The blade angle is adjusted to get optimum power extraction. Rotor RPM is completely independent of produced power frequency.
References: https://www.vestas.com/en/products/offshore/V236-15MW and https://library.e.abb.com/public/bf09cdf11d234241845c79ac343...
The electronics perform two key functions:
* 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.
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.
