Power electronics principle

Discussion in 'Homework Help' started by Peijie Xu, Aug 18, 2015.

  1. Peijie Xu

    Thread Starter New Member

    Aug 18, 2015
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    Hi guys,
    i am confusing about the mean value of |i| in this case.
    Fs = 3.8kHz, Duty cycle(D) = 0.73, delta i = 4.9A
    If the above waveform is VL, how to get the mean value of |i|?
    I found Ton maybe equal 0.73*1/3800.
    According to VL= L * di / dt, i got L? Untitled.png
     
  2. DickCappels

    Moderator

    Aug 21, 2008
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    The term "mean" can be replaced with the term "average". Does that help?
     
  3. Peijie Xu

    Thread Starter New Member

    Aug 18, 2015
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    Sry Cappels , i mean i dont know how to calculate it, cheers.
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    But do you understand what an "average" is?
     
  5. MrAl

    Well-Known Member

    Jun 17, 2014
    2,418
    488
    Hi,

    Are you tying to get the mean (or average) current through an inductor?

    To get the average you usually integrate, but it may be simpler in some cases.
    Did you ever do this before? For example, can you find the average of VL itself?
     
  6. Peijie Xu

    Thread Starter New Member

    Aug 18, 2015
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    I understand the average, I try to sketching the figure of I...
     
  7. Peijie Xu

    Thread Starter New Member

    Aug 18, 2015
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    0
    No...I never did before. I think calculating VL need L*di/dt. Is it right?
     
  8. MrAl

    Well-Known Member

    Jun 17, 2014
    2,418
    488
    Hi,

    Then maybe you should concentrate on calculating the average of VL first since you have been given that information already. Once you master that, you can move on to calculating the average of the current which is what i think you are after.

    Do you know how to integrate?
     
  9. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    Since this is a repetitive waveform, you have to take into account that you don't know the initial state (unless you can determine it based on symmetry). But since you pretty much have to assume that the system is operating in AC steady state, you know that the state at the end of a complete cycle is the same as at the beginning of that cycle.

    You haven't given much of a clue regarding what the circuit is that this applies to. Is the sketched waveform the voltage applied to an inductor?

    Sketch what the current in the inductor looks like. For starters, go ahead and assume that the current starts at zero.

    Once you have that sketch, take the absolute value of it.

    Then find the average value of that.

    Show your work as far as you can.
     
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