, an. Wulue, Control trategy reearch of VSC bae multtermnal HVDC ytem, n IEEE ES ower Sytem Conference an Expoton, pp , 6. [8] S. Cole, J. Beerten an R. Belman "Generalze ynamc VSC MTDC moel for power ytem tablty tue", IEEE Tran. ower Syt., vol. 5, no., pp ,. [9] M. Ajay kumar, K. U. Archana, an N. V. Srkanth, Fat Fault Recovery of a Gr Integrate Wn Farm Bae HVDC Lght Tranmon Sytem, n. proc. IEEE/ES Innovatve mart gr technologe conference, Kuala Lampur, pp.-6, 4. [] Lng Xu,Lnglng Fan,an Zhxn Mao, Moelng an Smulaton of Mult-Termnal HVDC for Wn ower Delvery, n proc. IEEE ower Electronc an Machne n Wn Applcaton, pp.-6,. [] X. Le, Y. Langzhong an M. Bazargan "DC gr management of a mult-termnal HVDCtranmon ytem for large offhore wn farm", n roc.int. Conf. Sutanable ower Generaton an Supply, pp [] C. Derckxena, et al, A trbute DC voltage control metho for VSC MTDC ytem, Electrc ower Sytem Reearch, Vol. 8, pp ,. [] M. Ajay kumar, an N. V. Srkanth, erformance of SVWM bae vector controlle HVDC Lght tranmon ytem uner balance fault conton, n proc. of IEEE power an energy conference at Illno, USA, (Feb. -,,, pp [4] M. Ajay kumar, an N. V. Srkanth, An aaptve neuro fuzzy nference ytem controlle pace vector pule wth moulaton bae HVDC lght tranmon ytem uner fault conton, Central European Journal of Engneerng, Sprnger, Vol.4. No.,.7-8, March. 4.