in phase controlled converters, the maximum voltage
applied to motor may be as high as the   maximum value of the ac supply*  when firing angle less than  90 deg which is quite usual.
*(phase to neutral or phase to phase  depending on the type of converter and the converter transformer secondary voltage if exists)
  Modern motors are generally produced as to be fed from
converters and insulation strength can tolerate voltages
higher than  nominal armature voltage .

 A worn or older motor may not handle such voltages especially in three phase  fully contolled case

my solution proposal is that: if you not sure of the insulation strength of your  motor,  use  a transformer
in order to fix maximum value of the applied voltage
to the %110 of nominal armature voltage of the motor and
contol motor speed by triggering delay angle.
Another important note is on power factor issue,
if you need to create greater delay of the trigerring angle, your power factor would be as poor as cos(alpha)
by
more question ? >>atadur@hotmail.com     

Suggestion: The DC bus may need an additional treatment, e.g. filters, transient voltage suppressors, etc.
Alternate products, e.g. ABB DCS 400, etc., might be checked.  ABB claims that the IGBT switching increases carbon brush lifetime. Autotuning for armature and field currents could be found useful.