I think there could be. There are different aspects to using the motor with a VFD (putting operation at above rated speed to one side):
1. the increased stress on the insulation because of high voltage transients (as a result of fast pulse rises times giving reflections at either end of the cable) - mitigated by using special enamel coatings for the winding etc.
2. possibility of bearing currents - mitigated by insulated bearings etc.
3. increased losses in the machine primarily due to current harmonics - mitigated by reducing the rating compared to a motor working direct on line.
You could say that a inverter-capable motor need only deal with 1. and 2., whilst the inverter-duty motor deals with all three.
There are no standards for these terms so you need to read the fine print in the specs carefully. I've seen Inverter Duty, Inverter Rated, and Inverter Ready, all with no hint of what the term means.
Be careful. The marketing people are running amok on these terms.
The only Spec. which really covers an inverter duty motor is IEEE841 spec, which is the Best Severe Duty motor, since their is no legal definition or one by NEMA. Standard EPACT motors may be used if the insulation is good enough to stand the spikes and transients, which may be produced by the drive, and if the runs are short in length. Cooling is one of the factors, since the fan will turn at less RPM, giving less CFM of air movement to disipate the heat. Also as was said earlier if one of the bearings is insulated, then there are no shaft currents to ruin the bearings.
NEMA MG-1 Part 31 deals with Definite Purpose Inverter Duty motors. When we specify motors, we use ask that the motor be built according to the standards of NEMA MG-1 Part 31 in an effort to quantify what we mean by inverter duty.
