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    Overview lvrt capability of dfig techniques Overview lvrt capability of dfig techniques Document Transcript

    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME75OVERVIEW LVRT CAPABILITY OF DFIG TECHNIQUESMustafa Jawad Kadhim, Prof.D.S.ChavanBharati Vidyapeeth Deemed University. College of EngineeringPune-Satara Road, Pune-411043ABSTRACTLow Voltage Ride Through is an important feature for wind turbine systems to meetthe conditions and requirements of the grid code. In case of wind turbine technologies usingdoubly fed induction generators the reaction to grid voltage disturbances is very sensitivewhich considers as a major drawbacks of using the Doubly Fed Induction Generators (DFIG).Protectiontechniques which include hardware or software must be implemented to protect theconverter from tripping and provide uninterruptible operation to the DFIG during severe gridvoltage faults. Methods for Ride Through operation of such system are presented.Keywords: doubly fed induction generator (DFIG); low voltage ride through (LVRT); griddefaults.I-INTRODUCTIONWind energy generation has been noted as the most rapidly growing renewable energytechnology. The increasing penetration level of wind energy can have a significant impact onthe grid, especially under abnormal grid voltage conditions. Thus, the power grid connectioncodes in most countriesrequire that wind turbines (WTs) should participate in grid voltagesupport in steady state and remain connected to the grid to maintain the reliability during andafter a short-term fault [1].The latter requirement means that WTs have low voltage ridethrough (LVRT) capability and supply reactive currents to the grid as stated in the grid codes.Among the wind turbine concepts, the doubly fed induction generator (DFIG) is a popularwind turbine system due to its high energy efficiency, reduced mechanical stress on the windturbine, separately controllable active and reactive power, and relatively low power rating ofthe connected converter [2], but due to the direct connection of the stator to the grid, theINTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING& TECHNOLOGY (IJEET)ISSN 0976 – 6545(Print)ISSN 0976 – 6553(Online)Volume 4, Issue 3, May - June (2013), pp. 75-81© IAEME: www.iaeme.com/ijeet.aspJournal Impact Factor (2013): 5.5028 (Calculated by GISI)www.jifactor.comIJEET© I A E M E
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 09766545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, MayDFIG suffers from a greatvulnerability to grid faultsforthe rotor side power electronic converter.The structure is as follows.isdescribed. FACTs devices are described in section III. Stator current feedback technique isinvestigated in IV. Aconclusion closes thetechniques.II-CROWBARFig 1:A protection system called active crowbarthe DFIG operation during the LVRT whichprotect it turningthe generator into a sqcomprise of a set of thyristors that willthereby limit the rotor voltage andvalues of the crowbar resistors result in adifferent behavior. Using this technology, the DFIGcan stayconnected to the grid and resume operation as soon as possible.disadvantage for this system is when the RSC disabled the machine draws a highshort circuitcurrent when the crowbar is activated, as describedreactive power drawn fromthe power network, which is not acceptable whenconsideringactual grid code requirements.investigated to ride-through grid faults safely andfulfill the grid codes.III-FLEXIBLE AC TRANSMISSION SYSTEMS (FACTS)Flexible AC Transmission Systems, called FACTS, got in the recent years a wellknown term for higher controllability in power systems by means of power electronicdevices. Several FACTS-devices have been introduced for various applications worldwide. Anumber of new types of devices are in the stage of being introduced in practice.In most of theapplications the controllability is used to avoid cost intensive or landscape requiringextensions of power systems, for instance like upgrades or additions of substlines. FACTS-devices provide a better adaptation to varying operational conditions andimprove the usage of existing installations.devices, shunt devices, series devices and combined shunt and sInternational Journal of Electrical Engineering and Technology (IJEET), ISSN 09766553(Online) Volume 4, Issue 3, May - June (2013), © IAEME76DFIG suffers from a greatvulnerability to grid faults [3] and requires additional protectionhe rotor side power electronic converter.The structure is as follows. In Section II, the crowbar protection techniqueFACTs devices are described in section III. Stator current feedback technique isconclusion closes the investigation of the effectiveness of the proposedFig 1: DFIG using crowbar protectionA protection system called active crowbar is one of the methods that used to enhanceeration during the LVRT whichdisconnects the rotor side converter in order toprotect it turningthe generator into a squirrel cage induction machine [4-5]. Thecrowbar maycomprise of a set of thyristors that will short-circuit the rotor windings when triggered andthereby limit the rotor voltage and provide an additional path for the rotorcurrent. Differentvalues of the crowbar resistors result in adifferent behavior. Using this technology, the DFIGcan stayconnected to the grid and resume operation as soon as possible. But the mainthis system is when the RSC disabled the machine draws a highshort circuitcurrent when the crowbar is activated, as describedin [6], resulting in a large amount ofreactive power drawn fromthe power network, which is not acceptable whenrequirements. Thus, other protection methodshave to bethrough grid faults safely andfulfill the grid codes.AC TRANSMISSION SYSTEMS (FACTS)lexible AC Transmission Systems, called FACTS, got in the recent years a wellknown term for higher controllability in power systems by means of power electronicdevices have been introduced for various applications worldwide. Aer of new types of devices are in the stage of being introduced in practice.In most of theapplications the controllability is used to avoid cost intensive or landscape requiringextensions of power systems, for instance like upgrades or additions of substations and powerdevices provide a better adaptation to varying operational conditions andimprove the usage of existing installations. There are three configurations of the FACTSdevices, shunt devices, series devices and combined shunt and series devices [7]International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –June (2013), © IAEMEand requires additional protectionIn Section II, the crowbar protection techniqueFACTs devices are described in section III. Stator current feedback technique isof the effectiveness of the proposedof the methods that used to enhanceconverter in order toThecrowbar maythe rotor windings when triggered andprovide an additional path for the rotorcurrent. Differentvalues of the crowbar resistors result in adifferent behavior. Using this technology, the DFIGBut the mainthis system is when the RSC disabled the machine draws a highshort circuitresulting in a large amount ofreactive power drawn fromthe power network, which is not acceptable whenThus, other protection methodshave to belexible AC Transmission Systems, called FACTS, got in the recent years a well-known term for higher controllability in power systems by means of power electronicdevices have been introduced for various applications worldwide. Aer of new types of devices are in the stage of being introduced in practice.In most of theapplications the controllability is used to avoid cost intensive or landscape requiringations and powerdevices provide a better adaptation to varying operational conditions andThere are three configurations of the FACTS7].
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 09766545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, MayA-STATCOMThe most used FACTSConverter called STATCOM. These shunt devices are operating as reactive powercompensators. The advantage of a STATCOM is that the reactive powerindependent from the actual voltage on the connection point.The STATCOM configuration consists of a VSC, a dc energy storage device; a couplingtransformer connected in shunt with the ac system, and associated control circuits. Fig. 2shows the basic configuration of DFig 2: STATCOM structure and voltage / current characteristicTheVoltage Source Converter (VSC) converts the dc voltage across the storage deviceinto aset of three-phase ac output voltages. These voltages arein phassystem through the reactance of the coupling transformer. Suitable adjustment of thephaseand magnitude of the STATCOM output voltages allowseffective control of active andreactive power exchangesbetween the STATCOM and the ac syB-Dynamic voltage restorer (DVR)The DVR is a powerful controller that is commonly used for voltage sags mitigationat the point of connection. The DVR employs the same blocks as the Dthis application, the coupling transformer is connected in seriesshows the basic configuration of DVR. The VSC generates a threewhich is controllable in phase and magnitude. These voltages are injected into the acdistribution system in order to maintain the load voltage at the desired voltthe DVR device is used to compensatethe faulty grid voltage, any protection method in theDFIGsystem can be left out. The advantages of such an external protectiondevice are thus thereduced complexity in the DFIG system. ThedisadvantagesDVR [9].Fig3:International Journal of Electrical Engineering and Technology (IJEET), ISSN 09766553(Online) Volume 4, Issue 3, May - June (2013), © IAEME77The most used FACTS-device is the SVC or the version with Voltage SourceConverter called STATCOM. These shunt devices are operating as reactive powercompensators. The advantage of a STATCOM is that the reactive powerindependent from the actual voltage on the connection point.The STATCOM configuration consists of a VSC, a dc energy storage device; a couplingtransformer connected in shunt with the ac system, and associated control circuits. Fig. 2the basic configuration of D-STATCOM.Fig 2: STATCOM structure and voltage / current characteristicTheVoltage Source Converter (VSC) converts the dc voltage across the storage deviceinto aphase ac output voltages. These voltages arein phase and coupled with the acsystem through the reactance of the coupling transformer. Suitable adjustment of thephaseand magnitude of the STATCOM output voltages allowseffective control of active andreactive power exchangesbetween the STATCOM and the ac system[8].Dynamic voltage restorer (DVR)The DVR is a powerful controller that is commonly used for voltage sags mitigationat the point of connection. The DVR employs the same blocks as the D-STATCOM, but inthis application, the coupling transformer is connected in series with the ac system. Fishows the basic configuration of DVR. The VSC generates a three-phase ac output voltagewhich is controllable in phase and magnitude. These voltages are injected into the acdistribution system in order to maintain the load voltage at the desired voltagedevice is used to compensatethe faulty grid voltage, any protection method in theDFIGsystem can be left out. The advantages of such an external protectiondevice are thus thereduced complexity in the DFIG system. Thedisadvantages are the cost and complexity of theFig3: Basic configuration of DVRInternational Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –June (2013), © IAEMEdevice is the SVC or the version with Voltage SourceConverter called STATCOM. These shunt devices are operating as reactive powercompensators. The advantage of a STATCOM is that the reactive power provision isThe STATCOM configuration consists of a VSC, a dc energy storage device; a couplingtransformer connected in shunt with the ac system, and associated control circuits. Fig. 2Fig 2: STATCOM structure and voltage / current characteristicTheVoltage Source Converter (VSC) converts the dc voltage across the storage deviceinto ae and coupled with the acsystem through the reactance of the coupling transformer. Suitable adjustment of thephaseand magnitude of the STATCOM output voltages allowseffective control of active andThe DVR is a powerful controller that is commonly used for voltage sags mitigationSTATCOM, but inwith the ac system. Fig. 3phase ac output voltagewhich is controllable in phase and magnitude. These voltages are injected into the acage reference. Ifdevice is used to compensatethe faulty grid voltage, any protection method in theDFIGsystem can be left out. The advantages of such an external protectiondevice are thus theare the cost and complexity of the
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 09766545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, MayC-Unified Power Flow controller (UPFC)The UPFC is a combination of a static compensator and static series compensation. Itacts as a shunt compensating and a phase shiftingFig 4: Principle configuration of an UPFCThe UPFC consists of a shunt and a series transformer, which are connected via twovoltage source converters with a common DCpower exchange between shunt and series transformer to control the phase shift of the seriesvoltage. This setup, as shown in Fig 4flow. The series converter needs to be protected with a Thyristor bridge. Due to theefforts for the Voltage Source Converters and the protection, an UPFC is getting quiteexpensive, which limits the practical applications where the voltage and power flow control isrequired simultaneously[10].D-Magnetic Energy Recovery Switch (MERS)One of the series FACTSa capacitor in aconfiguration identical to the singlearrangementin an electric circuit, however, is different, with only two of theconverter’sterminals utilized and connectevariablecapacitor and is related to FACTS controllers with series capacitors such as theGCSCand the TCSC.The investigation ofLVRTcapabilityof wind farms wconditions in the whole system and the process of achievingthis was almostHowever, found that a small 50MERS. These are most likely the esome fifth-order harmonicsinto the system, and it was found that these coincide with theresonancefrequency of the simulation model. How the application of a differentMERScapacitor or the operation in continuous mode would affect this isFig 5:International Journal of Electrical Engineering and Technology (IJEET), ISSN 09766553(Online) Volume 4, Issue 3, May - June (2013), © IAEME78ller (UPFC)The UPFC is a combination of a static compensator and static series compensation. Itacts as a shunt compensating and a phase shifting device simultaneously.Principle configuration of an UPFCThe UPFC consists of a shunt and a series transformer, which are connected via twovoltage source converters with a common DC-capacitor. The DC-circuit allows the activeween shunt and series transformer to control the phase shift of the seriessetup, as shown in Fig 4, provides the full controllability for voltage and powerflow. The series converter needs to be protected with a Thyristor bridge. Due to theefforts for the Voltage Source Converters and the protection, an UPFC is getting quiteexpensive, which limits the practical applications where the voltage and power flow control iswitch (MERS)series FACTS controllers. It consists of four power electronic switches anda capacitor in aconfiguration identical to the single-phase full bridge converter. Itsarrangementin an electric circuit, however, is different, with only two of theand connected in series. It has the characteristic of avariablecapacitor and is related to FACTS controllers with series capacitors such as theGCSCThe investigation of MERS indicated that it is able to increase theLVRTcapabilityof wind farms with DFIG. This device successfully reestablishedpreconditions in the whole system and the process of achievingthis was almostHowever, found that a small 50-Hz distortion inthe generator’s torque was caused by theMERS. These are most likely the effectof harmonic distortion created by the device. It injectsorder harmonicsinto the system, and it was found that these coincide with theresonancefrequency of the simulation model. How the application of a differenttion in continuous mode would affect this is uncertainFig 5: Typical MERS configurationInternational Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –June (2013), © IAEMEThe UPFC is a combination of a static compensator and static series compensation. ItThe UPFC consists of a shunt and a series transformer, which are connected via twocircuit allows the activeween shunt and series transformer to control the phase shift of the series, provides the full controllability for voltage and powerflow. The series converter needs to be protected with a Thyristor bridge. Due to the highefforts for the Voltage Source Converters and the protection, an UPFC is getting quiteexpensive, which limits the practical applications where the voltage and power flow control isconsists of four power electronic switches andphase full bridge converter. Itsarrangementin an electric circuit, however, is different, with only two of thed in series. It has the characteristic of avariablecapacitor and is related to FACTS controllers with series capacitors such as theGCSCMERS indicated that it is able to increase thesuccessfully reestablishedpre-faultconditions in the whole system and the process of achievingthis was almost identical.Hz distortion inthe generator’s torque was caused by theffectof harmonic distortion created by the device. It injectsorder harmonicsinto the system, and it was found that these coincide with theresonancefrequency of the simulation model. How the application of a differentuncertain [11].
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME79IV-STATOR CURRENT FEEDBACK TECHNIQUEThe proposed technique aims to reduce the rotorcurrents by changing the RSC controlinstead of installing additional hardware protection like a crowbar in the wind turbine system.The solutionhas been presented in [12]. When a fault affects the generator the measured andtransformed statorcurrents are fed back as reference for the rotor current controller (statorcurrents in stator flux orientation).The objective is to reduce stator current oscillations andthus reduce the rotor currents aswell.If the DFIG system equations are combined as in [13], aLaplace transformation is performed and somesimplifications are assumed, the followingequation for the stator currents can be obtained:)2.........(21)1.........(212222rqshsqsssssssqrdshsqssssssdiLLvsLRsLRsLiiLLvsLRsLi−+++=−++=ωωωIf the stator currents are fed back as rotor current reference values, i.e. sdrd ii =+and sqrq ii =+thefollowing equation for the stator currents can be obtained and the stator currents are reduced.)4..(..........21)3.(..........212222sqssssshssqsqsssshssdvsLRsLRsLLivsLRsLLiωωω++++=+++=V-CONCLUSIONLow Voltage Ride Through is an important feature for wind turbine systems to fulfillgrid code requirements. In case of wind turbine technologies using doubly fed inductiongenerators the reaction to grid voltage disturbances is sensitive. Hardware or softwareprotection must be implemented to protect the converter from tripping during severe gridvoltage faults. In this paper the proposed techniques have been investigated to show theireffectiveness to enhance the Doubly Fed Induction Generator (DFIG) capability of LowVoltage Ride through (LVRT).
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME80REFERENCES[1]Tsili, M.; Papathanassiou, S. A review of grid code technical requirements for wind farms.IET Renew. Power Gen. 2009, 3, 308–332.[2] Thomas, A. Wind Power in Power Systems; Wiley: New York, NY, USA, 2005.[3]Mohseni, M.; Islam, S.; Masoum, M. Impacts of symmetrical and asymmetrical voltagesags on DFIG-based wind turbines considering phase angle jump, voltage recovery, and sagparameters. IEEE Trans. Power Electron. 2011, 26, 1587–1598.[4] L. Shi, N. Chen and Q. Lu, "Dynamic Characteristic Analysis of Doublyfed InductionGenerator Low Voltage Ride-through", ScienceDirect, Energy Procedia 16 (2012) 1526 –1534, doi:10.1016/j.egypro.2012.01.239.[5] Christian Wessels, Fabian Gebhardt and Friedrich W. Fuchs, "Dynamic Voltage Restorerto allow LVRT for a DFIG Wind Turbine", IEEE International Symposium on IndustrialElectronics (ISIE), 2010, doi: 10.1109/ISIE.2010.5637336.[6] J. Morren and S. de Haan, “Short-circuit current of wind turbines with doubly fedinduction generator,” IEEE Trans. Energy Convers., vol. 22, no. 1, pp. 174–180, Mar. 2007.[7] Y.H. Song, A.T. Johns, Flexible AC Transmission Systems (FACTS), IEE, London 1999.[8] R. Mineski, R. Pawelek, I. Wasiak, “Shunt compensation for power quality improvementusing a STATCOM controller: modeling and simulation”, IEE Proc. on Generation,Transmission and Distribution, Vol. 151, No. 2, March 2004.[9] M. H. J. Bollen, Understanding Power Quality Problems Voltage Sags and Interruptions.New York: Wiley, 2000.[10] Alharbi, Y.M. ; Electr. &Comput. Eng. Dept., Curtin Univ., Perth, WA, Australia; Yunus, A.M.S. ; Abu Siada, A. "Application of UPFC to improve the LVRT capability ofwind turbine generator" IEEE ,Conference Publications, date 26-29 Sept. 2012,inUniversities Power Engineering Conference (AUPEC), 2012 22nd Australasian.[11] J. A. Wiik, F. D. Wijaya, R. Shimada, “An Innovative Series Connected Power FlowController, Magnetic Energy Recovery Switch (MERS),” in Proc. Power Engineering SocietyGeneral Meeting, pp. 1-7, 2007.[12] K. Lima, A. Luna, P. Rodriguez, E. Watanabe, R. Teodorescu, and F. Blaabjerg,“Doubly-fed inductiongenerator control under voltage sags,” Energy 2030 Conference, 2008.ENERGY 2008. IEEE, pp. 1–6, Nov. 2008.[13] C. Wessels, F.W. Fuchs "LVRT of DFIG Wind Turbines - Crowbar vs. Stator CurrentFeedback Solution –"Energy Conversion Congress and Exposition, (ECCE), 2010, IEEE,conference date 12-16 sep 2010, in Atlanta, GA.[14] Ameer H. Abd and D.S.Chavan, “Impact of Wind Farm of Double-Fed InductionGenerator (DFIG) on Voltage Quality”, International Journal of Electrical Engineering &Technology (IJEET), Volume 3, Issue 1, 2012, pp. 235 - 246, ISSN Print : 0976-6545,ISSN Online: 0976-6553.[15] Nadiya G. Mohammed, “Application of Crowbar Protection on DFIG-Based WindTurbine Connected to Grid”, International Journal of Electrical Engineering & Technology(IJEET), Volume 4, Issue 2, 2013, pp. 81 - 92, ISSN Print : 0976-6545, ISSN Online:0976-6553.[16] Nadiya G. Mohammed, Haider Muhamad Husen and Prof. D.S. Chavan, “Fault Ride-Through Control for A Doubly Fed Induction Generator Wind Turbine Under UnbalancedVoltage Sags”, International Journal of Electrical Engineering & Technology (IJEET),Volume 3, Issue 1, 2012, pp. 261 - 281, ISSN Print : 0976-6545, ISSN Online: 0976-6553.
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 3, May - June (2013), © IAEME81AUTHORSMustafa Jawadkadhim Al-Tameemi, was born in Baghdad, Iraq onJan 16,1986. He received B.Sc Degree in department of electrical engineeringat University of Technology, Baghdad, Iraq in 2007. He is currently M.Techelectrical (Power Systems) candidate in BharatiVidyapeeth DeemedUniversity, College of Engineering, Pune, India.Prof . D.S. Chavan: Ph D (Registered), ME (Electrical), BE (Electrical),DEE Associate Professor, Co-ordinator (R&D cell), Co-ordinator(PH.D.Programme management) BharatiVidyapeeth Deemed UniversityCollege Of Engineering Pune 411043. He is pursuing Ph D. He received ME(Electrical)(Power systems) Achieved rank certificate in Pune University for