Wind turbines, the big ones, regulate themselves to turn in sync with the grid. The adjust thier blades as needed to keep pace/power. That's why huge fields of them all turn in perfect lockstep.
From some random reading on the net, it is the smaller ones that can be directly connected. Above 2MW things are not as easy and it is better and more efficient to convert to DC.
* Choosing pitch angles for efficiency and turbine safety. You can, for smaller turbines, just synchronize the turbine to the grid, but this is becoming uncommon practice.
* Converting the produced AC power to DC, and then choosing the proper frequency output and voltage to feed power to the grid, and inverting the DC to make this power. This should usually be trying to "speed up" the frequency of the grid a little if it's not already way too fast and regulate the voltage appropriately.
The second link you have, on page 3, shows (active) rectification (d) of the wind turbine AC power to make positive and negative DC buses, and then inversion of that DC (f) to make 3 phase AC output power.
Yeah, I don't know if for example in big wind offshore wind parks, since it's connected with a DC cable to mainland anyway, you would convert all the turbine generator outputs just to DC.
Then at the ground station where it's connected to the grid, convert to AC, whatever kilovolts are needed.
> you would convert all the turbine generator outputs just to DC.
You could. But you probably still need a DC/DC conversion step or boosting in order to let the power flow from each of the turbines fairly. (The synchronous conversion to DC from AC provides opportunity to slightly change the voltages you get out, but not terrifically so).
Yup, that's why the word "safety" is in there. I probably could have put that better. (It also includes e.g. feathering rather than just trying to stay close to rated power, speed, and torque limits)
> "That's why huge fields of them all turn in perfect lockstep."
Not true for any modern wind farm. While they might appear to be turning together, that's just because the wind conditions are relatively consistent across the whole area. Not because they are actually synchronised! Most modern turbines will target a certain rated/optimal/maximum rpm once a certain wind speed has been reached, but are free to rotate more slowly (while still generating power) in light wind conditions.
They wouldn't necessarily need to do 50 rounds per second to generate 50 Hz. There could be any number of poles on the generator. At least in theory... Not saying you're wrong about not being synced but just that they wouldn't need to do 50 rps...
Gearboxes. Windmills of the same design will turn at the same rate in lockstep with each other. A gearbox converts that rate into what is necessary for the generator. The generator turns in sync with the grid.