OK.
Perhaps you'd care to offer your explanation, in your own words, of how a forward biased diode can put energy back into the supply.
Single Phase current draw for a 3 phase output VFD: technical discussion
- Thread starter Jraef
- Start date
- Status
Perhaps you'd care to offer your explanation, in your own words, of how a forward biased diode can put energy back into the supply.
PFC caps improve power factor by exchanging energy with the load... not the supply. If the capacitor(s) exchanges energy with the supply, it is overcorrecting the motor load power factor. You end up with a power factor less than 1 but with current leading the voltage rather than lagging.
In the case of a VFD, the active electronics of the PWM-inverter stage switch between the DC rails to facilitate the capacitor-inductor energy exchange... but it goes unnoticed because of the output frequency and PWM waveforms.
The supply is the common source/sink.
Could you kindly explain, in your own words, how a diode rectifier can put energy back in the supply which is what I politely asked?
If you can't, that's fine too.
We can agree and move on.
I can, but I won't
it is covered in depth in mant text on power electronics
you can research it and study it at your own pace and math level
the bottom line
vfd's improve line pf
rectifiers and igbt, etc, bidirectionally flow Q
larger vfd caps improve pf further
in my black box example
starter/pfc caps vs vfd
absolutely no difference in measurable and observable results
I am so astonished...................that you would decline such a golden opportunity to share your brilliant grasp of power electronics yet denigrate my claims on the subject..
How about you tell us a little about your most recent design/install?
Last edited by a moderator:
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Guys,
As this descends further into acrimony (I don't care where from), I am closing the thread. As I said a while ago now, I am in agreement with the concepts put forth here on how the non-linearity of the principals involved make it difficult to nail this down into any exactitude, but I think we can all agree that attempting to size a VFD for a single phase feed at anything LESS than 2X the motor current rating is a recipe for trouble. THAT was the initial point of this thread; being able to give electricians, usually left with the responsibility for sizing circuits, a simple guideline for making a good choice and I feel it has been sufficiently addressed. I for one have NEVER used the 1.732 model for this purpose, but I do see it used quite often, especially in websites and by some "less than helpful" drive purveyors. That was why I brought it up, so it could be aired out and have the light of intelligent minds shine on it. So I think this thread has successfully accomplished that.
Need we go on trying to convince one another of side details to the point of acrimony? I think not.
As this descends further into acrimony (I don't care where from), I am closing the thread. As I said a while ago now, I am in agreement with the concepts put forth here on how the non-linearity of the principals involved make it difficult to nail this down into any exactitude, but I think we can all agree that attempting to size a VFD for a single phase feed at anything LESS than 2X the motor current rating is a recipe for trouble. THAT was the initial point of this thread; being able to give electricians, usually left with the responsibility for sizing circuits, a simple guideline for making a good choice and I feel it has been sufficiently addressed. I for one have NEVER used the 1.732 model for this purpose, but I do see it used quite often, especially in websites and by some "less than helpful" drive purveyors. That was why I brought it up, so it could be aired out and have the light of intelligent minds shine on it. So I think this thread has successfully accomplished that.
Need we go on trying to convince one another of side details to the point of acrimony? I think not.
- Status