In theory, driving one is a easy.
You put some current through the field winding, then by controlling the voltage applied to the main winding (well actually armature), you control the speed.


The 150VDC is the easy bit, and could probably be done using something like a suitable KBIC SCR drive that could control the current.
The issue is the variable 400VDC at up to 20A needed to provide motion.

SCR drives are pretty common, but normally limited to a couple HP, as their main use now is basic speed controllers running from single phase.

You could possibly get away with one small SCR drive set to give the required field current (the current control is more important than the voltage), then use another 240VACinput/180VDCoutput SCR drive for the armature, but that would limit the possible speed, to under half the rated speed.

There is also aspect that reducing the field current/strength increases speed for any given armature voltage, so it's a bit of a juggling act.
I think in normal use, whoever specifies/installs the motor will decide what speed they'd like, and will fix the field current to give their desired operating speed.