Speed Sensorless Control of DFIG Based MRAS Observer

Transcription

1 Proceeing of the 14 th International Mile Eat Power Sytem Conference (MEPCON 1), Cairo Univerity, Egypt, December 19-21, 21, Paper ID 21. Spee Senorle Control of DFIG Bae MRAS Oberver Ahma Amar Naaani an Abulkaer Ghazal Abulkaer Joukhaar Abel latif El Shafei Department of Electrical Drive Department of Mechatronic Department of electric power an machine Univerity of Aleppo Univerity of Aleppo Cairo Univerity Aleppo, Syria Aleppo, Syria Giza, Egypt Abtract - The Doubly Fe Inuction Generator (DFIG) with back-to-back four-quarant power converter i coniere a the main prototype ue with win power converion ytem. Thi paper aim to eign a control algorithm uing hyterei controller to control the rotor an the gri ie converter an manage active an reactive power exchange between the generator an the gri. MRAS oberver i propoe for DFIG pee etimation. Simulation reult have been conucte from the propoe DFIG control ytem an oberver, the obtaine reult confirm the accuracy an valiity of propoe control trategy. It ha alo hown that the propoe etimation i robut againt R r an R mimatch. Inex Term - oubly fe inuction generator, hyterei controller, GSC, RSC, MRAS Oberver. I. INTRODUCTION Win power energy i one of the mot favourable ource of clean an renewable energy that can partially olve the energy an environment ilemma we are facing toay. For example, win power converion ytem can reuce the emiion of CO 2 an other harmful gae. A 1-MW win power generator reuce 2 ton CO 2, 1 ton SO2 an 6 ton of NO 2 emiion to the atmophere [1]. Therefore, win energy i alway known a blue ky anthracite. Every year, many win farm employ win turbine bae on the DFIG technology. Thi machine ha a big attention in Variable Spee Contant Frequency (VSCF) power Converion Sytem. Compare to the ynchronou generator bae win generation technology, the DFIG bae win generation technology ha everal avantage, uch a fourquarant active an reactive power capabilitie, lower converter cot an lower power loe, the capacity of the upplie excitation power i only 25%~3% of the whole power unit [2]. Thi paper icue the control of rotor-ie converter (RSC) to implement the power control of the DFIG connecte to a utility power gri uing hyterei type controller; the control trategy for Gri Sie Converter (GSC). So that unity power factor an regulate DC bu voltage are achieve. A chematic iagram of a DFIG-bae win energy converion ytem i hown in Fig. 1. The propoe DFIG control ytem work in enorle pee moe of operation. An MRAS oberver i propoe to etimate the generator haft pee. II. DFIG MATHEMATIC MODEL A oubly fe inuction machine i a woun rotor with back-back converter in the rotor circuit. A DFIG work a a generator or a a motor at both above an below the ynchronou pee by controlling the power injecte into the rotor. In DFIG the rotor i upplie by PWM inverter, while the tator i irectly connecte to gri. The rotor current exciting frequency i controlle a the win velocity i change. The frequency of output power i fixe at gri frequency, which i given a follow: ω = p Ωm ± ωr (1) Where ω i the gri electrical angular pee, Ω m i the mechanical angular rotor pee, ω r i the electrical angular pee of rotor variable, an p i the number of pole pair. In ubynchronou operation moe the ign in (1) i poitive, otherwie it i negative in uperynchronou operation moe. Equation (1) etablihe i the bai for VSCF. The mathematical equation of the DFIG in term of tator, rotor voltage an flux are given a follow [3]: V = Ri ω Φq + Φ (2) V q = R iq + ω Φ + Φq (3) V r = R rir ( ω ω)φ rq + Φr (4) V = R i + ( ω ω)φ + Φ (5) rq r rq r The irect an quarature tator an rotor flux component are given a follow [4]: Φ Li + Lmir = (6) Φ q Liq + Lmirq = (7) rq 476

2 P Q P r Tmech Ωm ω Tem Fig. 1 Main layout of DFIG ytem Φ r Lrir + Lmi = (8) Φ rq = Lrirq + Lmiq (9) The -q teay-tate equivalent circuit of the DFIG i epicte in Fig. 2 [5]. V R Φ L L m R r jωφ jωrφr Fig. 2 Equivalent of DFIG in ynchronou reference frame III. ROTOR SIDE CONVERTER CONTROL ALGORETHIM Vector control i the mot popular cheme for the inepenent control of the active an reactive power output of the DFIG rive. Thi technique ha many avantage compare to other trategie; it make the control algorithm imple, robut an provie fat repone. Auming the DFIG i connecte to the tate power gri in which the gri voltage an frequency i contant. Fixing the -axi of the ynchronou frame on the tator voltage vector, a tator voltage oriente (SVO) control i obtaine. Thu, the vector of the tator voltage i: V = V + j (1) Accoring to (1), the active an reactive power output from the tator ie of the DFIG can be repreente a: P = V i (11) Q Viq = (12) Subtituting (2) in (11) an (3) in (12) repectively, the active an reactive power can be erive a follow: V ( Φ Lmir ) P = (13) L Lr Φr Vr Q V ( Φq Lmirq ) = (14) L A een from (13) an (14), the active an reactive power are relate to rotor current i r an i rq repectively. Therefore, the active an reactive power can be controlle via i r an i rq repectively, which i poible through the control of v r an v rq. In general, it i preferre to replace i r _ ref an i rq _ ref by P _ ref an Q _ ref repectively. So the propoe control cheme i hown in Fig. 3 i r _ ref v P _ ref equ (18) r DFIG Q _ ref equ (19) irq _ ref Control Unit Fig. 3 Prototype of rotor current etimator Bae on the above icuion, a rotor current mut be regulate to get the require power. Hyterei type controller i propoe ue to it fater ynamic repone, goo accuracy, high robutne an impler tructure compare to the conventional proportional-integral controller [6]. The propoe control algorithm aume converting the two reference ignal i r _ ref an i rq _ ref uing Park tranformation invere into abc reference frame, then by comparing the three rotor current ignal i ra _ ref, irb _ ref an irc _ ref with actual rotor current. The error ignal iue from comparion are applie to hyterei controller. The logical output of thee controller are the witching ignal of power tranitor in RSC. The propoe algorithm bae on hyterei controller i hown in Fig

3 P _ ref i r _ ref equ (18) i Q rq _ ref _ ref equ (19) ωˆ θˆ,q a,b,c MRAS Oberver i ra _ ref +_ i rb _ ref i rc _ ref +_ +_ Fig. 4 Propoe rive algorithm for RSC _ Gri VI. Gri Sie Converter (GSC) CONTROL ALGORITHM V c + DFIG A. Park GSC Moel Figure 5 how a GSC (PWM rectifier). The goal of the control ytem i to maintain the DC-bu voltage to the require level for RSC, while the main input current houl be inuoial an in phae with their counterpart voltage, for which the control ytem of DFIG maintain unity power factor conition [7]. V a V b V c R rec R rec R rec L rec L rec L rec i a i b i c T T 1 3 T5 T 2 e a T 4 e b T 6 Fig. 5 Structure of GSC e c i1 i2 For moelling an control eign, the -q ynchronou frame voltage component are [8]: V = e + Lrec i + R rec i ω Lrec iq (15) V q = eq + Lrec iq + R rec iq + ω Lrec i (16) Where R rec an L rec are reitance an inuctance of boot inuctor, repectively. B. GSC Control Algorithm The propoe algorithm of GSC aopt the SVO technique to regulate DC-Link voltage an achieve a unity power factor. Thi trategy lea to getting the following active an reactive power: P = V i (17) rec Qrec V iq = (18) C i c Vc Rotor Sie Converter Thu, the current comman of q-axi control the reactive power an it i obviou that the current comman of q-axi mut be zero i q _ref = for unity power factor operation. Wherea a current comman of -axi control the active power, an conequently control inirectly the DC-link voltage. From the above mentione analyi, the - axi mut have two loop; inner one, which employe hyterei controller to regulate the -axi current; the outer loop; which ue proportional-integral controller to control the DC-bu voltage. The output of the PI controller generate i _ref. The reference -axi current, which i forme by PI controller an q-axi current, which et to zero are both tranforme to abc reference frame uing the Park tranformation invere. The error ignal iue from the comparion between current reference value an actual one are applie to hyterei controller. The logical output of thee controller are the witching ignal of power tranitor in GSC to maintain the eire current. The propoe cheme i hown in fig. 6. V c V c _ref i q _ref = i _ref i q _ref θ,q a,b,c i ra _ ref i rb _ ref i rc _ ref Fig. 6 Propoe rive algorithm for GSC V. MRAS OBSERVER From fig. 4, in DFIG control ytem information about the machine rotor pee i ignificant for high ynamic performance operation. The rotor pee ignal can be obtaine by everal metho e.g., pee enor or uing imple open loop pee etimator. Both have many rawback, the firt metho ha a problem in mechanical coupling an coty ue to ue a enor an cable. While in open loop etimator the accuracy of pee etimation epen trongly on machine parameter [9]. Thi paper propoe an MRAS bae pee etimation robut againt parameter mimatch R r an R variation. The propoe oberver i bae on comparion of two ignal the firt come from a Moel Reference (MR) block, which i inepenent from pee value, wherea the econ i obtaine from Aaptive Sytem (AS) which inclue pee value. The error ignal between MR an AS i applie to Aaptation Mechanim (AM). The output of the AM i a tuning ignal ue to ajut the AS for which the 478

4 error i minimize. Fig 7 how a block iagram of an MRAS oberver. χ Q e χ Q ω Fig. 7 Prototype of MRAS oberver In fig. 7 χ repreent the reference variable an χˆ i an etimation of χ an ωˆ i etimate rotational pee. In thi paper two approache are icue; the firt one epen on the active power moel. Equation (19) how the moel reference of the active power which i erive uing the rotor current an voltage in αβ reference frame which inepenent from the etimate quantity. However; the ajutable moel i erive uing the rotor current an flux in αβ reference frame a hown in (2). A een from (2) the ajutable moel relie on the etimate rotor pee P r = Vrα + Vrβ (19) Pˆ R (i2 i2 r = r rα + ) ˆ rβ + ω(φrβ Φrα ) + (2) Φ Φ rα rβ + The error ignal between the MR an AS i riven to zero uing a PI-type aaption mechanim in which the tuning pee ignal i converge to it true value. In pite of, it implicity an eae of implementation it, however, uffer from being affecte by rotor reitance uncertainity, which may caue a pee etimation error an poible pee ivergence. To eliminate the above mention rawback the reactive power moel i propoe. In thi cheme the MR an AS moel are a given: Qr = Vrβ Vrα (21) Φrβ Φ Qˆ r = ωˆ ( Φrα Φrβ ) + rα (22) Equation (22) how the Aaptive Sytem moel which i inepenent of the rotor reitance. Thi lea to higher accuracy of the pee etimation regarle any variation in rotor reitance. The propoe MRAS oberver cheme i hown in Fig. 8. The rotor flux component Φrα, Φrβ in (22) have been obtaine uing (8) an (9). VI. SIMULATION RESULTS To valiate the propoe control trategy with the pee etimation approach, the inter ytem e.g., the DFIG control ytem with MRAS-bae pee etimation ha been built in MATLAB/SIMULINK. The DFIG parameter are given in appenix I. ω Fig. 8 Propoe MRAS cheme for rotor pee etimation It ha been aume that the DFIG control ytem i place in ieal conition an the win velocity provie rotational pee of 22 ra/ec. Then, it i impoe an active power reference of -1W an a reactive power reference et zero VAR. The rotational pee i increae up to 48 ra/ec within three econ a hown in fig. 9. In aition to, the rotor reitance ha been change uring the tet graually from ( Ω ) in an attempt to check reliability of the propoe rive algorithm. The aim i to invetigate controller an etimator robutne veru parameter uncertainty. The following iagram how the conucte reult obtaine from the evelope DFIG control ytem. In which the DFIG ytem i connecte to gri with 5 Hz. Fig. 9 how that the etimate pee coincie with the actual rotational pee. Rotor Spee (ra/ec) Actual pee Etimate pee Time (Sec) Fig. 9 Actual an etimate rotor pee It i een in Fig. 1 an Fig. 11 that the active an reactive power are tracking their correponing reference ignal, epite the imultaneou changing in variable tate an ytem parameter. The DC-link current can be expree a a function of the rotor current an the witche tate a follow [7]: I_Inv = Ta ia + Tb ib + Tc ic (23) Ignoring the power loe acro the tator an rotor reitance, the rotor active power can be expree a the active power elivere to the rotor by the 4-quarant converter, the mechanical power elivere to the haft of the generator can be calculate a follow [1]: P r = SP (24) Pmech = (1 S) P (25) 479

5 Stator Active Power (w) Rotor Active Power (w) Stator Reactive Power (VAR) Fig. 1 Stator active power repone Fig. 11 Repone of tator reactive power The irection of inverter current i correponing to DFIG tatu, if, for intance, the machine work in ubynchronou pee the inuction machine aborb current from the gri an vice vera for over ynchronou pee. Fig. 13 how the inverter current Fig. 13 Repone of rotor active power When the pee change from ub-ynchronou operation to uper-ynchronou operation, the phae hift in αβ current variable i revere, a hown in Fig. 14. Rotor Current (Amp) Time (Sec) Fig. 14 Rotor current Fig. 15 how a Fourier analyi for PWM- rectifier, current an it i obviou that the current i inuoial ue to the abence of the lower orer an higher orer a harmonic. Inverter Current (Amp) Time (Sec) Fig. 12 Inverter current Equation (24) an (25) ecribe clearly the power flow in the DFIG for over-ynchronou an uner-ynchronou operation. During over ynchronou pee the 4-quarant converter eliver active power to the gri. In uner ynchronou pee, the 4-quarant converter aborb active power from the gri an inject it into DFIG rotor ie. Fig. 13 how the rotor active power. Fig. 15 Fourier analyi for GSC current The goo performance of control algorithm of PWM rectifier appear in fig. 16. The output voltage catche the reference ignal, regarle an amplitue an the irection of the output current of the PWM rectifier. 48

6 PWM Rectifier Output (Volt) Fig. 16 DC Bu voltage Fig. 17 how q current of GSC, where i q _ref =, which mean the performance of control trategy i goo an the ytem achieve unity power factor. PWM Rectifier current (Amp) axi current q-axi current Fig. 17 PWM rectifier current VII. CONCLUSION In thi paper, a new control trategy ha been evelope for win energy tranmutation ytem control. The propoe control algorithm aopt hyterei controller to control Rotor Sie Converter (PWM Inverter) an manage the injecte power into gri utility. In aition, the preent reearch work i focue on the eign of gri ie converter an the control algorithm to achieve the require DC-Bu voltage, an get unity power factor. Hyterei controller ha been ue in thi paper thank to characterize by many avantage; e.g., no nee for PWM moulater; ha fat ynamic repone an robut againt parameter uncertainty referring to Fig. 1 an Fig.11. It ha been alo evelope a new pee etimation uing MRAS-Bae approach. It i, however, been claime that the propoe MRAS oberver robut againt R r an R variation. GSC an RSC control algorithm have been eigne bae on Stator Voltage Orientation, in which full ecoupling control i provie. Full ytem (DFIG, GSC, RSC an MRAS oberver) ha been built uing Matlab-Simulink. an tete for full loae an ( 3% ± of ynchronou pee) in three econ. Reliability, fat repone an robut have been valiate uring the imulation tet. Appenix I Double Fe Inuction Generator Parameter P N 1 Watt L.28 Henry R 7.2 Ohm R r 1.35 Ohm L m.118 Henry L r.75 Henry Number of pole pair 4 - REFERENCES [1] F. Xiaoxu, L. Yuegang, B. Yan, X Daping, Moeling an Simulation of the Variable-frequency Excitation Power Supply Serve for the Win Power DFIG IEEE, pp [2] X. Yu, Z. Jiang, Y. Zhang, 28 A Synergetic Control Approach to Gri-Connecte Win-Turbine Doubly-Fe Inuction Generator IEEE, pp [3] Z. Jiang, X. Yu, 29 Moeling an Control of an Integrate Win Power Generation an Energy Storage Sytem IEEE, 8. [4] T. Ghennam, E.M.Berkouk,, B.Françoi, 29 Moeling an Control of a Doubly Fe Inuction Generator (DFIG) Bae Win Converion Sytem IEEE, pp [5] S. Chonrogianni, M. Barne, 28 Stability of oubly-fe inuction generator uner tator voltage orientate vector control IET Renew. Power Gener., Vol. 2, No. 3, pp [6] M. Malinowki, 21 Senorle Control Strategie for Three - Phae PWM Rectifier Ph.D. Thei, Waraw Univerity of Technology, 127. [7] W. Jiuhe, Y. Hongren, Z. Jinlong, L. Huae, 26 Stuy on Power Decoupling Control of Three Phae Voltage Source PWM Rectifier IEEE, China. [8] J. Liao, S. Yeh, 2 A Novel Intantaneou Power Control Strategy an Analytic Moel for Integrate Rectifier/Inverter Sytem IEEE, pp [9] P. Va, Senorle Vector An Direct Torque Control, Oxfor Univerity pre,95. [1] S. Müller, M. Deicke, W. De Doncker, 2 Ajutable Spee Generator for Win Turbine bae on Doubly-fe Inuction Machine an 4-Quarant IGBT Converter Linke to the Rotor IEEE, Vol. 4, pp