Full-scale converter for synchronous wind turbine generators

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  • DFIG have another connection to transfer 70% of the energy out to the grid, PE only transfer 30%; FSC transfer 100% power from Generator to grid through power electronics. All We’ll talk about SG -> Circuit Topology for Converter -> how to control
  • Mitsubishi Heavy IndustriesWind Power Technologies
  • Full-scale converter for synchronous wind turbine generators

    1. 1. CLASS REE527: WIND POWER GENERATOR GROUP 7 Full Scale Converter for Synchronous Full Scale Converter Wind Turbine Generators for Synchronous WTG Presented by: L. Yang & L. Pham Nov. 2013
    2. 2. Agenda 1. 2. 3. 4. 5. 6. Introduction – The Evolution of modern WT Characteristic Design Control Application Conclusion – The Future
    3. 3. 1. Introduction – The evolution of WT
    4. 4. Wind turbine system evolution Wind energy conversion system convert kinetic energy of the wind into electricity or other forms of useful energy Increased wind turbine size over the years, larger capacity turbines reaching 5-7 MW level Increased the use of power electronics, allows more control of the power generation Rapid growth for variable-speed wind turbine system with fullcapacity power converter F. Blaabjerg and Z. Chen, “Power Electronics for Modern Wind Turbines,” Morgan & Claypool Publishers, 2006, pp. 30-55
    5. 5. wind energy conversion system  rotation speed: 1. fixed-speed turbines 2. variable-speed turbines - classification based on the drive train components: 1) Indirect drive (with gearbox) 2) Direct drive (without gearbox)  power electronics: 1. WGS with no power converter 2. WGS with a partial-capacity power converter 3. WGS with a full-capacity power converter Wu B., Lang Y., Zargari N., Kouro S, “Power conversion and control of wind energy systems,” Wiley-I EEE press, 2011, pp. 16-35
    6. 6. 2. Characteristic
    7. 7. Variable – speed wind turbines Wu B., Lang Y., Zargari N., Kouro S, “Power conversion and control of wind energy systems,” Wiley-I EEE press, 2011, pp.16-35  Achieve maximum efficiency over a wide range of wind speeds compared with fixed speed wind turbines which only reach peak efficiency at a particular wind speed  variable speed systems could lead to maximize the capture of energy during partial load operation  Can use either induction generator or a synchronous generator  Can operate gearless, lowers the cost
    8. 8. Full-scale converter for WTS R. Teodorescu, M. Liserre, P. Rodriguez, “Grid Converter Structures for Wind Turbine Systems” in Grid Converters for Photovoltaic and Wind Power Systems, 1st ed. Chichester, UK. John Wiley & Sons, 2011, pp. 123-143. In the early 2000s, Enercon and Siemens introduced the concept of full-scale converter (FSC) for Wind Turbine Systems All power extracted from the wind is managed and transferred to grid The machine-side of the FSC can provides the generators torque and speed control The grid-side can perform reactive power compensation and supply constant DC voltage to the grid
    9. 9. Short-circuit behavior comparison shows: DFIG resulting high current surge because it is directly connected to the grid. FSC does not have a current surge because it is decoupled from grid.
    10. 10. Variable-Speed WTS using wound-rotor synchronous generators (WRSG) • In the WRSG, the rotor flux is generated by the rotor field winding  Advantage: • The WRSG with more numbers of poles and operates at low rotational speeds can be used for gearless direct-driven wind turbine. Disadvantages: 1) Large numbers of field winding – field loss, heavy weight, more expensive, large diameter 2) DC excitation required - standby power requirement
    11. 11. Variable-Speed WTS using permanent-magnet synchronous generators (PMSG) • The PMSG uses permanent magnets on the rotor to produce the magnetic field.  Advantages: 1) high power density as well as high efficiency can be achieved due to no field winding 2) Multipole PMSG with a full-capacity converter can also achieve gearless direct-driven wind turbine 3) No additional power supply for the magnet field excitation 4) Higher reliability due to the absence of mechanical components such as slip rings.  Disadvantages: 1) High cost of rare-earth magnets 2) Demagnetization of permanent magnets at high temperature
    12. 12. Overall Characteristics Advantages: 1. High energy conversion efficiency 2. reduced mechanical stress on the wind turbine 3. can operate gearless which lowers the cost 4. enables full control of the real and reactive power generated Disadvantages: 1. More components - increased equipment capital cost 2. Increased complexity of the system
    13. 13. 3. Design
    14. 14. Design of a Gearless Wind Turbines (Enercon)
    15. 15. Variable Speed WECS - Configuration 70% Any types of Generator
    16. 16. DC/DC BOOST CONVERTER INTERFACED SG WIND ENERGY SYSTEM • The simplest circuit topology. • Has a diode bride, DC/DC boost & 2 level VSI • Advantages are low cost and simple control. • Drawbacks: Stator current is distorted not sinusoidal > Harmonic losses, torque ripples, etc. • For Low power
    17. 17. DC/DC BOOST CONVERTER INTERFACED SG WIND ENERGY SYSTEM • For higher power: ▫ 2 or 3 channels interleaved (phase shift) boost converter ▫ 12-pulses rectifier  Increase current  reduce harmonic • Preferable for low- and medium-power WTS from a few kilowatts to ~1MW
    18. 18. Harmonic distortion - Comparison Next topology Back-to-Back VSI
    19. 19. Two-Level Back-To-Back Voltage-Source Converters • Most popular • 2 VSI on each side • Very flexible, lower harmonics • High switching loss (hard switching) • Big DC link capacitor
    20. 20. 3-Level Back-To-Back Neutral Point Clamped • The desires for MV: ▫ In a LV 690V/2MW: ~ 1700A each phase transferred from a nacelle to ground!
    21. 21. Multi-Level Converter Create a sinusoidal high voltage output from several levels of voltage
    22. 22. 3-levels & multi-levels Advantages Drawbacks • Lower harmonic distortion • Lower voltage change rate (dv/dt) • Higher working voltage. • Lower switching loss. • Lower EMI, etc. • Require more switching components (higher cost) • Complexity in design, control • High conducting loss Preferable for WTS with rated power over 2MW
    23. 23. Integrated gate-commutated thyristor (IGCT)
    24. 24. Integrated gate-commutated thyristor (IGCT)
    25. 25. 4. Control
    26. 26. Phasor Representation of 3-phase Variables Phasor = Phase + Vector Any 3-phase variable can be represented as a phasor rotating with angular velocity w. http://www.ece.umn.edu/users/riaz/a nim/spacevectors.html http://www.ece.umn.edu/users/ri az/anim/spacevector_viewb.html
    27. 27. Synchronous dq rotating frame Synchronous dq rotating frame is a rectangular frame rotating at angular velocity w. Phasor of a 3-phase variable can also be expressed in the synchronous dq rotating frame. The frame rotating at the same angular velocity with the vector => the component in d- and q- axis are constants (if the vector magnitude = const) http://www.ece.umn.edu/users/riaz/anim/d q_transformations.html
    28. 28. Full Scale Converter
    29. 29. Control of grid side converter • Based on instantaneous power theory. For any dq frame we have: • For a particular dq reference frame that has the d axis aligned with grid voltage phasor e
    30. 30. Control of Generator Side • Wind speed and decide the optimal torque Tmppt that generator should have to maximize power captured from the wind (MPPT) • Generator side converter control the generator so that the output torque equal Tmppt • Electromagnetic torque output Te of the generator expressed in dq synchronous reference frame: Ld, Lq, id , iq : d- and q- axis synchronous inductances and current of stator ΨPM : magnet flux of rotor
    31. 31. Non-salient Generator: Zero d-axis Current Ld = Lq
    32. 32. Salient-pole Generator: MTPA : Ld < Lq
    33. 33. 4. Application
    34. 34. Application: onshore wind power • Before: variable speeds were used to smooth out the torque fluctuations in drive train caused by wind turbulence and to allow more efficient operation in variable and gusty winds • Now: onshore wind turbine with rated capacity over 2 MW use variable- speed wind turbine system
    35. 35. Application: offshore wind power  The first offshore wind power plant was built in 1991 in Denmark, consisting of eleven 450 kW wind turbines  1. 2. 3. Advantages of offshore wind energy minimal environmental impact large areas available for wind farm development wind speed are higher  Variable-speed direct-driven wind turbines using PMSG meets the offshore wind farm requirements: 1. High turbine power capacity 2. High reliability 3. Maintenance free
    36. 36. Mitsubishi Heavy Industries Wind Power Technologies J. Roney, “Offshore Wind Development Picking Up Pace,” 22 August 2012. [Online]. Available: http://permaculturenews.org/2012/08/22/offshore-winddevelopment-picking-up-pace/. [Accessed 18 November 2013]
    37. 37. 6. Conclusion & Future Directions
    38. 38. R. Wiser, Z. Yang “wind energy,” 2010. [Online]. Available: http://srren.ipcc-wg3.de/report/IPCC_SRREN_Ch07.pdf. [Accessed 18 November 2013]
    39. 39. The future Development of offshore wind farm Improve the efficiency Increase the reliability manage the high level of wind energy penetration to the utility grid to meet the grid code Development of power electronics to lower the cost
    40. 40. Full Scale Converter for Synchronous Wind Turbine Generators Thank you!

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