RFI vs Harmonics using VSD's

RFI is Radio Frequency Interference.

Harmonic interference from drives starts at a much lower frequency, and the frequencies involved are all numerically related to either the drive output frequency or the switching (carrier) frequency.

RFI could be anything above, say, 100kHz or so. It would not necessarily have any relation to the drive output or switching frequencies, and could be a local radio ham's transmitter, or the steelworks down the road, among many, many other possible culprits.

Watch out if you have arc welders on either directly on your supply or on your system ground - you will experience noise from DC up into the broadcast bands. (This week has been a bitter reminder!)

RFI is what happens when your harmonics extend into the frequincy band of something else like a radio, TV or Hi-Fi, and get into the circuitry.