[ARC5] Fwd: Smart People: 60Hz Transformers Faster?

[Dennis Monticelli]

I will second what Peter is saying.  My lab at work studied VFDs and built
protos of advanced types.  Most VFDs are relatively low in frequency (sub
100KHz) and do rely on the motor inductance to smooth the energy flow
(motors do prefer sine waves).  EMI filtering of VFDs is usually
elementary.  Filters for a 20KHz drive are large and costly so shielded
cable suffices.  Their are new drives coming to the market that are
switching at higher frequencies (100KHz or greater), which shrinks the bulk
and cost of LC filtering to the point that such filtering is included.  I
seriously doubt anything out of China is going to feature this; expect lots
of hash on the raw output.

Dennis AE6C



On Tue, Nov 24, 2015 at 6:08 AM, Peter Gottlieb <nerd at verizon.net> wrote:

> All VFDs synthesize their output. The high frequency pulses are smoothed
> by the motor winding inductance. There can be quite high voltage spikes on
> the cable which is why there is special VFD cable. If you are going to use
> a VFD as a power source you should use a reactor in series with the output
> and then capacitors to ground (or other legs, If delta) to smooth and
> filter. These are pretty commonly available but you need to do the math for
> your application to find the most appropriate values. If you look into
> inverters (such as line interactive solar ones) you will see this exact
> kind of output filtering. Once so filtered, you'll get a decent sine wave.
> In the US, line connected inverters must have less than 5% THD, in the EU
> less than 3%.  That's with the simple LC filter from a PWM output.
>
>
> Peter
>
> > On Nov 24, 2015, at 8:48 AM, Tom B <tbryan at nova.org> wrote:
> >
> > Robert,
> >
> > I did a little more reading about VFDs in general and learned that these
> > put out PWM and nothing like a sine wave.  I don't think this will work.
> >
> > Tom
> >
> >
> >
> >> And notice that it is claimed to go down to DC (0 Hz).  :-)
> >>
> >> Tom, the output is 3-phase (I couldn't figure out whether it is Delta or
> >> Wye).  Dave didn't say whether his load requirement was single or
> 3-phase
> >> but
> >> that usually implies single phase.
> >>
> >> Not pertinent to the original subject, but the eBay writeup is some of
> the
> >> worst Chinglish I have seen in recent years.  Usually they do a little
> >> better.  Good luck getting it hooked up and working.
> >
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