Re: 3phase PFC



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%20PFC/series%20boost%20inductors.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%20PFC/series%20boost%20inductors%20dual%20switches.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%20PFC/series%20boost%20inductors%20with%20short.jpg";

cheers,
Jamie


MooseFET wrote:
On May 7, 10:56 pm, Jamie Morken <jmor...@xxxxxxx> wrote:
Hi,

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

"http://www.rocketresearch.org/new/3phase%20PFC/3-phase%20vienna%20rec...";

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%20PFC/3phase%20PFC%20using%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%20PFC/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.


cheers,
Jamie

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