Why use a double fed wound rotor induction generator in wind turbines?

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cai
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With large wind turbines which have AC generators why do they convert from AC to DC and then back to AC before connecting to the grid, why not just connect straight from generator to the grid without converting? Very confused please can someone explain!
 
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In order to connect to the grid the voltage, frequency and phase would have to closely match that of the grid. How would you accomplish that?

Frankly I have wondered why they couldn't use a DC generator, but instead of a DC field on the generator, connect the field coil to the grid at the right phase to produce an output in phase and at the same frequency as the grid.
 
skeptic2 said:
In order to connect to the grid the voltage, frequency and phase would have to closely match that of the grid. How would you accomplish that?

Frankly I have wondered why they couldn't use a DC generator, but instead of a DC field on the generator, connect the field coil to the grid at the right phase to produce an output in phase and at the same frequency as the grid.

Skeptic - check out "double fed wound rotor induction generator" it's mighty close to what you described.

http://www.tecowestinghouse.com/PDF/DF_WR_Induction_Generator_Flyer.pdf

http://www.labvolt.com/downloads/download/86376_f0.pdf