3phase PFC

[Jamie Morken]

Hi,

I'm trying to make a 3phase PFC circuit based on this schematic:

"http://www.rocketresearch.org/new/3phase PFC/3-phase vienna rectifier.jpg"

more info about this circuit:

"http://www.rocketresearch.org/new/3phase PFC/3phase PFC using vienna rectifier.doc"


I'm doing a test in ltspice with this circuit and three single phase PFC
controller IC's (ie. LT1249) but am not sure how to wire up these IC's
to detect the input phases bipolar voltages and currents, as for single
phase the input voltages and currents are just positive.

Here is the ltspice circuit so far:

"http://www.rocketresearch.org/new/3phase PFC/3phase ltspice test.zip"

Are there any 3phase PFC controller IC's out there?

cheers,
Jamie

 

[MooseFET]

Hi,

I'm trying to make a 3phase PFC circuit based on this schematic:

"http://www.rocketresearch.org/new/3phase PFC/3-phase vienna rec..."

Circuits with the word "fuzzy" in them rarely work as well as ones
without it.

more info about this circuit:

"http://www.rocketresearch.org/new/3phase PFC/3phase PFC using%2..."

I'm doing a test in ltspice with this circuit and three single phase PFC
controller IC's (ie. LT1249) but am not sure how to wire up these IC's
to detect the input phases bipolar voltages and currents, as for single
phase the input voltages and currents are just positive.

Here is the ltspice circuit so far:

"http://www.rocketresearch.org/new/3phase PFC/3phaseltspice test.zip"

Are there any 3phase PFC controller IC's out there?

IR may have one.


This may be a case where "use a PIC" really is the right answer. In a
converter of this size, the cost of a slightly more complex controller
section may be worth it. If you have a part that can remember what
happened a full cycle ago, you can do a much better job on bringing
the out of phase and harmonic content down to zero.

 

[Jamie Morken]

Circuits with the word "fuzzy" in them rarely work as well as ones
without it.


IR may have one.


This may be a case where "use a PIC" really is the right answer. In a
converter of this size, the cost of a slightly more complex controller
section may be worth it. If you have a part that can remember what
happened a full cycle ago, you can do a much better job on bringing
the out of phase and harmonic content down to zero.

Hi,

My three phase source (a brushless generator) has a wide output voltage
range, rectified from 60VDC all the way up to 360VDC depending on the
RPM, the power output scales fairly linearly over this range, from only
60watts at 60VDC, all the way up to about 1300watts at 360VDC.

I would like the output of the 3phase PFC boost to be about 400VDC or so
over the whole input voltage range. Is it possible to maintain a high
efficiency (96%+ ideally) over this whole range using the same boost
inductors, or would it be better to switch boost inductors depending on
the input voltage.


I am trying to size the PFC boost inductors for this using this tool:

http://www.daycounter.com/Calculators/Switching-Converter-Calculator.phtml

For the same output voltages, it suggests a high inductance inductor at
the low voltage input, low power output, and then a smaller inductance
inductor at higher input voltage, higher power output.

I'm not sure how to size this inductor for the whole voltage range.

cheers,
Jamie

 

[Tony]

If you're trying to convert a dedicated source like a car alternator that already has a
rectifier, why go to the trouble of a 3 phase PFC? In fact, why worry about PFC at all? A
simple single step-up converter should be fine for those power levels (with
current-controlled inner loop and slower outer voltage loop).

 

[Jamie Morken]

If you're trying to convert a dedicated source like a car alternator that already has a
rectifier, why go to the trouble of a 3 phase PFC? In fact, why worry about PFC at all? A
simple single step-up converter should be fine for those power levels (with
current-controlled inner loop and slower outer voltage loop).

Hi,

It is more efficient to use a PFC stage rather than a boost stage as the
generators RMS current is lower with PFC. This means more energy can be
extracted from the generator for the same work input and the heat in the
generator will be lower for the same output power level.

cheers,
Jamie

 

[Jamie Morken]

Hi,

Since only small output current is required at low input voltages,
but this requires a large inductance, and then large output current
is required at higher input voltages, which requires a smaller
inductance, can these two inductors be put in series, and the high
inductance one will saturate when the input voltage is high, or would
it require a bypass current path (ie. relay) to short out this inductor?

Here's a boost circuit with what I am thinking of:

"http://www.rocketresearch.org/new/3phase PFC/series boost inductors.jpg"

If the second inductor doesn't saturate then the inductance will be too
large for high input voltages, so maybe the switching frequency could
be decreased.

Here's another circuit I was thinking of, it uses two switches, S2 runs
at low input voltages to get the large inductance, and then S1 runs at
higher input voltages with only the 300uH inductor.

"http://www.rocketresearch.org/new/3phase PFC/series boost inductors dual switches.jpg"

Here's one more using two mosfets to short out the large inductor for
decreasing the inductance at high input voltages:

"http://www.rocketresearch.org/new/3phase PFC/series boost inductors with short.jpg"

cheers,
Jamie

 

[legg]

Hi,

It is more efficient to use a PFC stage rather than a boost stage as the
generators RMS current is lower with PFC. This means more energy can be
extracted from the generator for the same work input and the heat in the
generator will be lower for the same output power level.

You might want to crunch some numbers on this for the 3ph case, while
examining other methods of power factor correction that are available.

What you should really be considering is deliverable power vs your
requirement and permissible temperature rise.

PFC requirements are primarily driven by legislation based on
infrastructure requirements, not by end-use economics or concerns
about efficiency, as such. Your source is free from that major
influence.

RL

 

[legg]

Since only small output current is required at low input voltages,
but this requires a large inductance, and then large output current
is required at higher input voltages, which requires a smaller
inductance, can these two inductors be put in series, and the high
inductance one will saturate when the input voltage is high, or would
it require a bypass current path (ie. relay) to short out this inductor?

This is intuitively backwards from your real application requirement.
For a constant power drain, current will increase as voltage reduces.
This argues for an inductor that handles higher current at low voltage
input, while still having an inductance that is still high enough to
be practically functional (not discontinuous) at higher input
voltages.

For the same power transfer, the low voltage inductor would have a
lower inductance, if you were actually switching between optimum part
types. The optimum parts have energy storage requirements that
increase at lower input, but this energy storage is related to the
square the current.

If you are considering altering RPM to adjust for power drain
(suggested by your lower current lower voltage reference), you might
just as well do so to crudely regulate the generator output voltage
instead, considerably reducing the work of downstream regulators.

RL

 

[MooseFET]

Hi,

My three phase source (a brushless generator) has a wide output voltage
range, rectified from 60VDC all the way up to 360VDC depending on the
RPM, the power output scales fairly linearly over this range, from only
60watts at 60VDC, all the way up to about 1300watts at 360VDC.

Being able to work over that range pushes the cost of the inductors up
a lot. It seems to me that you really don't need a good PFC so much
as a good booster design.

I would like the output of the 3phase PFC boost to be about 400VDC or so
over the whole input voltage range. Is it possible to maintain a high
efficiency (96%+ ideally) over this whole range using the same boost
inductors, or would it be better to switch boost inductors depending on
the input voltage.

You may be better off with a two range design. With low input
voltages you are beyond where the simple booster works well and into
where a transformer looks better. Perhaps you could share the
inductive elements. I'm thinking of something like this:


========================
-----))))))----+-----))))))-----+------>!--- To load
! !
!!- V
----!! Q1 --- D1
!!- !
! !!-
GND ---!! Q2
!!-
!
GND

Q1 is only used when the voltage is low. At high voltages Q2 is
used. D1
is needed to keep reverse current out of Q2 when Q1 is on.

 

[MooseFET]

Hi,

My three phase source (a brushless generator) has a wide output voltage
range, rectified from 60VDC all the way up to 360VDC depending on the
RPM, the power output scales fairly linearly over this range, from only
60watts at 60VDC, all the way up to about 1300watts at 360VDC.

I would like the output of the 3phase PFC boost to be about 400VDC or so
over the whole input voltage range. Is it possible to maintain a high
efficiency (96%+ ideally) over this whole range using the same boost
inductors, or would it be better to switch boost inductors depending on
the input voltage.

I am trying to size the PFC boost inductors for this using this tool:

http://www.daycounter.com/Calculators/Switching-Converter-Calculator....

For the same output voltages, it suggests a high inductance inductor at
the low voltage input, low power output, and then a smaller inductance
inductor at higher input voltage, higher power output.

Try changing the frequency with the input voltage. This reduces the
range of the inductors.

 

[legg]

- All the controller outputs were labeled for ph1 - effectively
shorted together

- All modulator references had the same phase angle. (After
correction, your model will not work with alt solver, so you'll have
to switch back to the normal solver.)

- There was no current feedback. This chip expects to see
negative-going current sensing signals on the Mout pin of less than
1V1 peak.

- Once running, you have to load it to get current waveforms.

- Don't expect to see attempted regulation prior to the 6.5mSec
timestamp, as the inrush and overshoot doesn't clear prior to that
time, even with a 1KW load. Also don't expect 60Hz performance at
600Hz.

The asc file is reworked (and still needs much more attention to run
properly as a simulation) at:

http://www.magma.ca/~legg/TVS/1249-3phase-2.zip

With simulations that take as long to run as this one does,
doublechecking your work, your ideas and your aims becomes important,
prior to pressing the GUI's 'run' button. Make sure you've got plenty
of drive space. The raw files mount up at the rate of about 150Meg per
millisecond of active converter runtime.I'm always surprised that they
run at all.

The Vienna rectifier is about the most expensive,complicated and lossy
version of PFC correction that a body could have picked.

RL

 

[Jamie Morken]

- All the controller outputs were labeled for ph1 - effectively
shorted together

- All modulator references had the same phase angle. (After
correction, your model will not work with alt solver, so you'll have
to switch back to the normal solver.)

- There was no current feedback. This chip expects to see
negative-going current sensing signals on the Mout pin of less than
1V1 peak.

- Once running, you have to load it to get current waveforms.

- Don't expect to see attempted regulation prior to the 6.5mSec
timestamp, as the inrush and overshoot doesn't clear prior to that
time, even with a 1KW load. Also don't expect 60Hz performance at
600Hz.

The asc file is reworked (and still needs much more attention to run
properly as a simulation) at:

http://www.magma.ca/~legg/TVS/1249-3phase-2.zip

With simulations that take as long to run as this one does,
doublechecking your work, your ideas and your aims becomes important,
prior to pressing the GUI's 'run' button. Make sure you've got plenty
of drive space. The raw files mount up at the rate of about 150Meg per
millisecond of active converter runtime.I'm always surprised that they
run at all.

The Vienna rectifier is about the most expensive,complicated and lossy
version of PFC correction that a body could have picked.

Thank you for modifying the sim to work!

What circuits would be better than the vienna rectifier for 3phase
PFC? I found two other ones:

http://www.rocketresearch.org/new/3phase PFC/3 phase PFC stage.png
http://www.rocketresearch.org/new/3phase PFC/3 phase PFC stage2.jpg

I would like to generate +220V and -220V rails, and use them to generate
splitphase 120VAC sine waves using halfbridges and two LC filters. What
would be the best 3phase PFC circuit to generate these two rails, or if
not using 3phase PFC, could a boost circuit off the 3phase 6diode
rectifier generate a positive and negative rail?

cheers,
Jamie

 

[Jamie Morken]

Being able to work over that range pushes the cost of the inductors up
a lot. It seems to me that you really don't need a good PFC so much
as a good booster design.



You may be better off with a two range design. With low input
voltages you are beyond where the simple booster works well and into
where a transformer looks better. Perhaps you could share the
inductive elements. I'm thinking of something like this:


========================
-----))))))----+-----))))))-----+------>!--- To load
! !
!!- V
----!! Q1 --- D1
!!- !
! !!-
GND ---!! Q2
!!-
!
GND

Q1 is only used when the voltage is low. At high voltages Q2 is
used. D1
is needed to keep reverse current out of Q2 when Q1 is on.

Hi,

Can the inductors also be on separate cores? For a 60VDC to 380VDC
input voltage range, with linear power increase with voltage up to
2kW at 380VDC, and 60watts at 60VDC input, what inductances would be
a good starting point for these two inductors?

cheers,
Jamie

 

[Jamie Morken]

Try changing the frequency with the input voltage. This reduces the
range of the inductors.

I'm using an FPGA, so can control the PWM frequency (increase it for
lower input voltage), With this method and the linear graph of input
voltage over output power (required output power is low with low input
voltage) would it be possible to use a single stage boost design and
still have high efficiency over the whole range? Or is it a good idea
to use the two stage boost as well as variable frequency? Easy to do
in an FPGA, so the only real variable is finding good inductances to use
I think!

cheers,
Jamie

 

[JosephKK]

You might want to crunch some numbers on this for the 3ph case, while
examining other methods of power factor correction that are available.

What you should really be considering is deliverable power vs your
requirement and permissible temperature rise.

PFC requirements are primarily driven by legislation based on
infrastructure requirements, not by end-use economics or concerns
about efficiency, as such. Your source is free from that major
influence.

RL

Yes and no. Energy efficiency improvements do have economic payback.

 

[Jamie Morken]

Being able to work over that range pushes the cost of the inductors up
a lot. It seems to me that you really don't need a good PFC so much
as a good booster design.



You may be better off with a two range design. With low input
voltages you are beyond where the simple booster works well and into
where a transformer looks better. Perhaps you could share the
inductive elements. I'm thinking of something like this:


========================
-----))))))----+-----))))))-----+------>!--- To load
! !
!!- V
----!! Q1 --- D1
!!- !
! !!-
GND ---!! Q2
!!-
!
GND

Q1 is only used when the voltage is low. At high voltages Q2 is
used. D1
is needed to keep reverse current out of Q2 when Q1 is on.

I guess this is like an autotransformer?

cheers,
Jamie

 

[legg]

Yes and no. Energy efficiency improvements do have economic payback.

Depends on whether you're designing hardware to cook for ten thousand,
or just two.... Or maybe even just planning a menu.

RL

 

[MooseFET]

I guess this is like an autotransformer?

Yes that is the winding polarity I was suggesting. You still need a
physically larger inductor to be able to do it.

Not combining the inductors may be better from the point of view of
needing two smaller cores in place of one large one.

 

[Jamie Morken]

LOL. too true. Im sure they could have added a few more diodes if they
had tried just a little bit harder

Thank you for modifying the sim to work!

What circuits would be better than the vienna rectifier for 3phase
PFC? I found two other ones:

http://www.rocketresearch.org/new/3phase PFC/3 phase PFC stage.png

http://www.rocketresearch.org/new/3phase PFC/3 phase PFC stage2.jpg


I would like to generate +220V and -220V rails, and use them to generate
splitphase 120VAC sine waves using halfbridges and two LC filters. What
would be the best 3phase PFC circuit to generate these two rails, or if
not using 3phase PFC, could a boost circuit off the 3phase 6diode
rectifier generate a positive and negative rail?

cheers,
Jamie

It sure can. use a pair of boost converters, with a half-bridge as the
switches, the center-tap of which becomes 0V. So its:


---nnnnnn---+--->|-----+--- V+
| |
3ph X [Cbig]
BR | |
+--0V------+
| |
X [Cbig]
| |
---nnnnnn---+---|<-----+--- V-


X is typically an IGBT half-bridge, but can be FETs etc.

Hi Terry,

Thanks for the dual rail boost!

the same trick used to make a single-phase boost PFC (force current to
follow envelope of full-wave rectified line voltage) also works for
three-phase systems; the 6-diode bridge automagically "unfolds" the
current waveform.

Is this an alternate circuit to the vienna rectifier for 3phase PFC?
Do you have a schematic of it?

Here's an ltspice sim from Larry Carroll on the ltspice yahoo
group, it implements 3phase PFC with one cycle PFC control!

"http://www.rocketresearch.org/new/3phase PFC/lbcarroll backup.zip"

cheers,
Jamie

 

[MooseFET]

MooseFET wrote: [....]
I'm using an FPGA, so can control the PWM frequency (increase it for
lower input voltage), With this method and the linear graph of input
voltage over output power (required output power is low with low input
voltage) would it be possible to use a single stage boost design and
still have high efficiency over the whole range?

You can get a wide range and good efficiency but you end up with a
mechanically large inductor and switch device.

Or is it a good idea
to use the two stage boost as well as variable frequency?

Each stage should be limited to about a 4:1 voltage range.