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PWM feedback

Discussion in 'Electronic Design' started by [email protected], Dec 18, 2013.

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  1. Guest

    This is more of a practical question. I understand feedback and how it works and can design controllers. However, these have been for dc (non PWM) motors using tachos with a dc output.

    What I want to know is how you achieve this with digital tachos which give out pulses.

    I am thinking that the set point is still dc as before (or software based) and you just count the pulses from the tacho in a given time and this gives an error signal which you then generate PWM from - am I right? the rest is usual lag-lead compensators etc.

    Another approach I suppose would be to have a square wave as the set-point and use the pulses from the tacho and create a phase-detector and PLL approach.
  2. Den onsdag den 18. december 2013 21.42.31 UTC+1 skrev :
    unless you have a huge number of lines I'd measure the period of the pulses
    measuring the period of the pulses and comparing to what you want the period
    to be is sorta the same

  3. dp

    dp Guest

    Usually instead of measuring frequency (counting pulses in a window)
    measuring period (counting clock pulses with the sensor pulses being
    the window) solves this issue if existing, one just uses a fast enough

  4. Guest

    Low pass filtering = phase lag and less phase margin. So it will have to be outside the closing unity gain frequency I assume.
  5. Guest

    Yes but you are going to have to filter it hard to get dc out of PWM. Won't you just get a sine wave with a weak filter.
  6. josephkk

    josephkk Guest

    Back in the day ('bout 40 years ago) there were some really good frequency
    to voltage converter ICs. The principles are still valid. Most digital
    versions are translations of the method, pretty similar to count them up
    over some fixed repeating period.

  7. And they still exist in many venders!

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