Does Soft Starter generate harmonics like VFD?

Soft starters also create huge RFI and harmonics at start, though when the motor(s) they are applied to reach operating speed, they essentially disappear. This is due to soft starts using SCR's, and when they are firing at the beginning, then basically at the end of the cycle when the motors are slowed and stopped. I think a great example of this is a dimmer switch on something as simple as indoor lighting, as it basically works on the same principle as an SCR. If you have an AM radio near the dimmer, when you turn it up you'll hear the interference in the radio, until the dimmer motion stops. By the same token, when you dim the lights the interference will again be noticeable until the switch stops or is of course turned off.

Variable frequency drive (VFD), unlike soft starter, generates sinusoidal wave form output continuously. Soft starters obviously do not generate wave form output, and as such the distortions they create are not continuous as with VFD operation. But, there are several means to keep what causes the distortion in check, including use of RFI filters on the VFD output, AAF (advanced active filters) and passive filters that are available and reduce distortions to 5%.