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digital PFC control ?

Discussion in 'Electronic Design' started by Adam Seychell, Aug 1, 2003.

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  1. It it feasible to implement active power factor correction using a low
    cost microcontroller to digitally control the voltage loop ?
    I have been reading information on the UC3854 PFC and it seemed that
    there are a number of problems with the analog approach of voltage
    outer loop control and these could be solved with simple DSP
    techniques. Since voltage loop bandwidths are low, the sample rates
    can be under 10 kHz. The PFC could be built from a conventional analog
    average current mode control boost converter, where the line current
    is programmed by the microcontroller/DAC. The micro would sample both
    the line voltage and output voltage. If such PFC control were possible
    then circuit complexity and cost would be less than the fully analog
    technique.
     
  2. James Meyer

    James Meyer Guest

    Except for the overhead needed for the A-D and D-A conversions.

    Jim
     
  3. Ashish

    Ashish Guest

    Hi!


    I am sorry for causing all that misconception about PFC converter
    control thru ASICs. The ASICs are just great and my UC3854 based unit
    is working just fine.

    No! you should not use a microcontroller for PFC control because
    1. Even though sampling the DC voltage at 100Hz( synchronized to
    zero-crossing of line voltage ) can give you great results. The uP are
    pretty slow and you will end up with a large inductor due to low
    switching frequency.
    2. uP based system are not that easy to design and the whole unit will
    be lot costlier that the unit build on ASIC.
    3. Since I have a system working I can help you with the design. It
    will not be that difficult.
     
  4. R.Legg

    R.Legg Guest

    The micro would sample both
    A mico is cheaper than an analog multiplier?

    Count the transistors. Estimate the silicon real estate. Recalculate.

    http://ece-www.colorado.edu/~pwrelect/pubarch/fast-pfc-apec02.pdf

    RL
     
  5. There's almost no market for analog multipliers, so the price is
    astronomical.

    * The B-B/TI MPY634 is $15+ in 100's.

    * A PIC12F675 with 10-bit ADC is $1.26.

    Of course the MPY634 can work at 10MHz. ;-)

    Don't know if the old MC1495 is still made, I see a price of about $8
    in 100's, but not from a real distributor.

    Best regards,
    Spehro Pefhany
     
  6. legg

    legg Guest

    How much is the multiplier inside a UC3854?

    I don't think we're talking about small-scale integration here. We're
    talking at least about an ASIC or PLD.

    Then we're talking about package size and minimum pin count for the
    same volume of product.

    RL
     
  7. Good point, the chip is about the same price as the PIC, & there are
    also inexpensive and accurate analog multipliers inside some energy
    metering ASICs, IIRC.

    Best regards,
    Spehro Pefhany
     
  8. We did it at my place of work. Saved a lot of circuits. The key is to keep
    the inner loop current mode and analog, then there's no problem doing the
    multiplying and the other stuff in the micro

    Cheers

    Klaus
     
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