Re: VFD ?

> I understand a VFD rectifies line voltage to DC then inverts it at the
> required frequency. My question is how it then inverts the DC. Is this a
> chopped voltage like a pulse width modulation to build the AC wave form?

Everything today is some sort of high frequency switching design of
varying degrees of complexity. The best designs almost certainly use
the "Magic Sine Wave" principle, as espoused by Don Lancaster.

> Or
> does it generate varying DC levels? I would suspect the former but do not
> know.

The "analog" scheme has been employed in commercial products, although
I've not seen it for some long period of time.

This old-fashioned idea actually does enjoy an advantage over the switching
designs in one very narrow respect - not all motors are happy about being
fed high frequency signals. ( Motor manufacturers are starting to list
motors as being VFD capable )

It has the horrible disadvantage of being tremendously inefficient. But it's
a simple design conceptually: three BIG Hi-Fi amplifiers fed by an oscillator.

Alan


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Alan Rothenbush | The Spartans do not ask the number of the
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