Ideally? Really? I'd say that's along with the rest is a given. What we want is a numerical basis for choosing a properly sized VFD. I believe everyone participating here knows that a properly sized 3Ø VFD connected to 1Ø supply can power a 3Ø motor. Let's identify the characteristics that affect the "properly sized" aspect of choosing a VFD rather than saying this depends on that without being any closer to decision parameters.
Single Phase current draw for a 3 phase output VFD: technical discussion
- Thread starter Jraef
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gar
Senior Member
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- Ann Arbor, Michigan
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- EE
170527-1200 EDT
Smart $:
The original thread was about using an existing 3 phase VFD, motor, and fan in a new application that only had single phase available, and the new application was different than whatever the VFD system had been originally ordered for. Question was could it be used. The question was not about buying a new VFD.
Very early on in that original thread Jaref and I suggested the diodes and capacitor were probably the limiting items. Jaref considered the capacitor as probably the more important limiting factor. I think I might now agree, whereas originally I was probably more on the diode side.
For wharever reason, probably the title of this thread, this thread has not had much discussion on the real question of the original thread.
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Smart $:
The original thread was about using an existing 3 phase VFD, motor, and fan in a new application that only had single phase available, and the new application was different than whatever the VFD system had been originally ordered for. Question was could it be used. The question was not about buying a new VFD.
Very early on in that original thread Jaref and I suggested the diodes and capacitor were probably the limiting items. Jaref considered the capacitor as probably the more important limiting factor. I think I might now agree, whereas originally I was probably more on the diode side.
For wharever reason, probably the title of this thread, this thread has not had much discussion on the real question of the original thread.
.
We are not in that thread, nor is the discussion about that thread. Please read post #1 in this thread: http://forums.mikeholt.com/showthread.php?t=184232&p=1831574#post1831574
gar
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- Ann Arbor, Michigan
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- EE
170527-1500 EDT
Why should an AC to DC power supply designed for 3 phase input with a 0.95 power factor at full load be expected to still have an 0.95 power factor at any load when supplied from single phase?
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Why should an AC to DC power supply designed for 3 phase input with a 0.95 power factor at full load be expected to still have an 0.95 power factor at any load when supplied from single phase?
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the vfd will impact line pf
usually improve it due to the pwr sup caps
the output is determined by the motor and vfd firing angle of the inverter
gar
Senior Member
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- Ann Arbor, Michigan
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170527-1853 EDT
Smart $:
Power factor is only meaningful as applied to a two terminal load. The definition is PF = W/Eeff*Ieff from "Analysis of AC Circuits", p 28, Melville B. Stout, Professor of Electrical Engineering, University of Michigan, 1952.
A quote from Stout on p 28 "From a laboratory standpoint, power factor is the same for distorted waves as for pure sine waves -- it is the quotient obtained by dividing the wattmeter reading by the product of voltmeter reading by ammeter reading." Obviously from my first paragraph RMS values are implied.
One can extend the definition of power factor from a two terminal device to a balanced three phase load if appropriate voltage and current measurements are used.
The input power factor to a device or system that goes from AC to pure DC and then to something else as the final load were the DC load power and voltage are constant, and that final load has an arbitrary power factor will not have its input power factor affected by the final load power factor. That constant DC bus isolates the input power factor from the final output factor. However, changing the DC load power can change the input power factor.
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Smart $:
Power factor is only meaningful as applied to a two terminal load. The definition is PF = W/Eeff*Ieff from "Analysis of AC Circuits", p 28, Melville B. Stout, Professor of Electrical Engineering, University of Michigan, 1952.
A quote from Stout on p 28 "From a laboratory standpoint, power factor is the same for distorted waves as for pure sine waves -- it is the quotient obtained by dividing the wattmeter reading by the product of voltmeter reading by ammeter reading." Obviously from my first paragraph RMS values are implied.
One can extend the definition of power factor from a two terminal device to a balanced three phase load if appropriate voltage and current measurements are used.
The input power factor to a device or system that goes from AC to pure DC and then to something else as the final load were the DC load power and voltage are constant, and that final load has an arbitrary power factor will not have its input power factor affected by the final load power factor. That constant DC bus isolates the input power factor from the final output factor. However, changing the DC load power can change the input power factor.
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junkhound
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Is the discussion getting deep enough to start discussing negative, positive, and zero sequence math methods of analyzing 3 phase circuits?:huh:
Or delving into PFC boost circuits and why to get < 0.1% THD and 99.9+ PF only single phase at a time can be rectified (not counting Vienna bridge circuits) and boosted ? :blink:
Just asking :roll:]
Or delving into PFC boost circuits and why to get < 0.1% THD and 99.9+ PF only single phase at a time can be rectified (not counting Vienna bridge circuits) and boosted ? :blink:
Just asking :roll:]
Does starting a discussion of these concepts contribute anything to the original query? If yes, have at it.
OK, here's the model
480/1 in, 480/3 out, 200 HP motor load to 90%
starts under full load, ramps 1200 rpm/sec
took some time to detail the drive parameters, diode characteristics, snubber values, internal R, etc.
also to come up with the control system parameters, gains, etc., used speed control, but torque control can be configured also
bear in mind S is used, not P
S power in/out ~1.084, 8% losses
I in / I out ~ 1.88 (includes losses) (note 1/1.084 x 1.88 ~ 1.73...)
going to play with it some more using different parameters
480/1 in, 480/3 out, 200 HP motor load to 90%
starts under full load, ramps 1200 rpm/sec
took some time to detail the drive parameters, diode characteristics, snubber values, internal R, etc.
also to come up with the control system parameters, gains, etc., used speed control, but torque control can be configured also
bear in mind S is used, not P
S power in/out ~1.084, 8% losses
I in / I out ~ 1.88 (includes losses) (note 1/1.084 x 1.88 ~ 1.73...)
going to play with it some more using different parameters
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Not so. The caps are after the rectification so don't play a part in PFC.
The input power factor is a product of both displacment and distortion.
Displacement generally isn't a significant factor. The input stage is an uncontrolled rectifier.
Does PWM actually have a defined firing angle?
I don't see how but feel free to correct me.
Not so. Yes, the caps are after the rectification but they contribute significantly to output PFC. Without the caps, the output PF would be passed to the input.
He didn't say the output had a defined firing angle. Nevertheless, the firing angle does determine pulse width, does it not?
Not accurate, they supply reactive power, they impact line and load pf
they don't disappear, although i flow is not continuous, the C is apparent to the line
A contolled firing angle
I'm on my way out the door
I'll try to elaborate later
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Smart_$
I suggest a much simpler circuit consisting of a 1-ph, full-wave rectifier feeding a series R-L load (the motor) through a filter (the capacitor)!
I wlll provide detail if the moderator agrees the approach is not 'superfluous'!
Regards, Phil Corso
I suggest a much simpler circuit consisting of a 1-ph, full-wave rectifier feeding a series R-L load (the motor) through a filter (the capacitor)!
I wlll provide detail if the moderator agrees the approach is not 'superfluous'!
Regards, Phil Corso
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Whey back when DC loads were supplied with rectifiers connected to Xfmrs, "Utiiization-Factor" was used in place of Power-Factor, i.e., Pdc(out)/VA(in)
Phil Corso!
Not so. The input is an uncontrolled rectifier It's unidirectional*.
The required output fundamental frequency and voltage determine the switching pattern. The switching frequency is usually a parameter that can be selected within a given range.
We've designed for10kHz or more for high speed machine tool drives - upwards of 20,000 rpm.
*Yes, there are different configurations. I'm referring to the common or garden VFD which was the OP's take I believe.
If fed from a full wave rectifier it would have to be a DC motor. The op talke aabot a VFD output. That's not DC.
Given a VFD and a motor, a motor that powered without VFD exhibits a significant power factor, if that power factor disappears (becomes insignificant) when powered through the VFD, to what do you attribute the PFC?
I will give you credit for one thing, and that is, you sure know how to put a bunch of words together to mean absolutely nothing... and still make it sound important to the debate subject. Have you ever considered becoming a political speechwriter?
:blink:
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