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

[Peter Gottlieb]

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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