In the 1970s and 1980s there was much more variety in wind turbine design. There were two bladed machines, multi-blade ducted turbines, Darrieus rotors, and other exotic technologies. Outputs were in the 50KW range. Pacheco Pass in Northern California had examples of most of those. Some didn't work too well. Loss of blade accidents were common in the early days, with blades thrown considerable distances.

The three-bladed machines won out commercially. Machine size went up because output vs cost decreases with size, at least up to 1-2 MW. Lots of little machines were a pain to install and maintain.

Wind generators used to be AC generators synchronous to the grid. But with higher power semiconductors available, putting a big AC-DC-AC converter on the output to sync it to the grid is becoming popular.[1][2] This allows generating some power during low-wind conditions, and provides much more adaptability to wind gusts. When the wind speed changes, the blade pitch is adjusted to compensate, but on big turbines, this takes tens of seconds. Being able to adjust electrically in milliseconds avoids power grid transients.

The push for permanent magnet motors in wind turbines is more about converting to direct drive and getting rid of the gearbox. Wind turbine gearboxes are a huge pain, wearing badly for reasons that were only understood in the last few years.

[1] http://www.theswitch.com/wind-power/ [2] http://new.abb.com/motors-generators/generators/generators-f...