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Three Phase 2 Level PFC inductor design

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chaitanyab

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Hi,

I am looking for an Appnote or reference for three phase 2 level boost PFC inductor design. The Basic 6 switch boost PFC. Surprisingly I am not able to find any reference on the internet. Any pointers will be appreciated.

Thanks
 

I don't see any reason why inductor design approach would be different for a three phase vs single phase boost PFC. Unless you want to do something strange like use a common core for the three inductors....
 

    chaitanyab

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3 triangle waves 120 deg apart ( say 20kHz ), a sine wave ref for each of the 3 phases, phase locked to the P-N voltage at input for each phase - some current limiting and decent gate drive and away you go -

an error amp running off the Vout ( DC ) to modulate the 3 sine wave refs above - and job done

- et Voila ... ! easy peasy ...
 

It's possible to have one common core for 3 inductors...
by staggering action at mutually exclusive times. My simulation turns on each switch at 20 percent duty cycle. It's enough time for 22mH to rise to 7 Amperes. At turn-Off the diodes conduct briefly, just before a neighboring coil turns On.

By 2 levels do you mean you want positive and negative outputs? If so then it requires a contrived gating scheme.

3-phase AC-fed boost converter clk-driv load 2kV.png
 

If you have 3 phase...you can just use a 6 pulse diode bridge.....and that gives you good enough PFC....as long as you keep the output cap of the bridge low enough.
 

Following Circuit is what I am looking for to design, especially the inductors:
1647264863425.png


Now as per mtwieg suggestion I have decided to use the single stage PFC inductor equations (which are abundantly available on internet / text book references)
Now normally three phase PFC is used for high power. In my case 10-20kw. 3 ph 415Vrms, 50Hz/60Hz input, probably give me 600VDC PFC output.
So I am thinking it will be CCM only. So in theory Single stage PFC design in CCM mode, use for 3 inductors should work is my understanding.

mtwieg and others please comment.
 

Even for just 6kW, a totem pole PFC which splits the single phase to 3 phases is used as in attached
...so it will be very demanding to do it with that cct in post #6.....what you show is , or appears to purport to be , a bridgeless 3 phase PFC......and i dont see the low frequency switch branch's for your phases.
I think #6 cct needs verification.
 

Even for just 6kW, a totem pole PFC which splits the single phase to 3 phases is used as in attached
...so it will be very demanding to do it with that cct in post #6.....what you show is , or appears to purport to be , a bridgeless 3 phase PFC......and i dont see the low frequency switch branch's for your phases.
I think #6 cct needs verification.
I think the circuit is correct, it does not need low frequency branch. It operates as described in post #3 ( three phase carrier locked to input voltage phase creating 3 phase PWM) unlike the totem pole which you have mentioned in the link which kind of operates with one phase and neutral and then all 3 put together.
 

I confirm that post #6 PFC circuit is industry standard, except for a missing LC filter that blocks PWM frequent currents. Also a DC bus precharge circuit in parallel to the mains contactor is required. I agree that the chokes can be basically analyzed as single phase chokes.

Similar to motor inverter, the PFC will use symmetrized modulation (superimposed 3*f0 zero sequence) to reduce the minimal DC bus voltage.
 

    chaitanyab

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