I am looking for info on Variable Geometry Turbochargers. I'd like to know how they are conrtolled as well as how various engine parameters are calculated into the resulting position of the VGT.

 

The vanes are adjustable to control the amount of exhaust that is induced on to the turbine; basically changing the A/R under varying load conditions. One advantage of this is that it allows the compressor to build more boost under low engine speeds and can eliminate the need of a wastegate.

Hydro-powered generators have been using this technology for many years to control the output of a generator.