F1technical.net

http://pdf.sumobrain.com/US20170350315A ... #view=FitH

This looks like it's for keeping the turbine spooled and in an efficient range by motoring the MGU and is also capable of generating. I didn't see anything in there for turbo compounding, though.

The fact that it requires a VCT on the intake side is a HUGE clue as to how the current power units work. There isn't just variable trumpets, but variable inlets, and variable manifold pressure, and all of these can are used to tune combustion properties to favor regeneration or deployment.