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3phase PI filter inductors and caps

Hi,

I am making a filter between a SMPS and a 3phase brushless DC generator, the SMPS draws pulses of current at 200kHz, with a peak draw of 12Amps. The rectified voltage of the brushless DC generator peaks at 385VDC. The SMPS rise/fall switching time is will about 20ns.

here is the schematic of the filter in ltspice:

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here are the current waveforms in each of the 3phases of the power source:

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I am wondering if this filtering is sufficient for a brushless DC generator or if the current ripple should be further reduced, also what would be the best way to reduce the current ripple? I have tried a 2 stage PI filter and played with the cap/inductor values but haven't been able to reduce the ripple much beyond that in the waveform above.

One possible inductor I am considering using for this filter is the HC1 Series: 3.6uH/13.4A saturation current

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The datasheet says it is designed for high current, low voltage. If I used this inductor for the high voltage PI filter would it still work, or is it possible that the windings would short out to the ferrite?

Another nice inductor (Also low voltage however):

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Reply to
Jamie Morken
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What's a 3-phase brushless DC generator? An alternator with output rectifiers? What is the description of sources V6-V8? Can you post the ascii file for the simulation? The datasheets for the inductors say "low voltage" without saying how low, so it probably wouldn't do to trust them.

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John
Reply to
John O'Flaherty

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Hi,

Yes it is just a 3phase alternator with 6 diodes. V6 to V8 are sinewave voltage sources offset by 120 degrees each to give three phase AC.

Here's the ascii text ltspice file:

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cheers, Jamie

Reply to
Jamie Morken

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I noticed about your first filter that it needs two more capacitors, from the bottom phase to the top, at least to be symmetrical for the three phases. Putting in series R & L in the alternator windings made the simulator break sometimes. I noticed that connecting a high (1e7 ohm) resistor from the common terminal of V6-V8 to ground fixed that. It occurred to me that putting a battery across the alternator output might smooth things out, and I tried to simulate that with a 1F capacitor (with 0.1 ohm ESR). It made the simulation very slow, so I don't know what the outcome would be. I also noticed that putting a 1 ohm resistor in series with this large capacitor broke the simulator (singular matrix error), but at that point I had to do other stuff.

Good luck.

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John
Reply to
John O'Flaherty

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