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I am currently studying wind power and the power electronics used for it. In wind power a generator is driven by wind, thus the resulting power is of widely varying frequency and amplitude. The power grid, in turn, has strict requirements for the input power in terms of frequency, phaseshift and sinusoidal form. For this reason, power converters are today used routinely in wind power.

The predominant way to get the power into the grid is to use an AC-DC converter followed by a DC-DC converter and a DC-AC converter. This seems rather complicated instead of using a single direct AC-AC converter. Why is the indirect conversion via the DC "in-between" route preferable?

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  • $\begingroup$ Usually the power generated by wind turbines are not directly ready to use, so we need to transport and integrate it into the interconnect networks. That's why the DC net is used to transport the power. HVDC is the most efficient way to transport electrical power. Another reason is, we have enough harmonics in the net so we need to filter them out. $\endgroup$ Jul 25 '19 at 22:56
  • $\begingroup$ @SamFarjamirad: Actually, the question is about the standard AC power grid. AC power is not AC and needs to be transformed to be suitable for grid use. The question regards how this is done and why the standard way to do this employs a DC step inbetween. $\endgroup$
    – ckrk
    Jul 25 '19 at 23:00
  • $\begingroup$ When 2/3 of it (and it's cooling system) no longer needs to be 180 meters in the air on a pole? To combine multiple turbines on a single DC bus? $\endgroup$
    – Phil Sweet
    Jul 27 '19 at 1:03
  • $\begingroup$ @PhilSweet: Tanks for your comments! Especially, the 2nd makes a lot of sense to me, that the intermediate DC allows to collect inputs of several turbines, witch seems a frequent case for wind farms. Regarding, the 1st comment, i believe that the power electronics are typically situated on the ground. Stil, what would be the disadvantage of having AC/AC conversion 180 above ground? Are you implying that it is heavier to buil a direct AC/AC system? $\endgroup$
    – ckrk
    Jul 27 '19 at 11:16
  • $\begingroup$ Now cross posted here : electronics.stackexchange.com/q/450383/152903 $\endgroup$
    – Solar Mike
    Jul 27 '19 at 12:10
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The wind turbines that I have worked on, and others I have read about, rotate the generator at the correct speed to produce the power at the correct voltage and frequency so it goes directly into the grid.

This is why they control the pitch of the blades to keep with the tolerances stated by the power supply companies for voltage and frequency...

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    $\begingroup$ there are several concepts on how to attain grid stability. The one you describe is probably the classic approach, however it is getting less common. Modern wind turbines tend not to pitch for grid stability anymore, but pitch only to stay in the optimal power conversion regime mandated by tip-to-toe ratio. Thus they maximize power output and use power electronics to ensure grid stability. $\endgroup$
    – ckrk
    Jul 26 '19 at 9:32

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