RLC circuit

  1. May 27, 2011 #1
    Hi...i have question on RLC circuit. Why my max.voltage of complex sinewave in Excel is different from the simulated complex waveform? which one is right?

    max.voltage of complex waveform in excel = 106.8V

    max.voltage of complex waveform in simulation = 126.8V

    Should it be the same?
     
  2. jcsd
  3. May 27, 2011 #2
    Can you provide more details about the circuit so we can do analysis and compare?
     
  4. May 28, 2011 #3
    v = 110sinωt + 22sin(3ωt + 50⁰) + 5.5sin(5ωt - 35⁰)

    R = 25 , L = 100mH , C = 11.3uF .....in RLC series circuit

    Freq = 50Hz


    that are the details of the circuit....
     
  5. May 28, 2011 #4

    gneill

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    Staff: Mentor

    Which voltage are you concerned with? The voltage that is the sum of the supply voltages (your v above), or a voltage measured across one or more of the circuit components? If the latter, which component(s)?
     
  6. May 28, 2011 #5
    the voltage im concerned with is the output voltage (the last voltage coming out through all the components)....with all the voltages connected (in series) in one circuit.
     
  7. May 28, 2011 #6

    gneill

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    Staff: Mentor

    Hmm. I'm afraid that doesn't make things clear to me. What is the last voltage coming out of a series circuit? Where's the end of a circle?

    I've attached a figure of the circuit diagram for a series RLC circuit driving by three voltage sources. I've placed labels a,b,c,d at various points in the circuit path. Suppose we can measure the voltage between any chosen pair of labels (ab, ac, ad, bc, bd,...). Which pair represents the voltage that you're interested in?
     

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  8. May 28, 2011 #7
    the voltage im after is at 'a'...the voltage coming out from the capacitor which is the output voltage waveform
     
  9. May 28, 2011 #8

    gneill

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    Between a and what other point? Voltage is a potential difference. What's the reference point?
     
  10. May 29, 2011 #9
    it is the voltage at a and d....
     
  11. May 29, 2011 #10

    gneill

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    Staff: Mentor

    Okay. So the voltage you want is directly across the summed voltage supplies. This means that the other circuit components are irrelevant to the issue because the voltage supplies alone dictate their own voltages (assuming ideal voltage supplies).

    The problem then boils down to finding the maximum absolute value for the function

    f(θ) = 110 sin(θ) + 22 sin(3θ + 50°) + 5.5 sin(5θ - 35°)

    Note that the function is periodic since it's the sum of periodic terms. The "fundamental" period corresponds to is 2π radians for θ -- all the terms of the function complete an integer number of complete cycles over that domain. If you plot the function over this domain you will observe the peaks (see figure attached).

    To find the actual values of the peaks, use whatever mathematical tools you are familiar with for finding function maxima and minima.
     

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