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How to control AC frequency?

Discussion in 'General Electronics Discussion' started by hopperms, Mar 17, 2013.

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  1. hopperms

    hopperms

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    Jan 22, 2013
    I am trying to use AC current to power multiple electromagnets but here's the catch: I need them to be in different points in the phase (so one at 0˚, 90˚, 180˚, 270˚, 0˚, etc.). I was thinking that maybe I could use inverters started at different times but I don't know if that would even work. Preferably, I would also like to be able to change the frequency as well. Does anyone have any idea as to how I could approach this?

    Any help is appreciated.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Use a microcontroller to generate digital signals with the right fundamental frequency and phase.
    If your signals need to be sinusoidal (i.e. you cannot accept a digital signal), use low pass filters at the output of the micocontroller to remove the higher harmonics. Note, however, that the low pass filters will vary your output signal when you change the frequency.

    You could use a digital to analog converter for each channel to approximatge a sine wave. As far as I understand what you are trying to do this may be overkill.

    Or Google 3 phase motor control.
     
  3. hopperms

    hopperms

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    Jan 22, 2013
    I'm not sure if the microcontroller method would work due to a larger power supply needed, and the ADC method wouldn't work for the same reason.

    However, after looking up 3 phase motor control, I think that will work.

    Thanks!
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    2,656
    Nov 17, 2011

    Of course you will have to add suitable driver circuits to control the power. Either simple transistor switches (for the digital method) or true amplifiers (for the DAC method).
     
  5. Electrobrains

    Electrobrains

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    Jan 2, 2012
    What are the ratings (voltage, current) of the solenoids?
    What voltage do you intend to use as supply?
    What frequency range would you like?
     
  6. hopperms

    hopperms

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    Jan 22, 2013
    My mistake. I later realized what you meant. After thinking about it for a while, I think the 3 phase motor method just won't be feasible, especially within my budget. Instead, I am planning on using the microcontroller method, using the schematics here: http://www.instructables.com/files/deriv/FKP/V8N5/H6I6WJTO/FKPV8N5H6I6WJTO.LARGE.jpg to get the positive and negative voltages sharing a common ground.

    As for the voltage and current I will be using, I'm not sure of the exact values yet but I plan on using 12V with maybe as high as 10A (using copper tape instead of the thin wire).
     
  7. Electrobrains

    Electrobrains

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    5
    Jan 2, 2012
    Do you need sine wave output or can you supply your solenoids with square wave (makes it much easier)?
    Do you need 4 phases?
     
  8. hopperms

    hopperms

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    Jan 22, 2013
    I think I can make due with the square waves. As for the phases, I'm not sure how many I will need but I have a pretty good idea of how to design/program multiple phases. I think I've got it from here.

    Thanks everyone!
     
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