Wind Turbine Technology

Wind turbine control concepts

Aerodynamics of a wind turbine blade

Stall

Wind turbine blade aerodynamics - stall control.jpg

Stall Control:
– Passive Stall:
Power of the wind turbine is limited by the aerodynamic characteristics
of the turbine.
– Active stall:
Power of the wind turbine is limited additionally by decreasing the pitch
angle (increasing the inflow angle ).

Pitch

Aerodynamics at a wind turbine blade during control through pitching

Pitch Control:
– Power of the wind turbine is limited by increasing the pitch angle
(decreasing the inflow angle $\alpha$)

Wind turbine operation

Operation of Fix Speed Wind Turbine (passive stall)

• Start up (with open breaker) if wind speed > cut-in wind speed
• Close breaker
• Operation at constant blade angle over the whole wind speed range
• In case of large wind speeds: Power limited by aerodynamic profile.

Operation of Variable Speed Wind-Turbines

Start up (with open breaker) if wind speed > cut-in wi

Typical power curves of wind turbines.jpg

nd speed
• Close breaker

• Below rated wind-speed
– Maximum power coefficient (Max. Power Tracking)

– Evt: Speed Limitation
• Above rated wind-speed:
– P=Pr
ated (Limited by power electronics converter)
– Pitching

• Advantages of variable speed operation:
– Lower cut-in wind speeds
– Higher efficiency, especially at low wind speeds
– Lower power variations (compared to fixed speed turbines)
• Disadvantage: More expensive!

Generator concepts

Fixed Speed Induction Generator

Fixed speed induction generator.jpg

Only fix speed operation possible (stall control required)
• Reactive power compensation required
• No reactive power control capability. Additional devices required:
– TSCs (Thyristor switched capacitors)
– STATCOMs
• Risk of dynamic voltage collapse
GTZ Expert Workshop 2010: Grid and System Integration of Wind Energy, 22/23.11.2010, Berlin/Germany
y g p
– > Typically, wind generators based on induction generators are asked to
disconnect in case of voltage dips

Induction Generator with Variable Rotor Resistance

Induction Generator with Variable Rotor Resistance.jpg

Simple concept for variable speed operation.
• Reactive power compensation required.
• No reactive power control capability. Additional devices required:
– TSCs (Thyristor switched capacitors)
– STATCOMs
• Limited LVRT capability. Dynamic voltage collapse problems have to
GTZ Expert Workshop 2010: Grid and System Integration of Wind Energy, 22/23.11.2010, Berlin/Germany
be mitigated by:
– Fast increase of rotor resistance during faults
– Additional reactive power compensation devices (typically TSCs)

Generator with fully rated converter and direct drive

Directly Coupled Synchronous Generator with Variable Gear Box