A new control methods for offshore grid connected wind energy conversion system using

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A new control methods for offshore grid connected wind energy conversion system using

  1. 1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME305A NEW CONTROL METHODS FOR OFFSHORE GRID CONNECTEDWIND ENERGY CONVERSION SYSTEM USINGDOUBLY FED-INDUCTION GENERATOR AND Z-SOURCEINVERTER1B.Sivaprasad, 2O.Felix,3K.Suresh, 4G.Pradeep Kumar reddy, 5E.Mahesh1,2Assistant Professor,EEE DEPT,NBKRIST,Vidyanagar,India3,4,5M.TechScholor, Department Of Electrical Engineering, N.B.K.R.I.S.T, Vidyanagar,INDIA.ABSTRACTThis paper presents a systematic approach based on. New controlling methods. Andvarious technologies are developed for wind energy conversion system. Induction generatorsare used by these technologies due to special characteristics of induction generators. Such aslow weight and volume, high performance, high speed-torque control. In this paper, a newvariable-speed WECS with an induction generator and Z-source inverter is proposed.Characteristics of Z-source inverter are used for maximum power tracking control anddelivering power to the grid, simultaneously. Two control methods are proposed fordelivering power to the grid. Capacitor voltage control and dc-link voltage control operationof system with these methods is compared from. View point of power quality and totalswitching device power (TSDP).In addition, TSDP, current ripple of inductor performanceand total harmonic distortion of grid current of proposed system is compared with traditionalwind energy system with a boost converter.IndexTerms-Doubly-Fed Induction generator (DFIG), capacitor voltage control, dc-linkvoltage control, total switching device power (TSDP), wind energy conversion system(WECS), Z-source inverter.INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING& TECHNOLOGY (IJEET)ISSN 0976 – 6545(Print)ISSN 0976 – 6553(Online)Volume 4, Issue 2, March – April (2013), pp. 305-323© IAEME: www.iaeme.com/ijeet.aspJournal Impact Factor (2013): 5.5028 (Calculated by GISI)www.jifactor.comIJEET© I A E M E
  2. 2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME306I. INTRODUCTIONWind energy is a sustainable resource due to the absence of total ecosystem pollutionand environment. Wind turbines usage as source of energy has increased significantly in theworld. With growing application of wind energy conversion system (WECS), varioustechnologies are developed for them the most common type of megawatt class wind energyconversion system employs induction generators because they are relatively inexpensive,rigid and require low maintenance. [1]-[5] However, the impact of ever-changing wind speedon power quality coupled with the need for an excitation current make the voltage regulationdifficult, especially when IG is connected to a weak ac system. Extracting maximum powerfrom wind and feeding the grid with high quality electricity are two main objectives forWECS, to realize these objectives; the ac-dc-ac converter is one of the best topology forWECS.Fig-1 shows a conventional configuration of ac-dc-ac topology for IG.Fig.1. Conventional PMSG-based WECS with dc boost chopper.This configuration includes diode rectifier, boost dc-dc converter and three phaseinverter, in this topology, boost converter is controlled for maximum power point tracking(MPPT) and inverter is controlled to deliver high quality power to the grid. The Z-sourceinverters have been reported recently as a competitive, alternative to existing invertertopologies with many inherent advantages such as voltage boost this inverter facilities voltageboost capability with the turning ON OF both switches in the same inverter phase lag (shootthrough state). In this paper, a new IG-based WECS with Z-source inverter is proposed theproposed topology is shown in Fig-2 with this topology boost converters omitted without anychange in the objectives of WECS.Fig. 2. Proposed PMSG-based WECS with Z-source inverter.
  3. 3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME307Moreover, reliability of the system is greatly improved, because the short circuit across anyphase lag of inverter is allowed. Also, in this configuration, inverter output power distortion isreduced, since there is no need to phase lag dead time.[6] Section-2 of this paper introducesZ-source inverter and describes operation of rectifier feeding the Z-source inverter thenpower delivery and MPPT control of system are explained. Finally, simulation results arepresented to verify the performance of the proposed system.II. Z-SOURCE INVERTERThe Z-source inverter is shown in Fig-3.Fig. 3. Voltage-type Z-source inverterThis inverter has an impedance network on its dc side, which connects the source tothe inverter. The impedance network is composed of two inductors and capacitors. Theconventional voltage source inverter has six active vectors and zero vectors. However, the Z-source inverter has one extra zero vector(state) for boosting voltage that is called shootthrough vector.[14] In this state, load terminals are shorted through both the upper and lowerdevices of phase lag, any two phase lags, or all three phase lags.The voltage of DC-link can be expressed asWhere Vdc is the source voltage and B is the boost factor that is determined byWhere to be the shoot- through time interval over a switching cycle. The output peak phasevoltage Vac isWhere M is the Modulation index. The capacitor voltage can expressed as.
  4. 4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME308WhereRelation between Vi and Vc can be written as.And current ripple of inductors can be calculated by.Fig.4 explains the simple PWM control method for Z-source inverter. This method employstwo extra straight lines as shoot through signals, Vsc and –Vsc. [8] When the career signal isgreater than Vsc or it is smaller than –Vsc, a shoot-through vector is created by inverter .Thevalue of Vsc is calculated by.Fig. 4. PWM control method for Z-source inverter.In the proposed WECS, a diode rectifier bridge with input capacitors (Ca,Cb,Cc) serves asthe DC source feeding the Z-source inverter. The configuration is shown in Fig-5 the inputcapacitors suppress voltage surge that may occur due to the line inductance during diodecommutation and shoot through mode of the inverter.Fig. 5. Z-source inverter fed with a diode rectifier bridge.
  5. 5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME309At any instant of time, only two phases that have the largest potential difference mayconduct, carrying current from the IG side to the impedance. Fig-6 shows six possible statesduring each cycle.Fig. 6. Six possible conduction intervals for the rectifier.In any state ,one of upper diodes, one of lower diodes and the corresponding capacitor areactive.[7] For example, when the potential difference between phases “a” and “b” is thelargest, diodes Dpa and Dnb conduct in series with capacitor Ca as shown in Fig-7.Fig. 7. Equivalent circuit when the potential difference between phases “a”And “b” is the largestIn each conduction interval, inverter operates in two modes. [13] In mode1, the inverter isoperating in the shoot-through state. In this mode, the diodes (Dpa and Dnb) are off, and the dclink is separated from the ac line. Fig-8 shows the equivalent circuit in this mode.Fig. 8. Equivalent circuit of the Z-source inverter in mode 1.In mode 2, the inverter is applying one of six active vectors or two zero vectors, thus acting asa current source viewed from the Z-source with diodes (Dpa and Dnb) being on Figh-9 showsthe equivalent circuit in this mode. [9] The load current I1 is zero during zero vectors.
  6. 6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME310Fig. 9. Equivalent circuit of the Z-source inverter in mode 2III.CONTROL SYSTEMThe structure of the control system is shown in Fig-10 the control system is proposedof two parts: 1. control of power delivered to the grid and 2. MPPT.Fig. 10. Block diagram of proposed WECS control system.A. Control of power delivered to the grid:The power equations in the synchronous reference frame are given by.Where P and Q are the active and reactive power, respectively, V is grid voltage, and I isthe current to the grid.[17] The subscripts D and ‘q’ stands for direct and quadraturecomponents, respectively. If the reference frame is oriented along the grid voltage, Vq will beequal to zero. Then, active and reactive power may be expressed as
  7. 7. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME311According to earlier active and reactive power control can be achieved by controlling directand quadrature current components, respectively. [10] Two control paths are used to controlthese currents. In the first path, with given reactive power, the q-axis current reference is setto obtain unit power factor, the q-axis current, reference should be set to 0.In the second pathan outer capacitor voltage control loop is used to set the d-axis current reference for the activepower control. This assures that all the power coming from the rectifier is transferred to thegrid. For this control, two methods are proposed; 1. Capacitor voltage (VC) control and 2. Dc-link voltage (Vi) control.In the first control method (control mode 1 in Fig-0), capacitor voltage is kept constant atreference value .In the control loop, when shoot through time changes, Vdc and Vi willchange.[16] However, in other method (control mode2 in Fi -10) , a reference value is set fordc-link voltage(Vi). In this method, with changing shoot through time, Vdc and VC willchange. The input voltage of inverter is zero in shoot through state, which makes Vi a difficultvariable to control consequently is used to control Vi in directly by controlling VC . In sectioniv, operation of system using these methods will be comparedB.Maximum Power Point Tracking:The mechanical power delivered by a wind turbine is expressed asWhere ρ is the air density, A is the area swept out by the turbine blades, Vw is the windvelocity, and Cp is the power coefficient defined as the ratio of turbine power to wind powerand depends on the aerodynamic characteristic of blades. Fig (11) represents the relationbetween generator speed and output power according to the wind speed change.Fig. 11. Mechanical power versus rotor speed with the wind speed as aParameter.It is observed that the maximum power output occurs at different generator speed fordifferent wind velocities. The steady-state induced voltage and torque equations of IG aregiven by.
  8. 8. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME312Where W is rotor speed and Ia is stator current. Also we haveWhere Vis terminal voltage of IG and Ls is its inductance the rectified dc-link voltage may beobtained using.From 15to 17, the rectified dc voltage may be written asThe torque is determined by the generator speed and the wind speed, therefore accordingto 18, it is possible to obtain a prediction for the dc voltage as a function of the generatorspeed and the wind speed. As result, the generator speed can regulate by setting the dcvoltage. Fig -12 shows the rectified dc voltage versus rotor speed for maximum wind poweroperating point using rotor speed feed back and Fig-12 , the optimum rectified dc voltage isspecified.Fig. 12. DC voltage versus optimum rotor speed characteristic.Using new optimum dc voltage, IG rotor speed will change and a new dc voltage. Commandis specified from Fig-12 with this control strategy, IG rotor speed dc voltage is continuouslychanged until an equilibrium point is reached in Fig-12[15] .one can see from Fig -12 that thevoltage –speed relationship is not a straight line. In order to implement a simple a controlstrategy as possible, it is desirable to implement a straight line. Voltage-speed relationship. Inthis paper quadratic approximation of the voltage speed relationship is used. Afterdetermining optimum dc voltage from voltage seed curve, shoot through signal Vsc PWMcontrol is calculated bx.
  9. 9. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME313TABLE I. PARAMETERS OF DFIGPARAMETER VALUERS 0.8785Lq 5.8mHLd 5.6mHP 8J 9.329Kg.cm2IV. SIMULATIONTo verify the performance of the proposed MECS, several simulation tests areperformed. The simulated system parameters are listed in Tables I and II. Fig- 12 s plottedusing mathematical model of the turbine and IG. The optimum curve can also be obtained bysome tests in various wind speed. Solid curve in Fig-13 is dc voltage versus optimum rotorspeed.Fig. 13. DC voltage and optimum rotor speed relation: simulated and approximated andcalculated (actual).This curve is plotted with simulation of WECS for various wind speed and rotor speed.Dotted curve is a quadratic approximation of the bold curve . In next dotted curve is used formaximum power control. The maximum and minimum rotor speeds are considered as 1.3 and0.6pu respectively.Simulation of Proposed System:In order to evaluate the dynamic performance of the proposed WECS, it is simulated for 4s.The wind speed is shown in Fig-14.Fig. 14. Wind speed variation.
  10. 10. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME314Two simulations were performed using two different methods for active power control asmentioned in section II.TABLE II. SIMULATION PARAMETERSPARAMETER VALUEVG 84VLi 10MhL1,L2 4MhC1,C2 10KHz1) Capacitor voltage control method: In this section, the proposed system is simulatedusing capacitor voltage control of Z-source inverter .Reference voltage for capacitor was setto 140 V Fig-15shows IG rotor speed.Fig. 15. PMSG rotor speed (capacitor voltage control)To obtain maximum power control, the rotor speed has changed with changing wind speedFig-16 shows maximum mechanical power of turbine and extracted mechanical power fromturbine .Fig. 16. Maximum mechanical power of turbine and the extracted mechanical power fromturbine (capacitor voltage control).
  11. 11. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME315It is that extracted mechanical power is tracking the maximum mechanical power after ashort time Fig-17 shows capacitor voltage.Fig. 17. Capacitor voltage (capacitor voltage control).Which is almost constant reactive power that is kept at zero (unity power factor) is alsoshown in Fig-18 Fig 19 shows active power delivered to the grid and the extractedmechanical power .Fig. 18. Active power delivered to the grid and extracted mechanical power(Capacitor voltage control).The electrical power delivered to the grid is different from the extracted mechanical powerdue to electrical and mechanical losses. Inductor current is shown in Fig-20.Fig. 19. Inductor current of Z-source inverter (capacitor voltage control).
  12. 12. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME316It is seen that the inductor current is variable, however current is almost constant.Fig. 20. Input voltage of Inverter (Vi ) (capacitor voltage control).In Fig-21 the input voltage of inverter (Vi) is shown .For MPPT control ,Vi has changed withvariations of wind speed , while capacitor voltage is constant (Fig-17) that was expected fromcapacitor voltage control method.2) DC link voltage control method: the previous simulation was repeated using dc linkvoltage control .Reference voltage for dc link of Z-source inverter was set to 165 V .Fig-22-24shows rotor speed maximum mechanical power of turbine / the extracted mechanicalpower, and active power delivered to the grid.Fig. 21. PMSG rotor speed (dc-link voltage control).Fig. 22. The maximum mechanical power of turbine and the extracted mechanical powerfrom turbine (dc-link voltage control).
  13. 13. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME317Fig. 23. Active power delivered to the grid and extracted mechanical power(Dc-link voltage control)..In dc-link voltage control method, for MPPT control, capacitor voltage must change whilev1 is constant as shown in fig 25 and 26.Fig. 24. Capacitor voltage (dc-link voltage control).Fig. 25. Input voltage of Inverter (Vi ) (dc-link voltage control).
  14. 14. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME318The capacitor has slow dynamics on the other hand, there is a right half plane (RHP) zero inthe transmitter function of VC, which causes undershoot in capacitor voltage. However, it isnot a concern for MPPT control because dynamics of wind and turbine are slow too. We cansee small undershoots in root speed(fig 22)that are not shown in (fig 15).These undershootshave no considerable effect on MPPT as the extracted mechanical power in figs16 and23.But variation of capacitor voltage has more effect on power deliver as shown in fig24,electrical power has more fluctuations than shown in fig 19.A. Operation Of Constant Wind Speed: In order to evaluate the performance of theproposed system, another simulation is performed using constant wind speed (10m/s) andwith capacitor voltage control. Fig 27 illustrates dc-link voltage across rectifier that ischanging from 95to 280v.with respect to fig8.Fig. 26. DC-link voltage across the rectifier.Fig. 27. DC-link voltage across the Z-source inverterwhen a shoot through vector is applied to Z-source inverter ,dc link voltage of rectifierwill be twice as much as the capacitor voltage(280v)with reference to fig 13.When win dspeed is 10m/s,dc-link voltage across rectifier must be 95v for MPPT.DC-link voltage acrossZ-source inverter is shown in fig 28,which is zero in shoot –through time intervals and 185vin other times according to figs 29 and 30 illustrate the inductor current with respect tocurrent ripple must be 0.85A.This is shown in fig 30.
  15. 15. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME319Fig. 28. Inductor current of Z-source inverter (zoomed).However there is a low-frequency larger ripple, Because Z-Source inverter is fed by anuncontrolled rectifier. Fig 31 and 32 shows grid-current and its spectra. THD of injectedcurrent is 2.95%.Fig. 29. Grid current in proposed WECS.Fig. 30. Spectra of grid current in proposed WECS.B. Comparison with conventional system:In this section, the proposed WECS is compared with conventional WECS usingboost converter replacing the Z-source network, as shown in fig (1). PWM switching methodis implemented to keep DC bus voltage constant that switching pulse is generated by a newcontrol box using Vc and Vdc. Inductance and capacitance of boost converter is selectedtwice as much as of the proposed system that is 4mH and 4400µF. TO correct comparison,traditional WECS was simulated in condition similar to previous simulation.
  16. 16. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME320Fig.31. Inductor current of boost converter.3) Inductor Current Ripple: As shown in fig-33, the inductor current ripple is 0.38A asexpected from theory the current ripple for the proposed WECS, as shown in fig 30, is twiceas much that is 0.85A. As shown in fig 34.There is a low-frequency ripple caused byuncontrolled rectifier. The same ripple is shown in fig 29. For the proposed WECS.4) Grid current THD: In a conventional inverter, added time is included in the switching ofsemiconductors to accidental short circuit in an inverter lag. Two simulations are performedwith 0 and 5µs dead time using conventional WECS with boost converter> fig 35 and 36insulate the grid current and its spectra for zero dead time simulation.Fig.32. Spectra of grid current in traditional WECS without dead time.THD is 3.1% that nearly equals THD of current in proposed WECS. Figs 37 and 38 show thegrid current and its spectra for 5µs dead time simulation. THD has increased to 4.96%.5) Efficiency: In order to compare efficiency, both proposed and conventional WECS wassimulated with various wind speeds. The active electrical power delivered to grid versus windspeeds is shown in fig 39.
  17. 17. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME321Fig.33. Active power delivered to the grid in conventional and proposedWECSIn each simulation efficiency is calculated by dividing the active electrical power by themaximum mechanical power (according to fig 11) fig 40 illustrates the efficiency of bothsystems in various wind speeds.Fig..34 Efficiency of conven34tional and proposed WECSs.According to fig 40, efficiency of conventional WECS is smaller than that of the proposedWECS, approximately 4% the reason is the extra and diode in conventional WECS withboost converter.6) Total switching device power: The total switching device power (TSDP) is calculatedasWhere N is the number of semiconductor devices, Vsj and Isj are voltage stress and currentstress of device, respectively, Cj is cost factor, and Cj is defined as 1 for semiconductorswitch and 0.5 for diode.Table 3 shows TSDP of WECS system with boost converter, proposed WECS withvoltage control of capacitor , and proposed WECS with voltage control of DC link. It is seenthat TSDP of proposed WECS with capacitor voltage control is bigger than conventionalWECS. However, with dc link, voltage capacitor, TSDP is increased only 6%.
  18. 18. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME322V CONCLUSIONIn this paper, an IG –based WECS with Z-source inverter is proposed, Z-sourceinverter is used for maximum power tracking control and delivering power to the grid.Simultaneously compared to conventional WECS with boost converter, the number ofswitching semiconductors is reduced by one and reliability of system is improved, becausethere is no requirement for dead time in a Z-source inverter. For active power control, twocontrol methods: capacitor voltage control and dc-link voltage control is proposed andcompared. It is shown that with dc-link voltage control method, TSDP is increased only 6%compared to conventional system, but there is more power fluctuations compared to capacitorvoltage control. With capacitor voltage control TSDP is increased 19% compared toconventional system. It was also shown that due to eliminating of dead time, the THD ofproposed system is reduced by 60% compared to conventional system by 3ms dead time.Finally, with same value to passive components, inductor current ripple is the same for bothsystems.VI REFRENCES[1] P. C. Loh, D. M. Vilathgamuwa, C. J. Gajanayake, Y. R. Lim, and C. W. Teo,“Transient modeling and analysis of pulse-width modulated Z-source inverter,” IEEE Trans.Power Electron., vol. 22, no. 2, pp. 498– 507, Mar. 2007.[2] F. Z. Peng, A. Joseph, J.Wang, andM. Shen, “Z-source inverter for motor drives,” IEEETrans. Power Electron., vol. 20, no. 4, pp. 857–863, Jul.2005.[3] E. Spooner and A. C. Williamson, “Direct coupled permanent magnet generators forwind turbine applications,” Inst. Elect. Eng. Proc., Elect. Power Appl.,vol. 143, no. 1, pp. 1–8, 1996.[4] A. M. Knight and G. E. Peters, “Simple wind energy controller for an expandedoperating range,” IEEE Trans. Energy Convers., vol. 20, no. 2, pp. 459–466, Jun. 2005.[5] T. Tafticht, K. Agbossou, A. Cheriti, and M. L. Doumbia, “Output power maximizationof a permanent magnet synchronous generator based standalone wind turbine,” in Proc.IEEE ISIE 2006, Montreal, QC, Canada, pp. 2412–2416.[6] M. Shen, A. Joseph, J. Wang, F. Z. Peng, and D. J. Adams, “Comparison of traditionalinverters and Z-source inverter,” in Proc. Power Electron.Spec. Conf., 2005, pp. 1692–1698.[7] N. Yamamura, M. Ishida, and T. Hori, “A simple wind power generating system withpermanent magnet type synchronous generator,” in Proc. IEEE Int. Conf. Power Electron.Drive Syst., 1999, vol. 2, pp. 849–854.[8] S. H. Song, S. Kang, and N. K. Hahm, “Implementation and control of grid connectedAC–DC–AC power converter for variable speed windenergy conversion system,” Appl.Power Electron. Conf. Expo., vol. 1, pp. 154–158, 2003.[9] M. Chinchilla, S. Arnaltes, and J. C. Burgos, “Control of permanentmagnet generatorsapplied to variable-speed wind-energy systems connected to the grid,” IEEE Trans. EnergyConvers., vol. 21, no. 1, pp. 130–135, Mar. 2006.[10] F. Z. Peng, “Z-source inverter,” IEEE Trans. Ind. Appl., vol. 39, no. 2, pp. 504–510,Mar./Apr. 2003.[11].A.Mudroch,R.Barton,J.R.Winlelman,And S.H.Javid,”Control Design And PerformanceAnalysis Of A 6mw Wind Turbine Generator”Ieee Trans.Power System Vol.PAS-102,Pp,1340-1347,Dec,1983.
  19. 19. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME323[12] Ackermann, T.(ed) .2005 Wind Power In Power Systems.Wiley,England.[13] Bongers, p.vanbaars ,G.(1992) Wind Turbine Control Design And Implementation[14] “Wind Energy Explained-Theory, Design & Application” – By J.F. Manwell, J.G.McGown, A.L. Rogers.[15] Balas, M. Fingersh, L. Johnson, K. pao, L.(2006) Control Of Variable-Speed WindTurbines: Standard And Adaptive Techniques For Maximizing Energy Capture.[16] De Montfort University (2007) Wind Energy Training Course. [Online]from:www.iesd.dmu.ac.uk/wind_energy/m32extex.html[Accessed in February 2007]. Dorf, R. (2000) The Electrical Engineering Handbook.CRC Press LLC, Florida[17] Bemporad, A. Morari, M. Dua, V. Pistikopoulos, E.(2002)The explicit linear quadraticregulator for constrained systems, Automatica, [Online] 38,3-20 Available from:www3.imperial.ac.uk/library/digitallibrary/electronicjournals[Accessed May 2007].[18] P.H. Zope, Prashant Sonare, Avnish Bora and Rashmi Kalla, “Simulation andImplementation of Control Strategy for Z-Source Inverter in the Speed Control of InductionMotor”, International Journal of Electrical Engineering & Technology (IJEET), Volume 3,Issue 1, 2012, pp. 21 - 30, ISSN Print : 0976-6545, ISSN Online: 0976-6553.[19] P.H. Zope and Ajay Somkuwar, “Design and Simulation of Single Phase Z-SourceInverter for Utility Interface”, International Journal of Electrical Engineering & Technology(IJEET), Volume 1, Issue 1, 2010, pp. 127 - 143, ISSN Print : 0976-6545, ISSN Online:0976-6553.[20] Mr. Laith O. Maheemed, Prof. D.S. Bankar and Dr. D.B. Talange, “Power QualityImprovement of Wind Energy Conversion System using Unified Power QualityConditioner”, International Journal of Electrical Engineering & Technology (IJEET),Volume 3, Issue 1, 2012, pp. 288 - 302, ISSN Print : 0976-6545, ISSN Online: 0976-6553.[21] Nadiya G. Mohammed , HaiderMuhamadHusen 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.[22] Haider M. Husen, Laith O. Maheemed and Prof. D.S. Chavan, “Enhancement of PowerQuality in Grid-Connected Doubly Fed Wind Turbines Induction Generator”, InternationalJournal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 1, 2012,pp. 182 - 196, ISSN Print : 0976-6545, ISSN Online: 0976-6553.

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