Uhhhh Martin Senior . . . single phase is single phase regardless of voltage. The 220Volt AC voltage in your circuit breaker panel at home yields a single phase-to-phase 60 Hz sinewave. It looks the same as the sinewave that you get when you go from one phase leg to neutral to yield 110V except that it has twice the amplitude - which by new math and old math = 220V.
The AC is stepped down through a single phase transformer and run through a big honking (technical lingo for High Current capacity) diode bridge. :p This is typically a full bridge diode device that gives a DC waveform with a 60Hz ripple.
A 3-phase source has a 120 degree ripple with a higher RMS voltage value due to the fact that the peaks of the summed sinewaves are only 120 degrees apart (5.55 msec) vs being 360 degrees apart (16.67msec). You could smooth the ripple using big honking bus capacitors, but I don't think they do that because they would source so much current when you struck an arc that it would blow a hole in your metal or vaporize your rod - in other words, you would need a big honkin inductor to limit the current surge at the welding arc and this would need to be adjustable and bla bla bla - ie it is easier to simply run with a diode bridge and the 60Hz ripple or 120Hz ripple . . . in the end, you have to ask yourself, does the arc really care? I don't think so. . .
The big advantage of 220V is that you pull 1/2 the line current to get the same amount of weld current. You have less of a copper mine in the box for the same duty cycle . . . but beings copper is cheap, you typically have the same amount of copper but twice the duty cycle. . .
Advantage of 110volt wirefeed? Plug it in anywhere just about . . . typically smaller because duty cycle is less . . . cheaper, etc.
But like a chainsaw or an aircompressor. If you plan on using it regularly on a broad range of applications . . . bigger is better!
