Will have a go at answering it for nothing other than a bit of debate stimulation!

Having run generation plant driven by diesel, gas turbines and now wind turbines, I hope to be at least half in a position to pitch in something of worth!

As more and more wind generation penetrates the UK grid, then the control systems implemented become more and more sophisticated.

An "old" induction generator wind turbine really had no control - It produced whatever the wind was fit to drive it at. If system frequency rose or fell, the turbine would run slightly faster, or slower, accordingly, without any change in power output. A simple system of power factor correction, allowed simple changes to power factor, but always leading.

Most modern wind turbines now use dual fed induction generators, with the stator directly grid connected, and the rotor, inverter fed. This permits the generator to run at variable speed, whilst still "hard wired" to the 50 Hz grid. It also allows a broad range of control functions, including running at leading or lagging power factors or running in voltage support / suppression modes, amongst others. Coupled with Statcoms (or Static Var Compensators) which are more commonly being applied on remote windfarms where the grid is weak, and pitch regulated turbines, which can reduce or increase their output on demand from a remote telemetry system, then the modern wind turbine is very versatile!

How they are controlled depends entirely on how the grid connection is managed. Some windfarms now have very tight limits to operate within, and this can be varied on an hour by hour basis, even remotely, depending on grid requirements - In all, not vastly different from the controllability of a conventional power station!

New and innovative methods of operating grid systems, such as the Registered Power Zone in Orkney, seek to explore ways of increasing utilisation of embedded generation, including wind turbines, and this is releasing additional capacity in a previously "full" grid, by implementing innovative diversified control systems that ensure the embedded generators are as much a key part of controlling the system as the conventional, centralised generation.

Hope this helps answer the original question without too much waffle!

Cheers

Bryan
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Bryan Rendall