Try here first :
You will need to excite the field first, but that is already happening if you have been running and are now going into coastdown.
All About Circuits usually has good answers as well
The chart 3/4 of the way down the page should be what you're looking for.
For those looking for the simple / practical answer, when the voltage applied to the stator is les than the syncro speed the shaft is turning, there will be induced current back into your controller. Be carefull, quickly lowering the "drive" voltage is like slamming on the brakes. Think "downshifting" with your voltage curve.
Just reread your origional post. Yes, they are just self excited syncro motors, the language is screwing with you.
Where you went wrong is that with ACIMs, negative slip induces current not consumes it.
Google "induction braking" as well for formulas on how much you will need to absorb/dissipate.
