Direct drive and other advanced
generators
Dr.ir. Henk Polinder
Electrical Power Processing
Delft University of Technology
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Content
• Introduction
• What did we do and why?
• What are our plans?
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Currently used
generator systems
Constant speed with gear (CS)
–Squirrel cage induction generator
–Stall control
–Up to roughly 1.5 MW
Variable speed with gear (DFIG)
–Doubly-fed induction generator
–Pitch control
–From roughly 1.5 MW
Variable speed direct drive (DD)
–Synchronous generator
–Pitch control
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Power electronic converters
- Standard component
- No research in design
- Some work on control
(grid requirements Morren)
+
_
u1
u2
Ud
u3
u4
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Comparison of generator systems
- To determine what is the most suitable generator system
- Criteria: cost and energy yield
- Focus on large wind turbines
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Design of direct-drive generators
• Hardly improvements possible in induction generators
– Improvements possible in power electronics
• To eliminate gearbox:
– Losses, maintenance,
failures
• Improvements possible
in direct drive
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Direct drive generator types
Electrical excitation PM excitation
Generator cost (KEuro)
447
312
Annual energy yield (GWh)
7.88
8.04
Active material weight (ton) 46
24
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Generator winding types
Full-pitch distributed
winding
-Well-known
-Hardly space harmonics
Fractional pitch
concentrated winding
(modular)
-Cheaper
-Significant space
harmonics
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Transverse flux generators
• simple stator winding
• high force density
but
• reduced force density
for larger air gaps
• complicated mechanical
construction
• low power factor
flux
coil
magnet
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Further research
• Cheaper generator types
– Cheaper windings
– Transverse Flux PM generators
• Magnetic bearings
– Maintenance-free
– Reducing mechanical loads because of flexibility