1. Basic Operation Principles and Electrical Conversion Systems of Wind Turbines
H. Polinder, S.W.H. de Haan, J.G. Slootweg, M.R. Dubois
Norpie, June 2004
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2. 1 Introduction
Environmental concern
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3. 1 Structure Introduction Basic relations Often used generator systems
Alternatives and trends
Conclusions
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4. 2 Basic relations: power coefficient
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5. 2 Power curves
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6. 2 Stall principle
Increasing wind speed > increasing angle of attack
Blade design so that at rated power the airflow becomes loose from the blade > eddy’s
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7. 2 Energy yield
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8. 2 Rated speed
Rated speed limited because of noise production by blade tip speed:
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9. 2 Generator dimensions
For direct drive:
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10. 3 Generator systems Constant speed Squirrel cage induction generator
Stall principle
Variable speed with gear
Doubly-fed induction generator
Pitch
Variable speed direct drive
Synchronous generator
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11. 3 Generator system with gear example
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12. 3 Direct drive generator example
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13. 3 Output power of generator systems
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14. 3 Comparison of generator systemsCS
DFIG DD
Cost, size and weight +
+/- -
50/60 Hz grid frequency
Audible noise of blades
Energy yield
Variable speed
Gearbox
Generator
Converter
Reliability and maintenance
Brushes
Mechanical loads
Complexity
-(PM+)
Power Quality
‘Flicker’
V&f control
Harmonics
Grid faults
fault currents
restoring voltage
3 Comparison of generator systems
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15. 4 Alternatives Squirrel cage induction generator with converter
+ Brushless generator
+ Cheaper (IG) generator
+ Grid fault ride through capabilities
- More expensive converter
- More converter losses
Brushless synchronous generator with converter
+ More efficient generator
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16. 4 Trends in geared generator systems
Towards variable speed
Hardly development in doubly-fed induction generators
Development in converter performance during grid faults
Brushless synchronous generator?
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17. 4 Trends in direct drive systems
Unique machines:
low speed
high torque
limited efficiency
Induced voltage
Resistive voltage drop
> Interesting research field!
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18. 4 Trends in direct drive systems
From electrical to permanent-magnet excitation
lower losses
significant reduction in active mass
reduction of magnet cost
Not from radial to axial flux
axial flux may be smaller
but axial flux is heavier and more expensive
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19. 4 Trends in direct-drive: transverse flux?
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20. 4 Trends in trends in voltage levels
The current voltage level is mostly V
Windformer ABB
Zephyros: kV
NEG-Micon (VTDI) stator: 6 kV
Expected: trend to several kV to limit losses
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21. 5 Conclusions Trend towards variable speed
Geared and direct-drive turbines will remain both
Radial flux permanent-magnet machine most suitable for direct-drive
Rise of voltage level up to several kV for large turbines
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