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. Agenda
1.
2.
3.
4.
5.
6.
Introduction – The Evolution of modern WT
Characteristic
Design
Control
Application
Conclusion – The Future

3. 1. Introduction – The evolution of WT

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. 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. 2. Characteristic

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. 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. 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. 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. 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. 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. 3. Design

14. Design of a Gearless Wind Turbines (Enercon)

15. Variable Speed WECS - Configuration
70%
Any types of
Generator

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. 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. Harmonic distortion - Comparison
Next topology
Back-to-Back VSI

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. 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. Multi-Level Converter
Create a sinusoidal high voltage output from several levels of voltage

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

24. Integrated gate-commutated
thyristor (IGCT)

25. Integrated gate-commutated thyristor (IGCT)

26. 4. Control

27. 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

28. 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

29. Full Scale Converter

30. 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

32. 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

33. Non-salient Generator: Zero d-axis Current Ld = Lq

34. Salient-pole Generator: MTPA : Ld < Lq

35. 4. Application

36. 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

37. 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

38. 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]

39. 6. Conclusion & Future Directions

40. R. Wiser, Z. Yang “wind energy,” 2010. [Online]. Available: http://srren.ipcc-wg3.de/report/IPCC_SRREN_Ch07.pdf. [Accessed 18 November 2013]

41. 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

42. Full Scale Converter for Synchronous
Wind Turbine Generators
Thank you!