Re: An actual design question...

On Sat, 31 Jan 2009 09:37:32 -0800, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

JosephKK wrote:
On Tue, 27 Jan 2009 17:09:37 -0800, "Joel Koltner"
<zapwireDASHgroups@xxxxxxxxx> wrote:

"Joerg" <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:UVNfl.14366$yr3.4334@xxxxxxxxxxxxxxxxxxxxxxx
Well, yeah, it'll run. All I can tell you that I ran quite a few smaller
motors on modified sine and none of them was too happy about it. Heat wasn't
a huge issue but reduced power was.
Do you know why?

Years ago in a power electronics class that I took we did various SPICE
designs of motor controllers, and while we just generated "modified" square
waves, the inductance of the modeled motors made the output waveforms look
*very* nice.

AFAIK most motor controllers use modified square waves?


Naw. All the better ones use PWM to induce sinusoidal currents. With
all the added circuitry that entails. Especially VFDs.


The added circuitry actually isn't all that much. You need a half- or
full-bridge converter before the communtation bridge anyhow. All you
have to do is modulate the pre-converter with a sine. Either from a
table or, if the last penny counts, from an oscillator. Of course, to do
a thorough job you wouldn't be able to play the usual trick to add the
output onto the incoming DC-voltage in order to save a few pennies in
copper.

Most significant to serious VFDs are 3-phase input and output. Some
of the single phase assumptions don't work for them.

.