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Fourier series in Multisim

  1. Sep 18, 2014 #1

    etf

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    Is it possible to represent some signal in terms of Fourier series in Multisim? For example, Fourier series of sawtooth voltage with period T=2pi is $$\sum_{n=1}^{\infty }\frac{2}{n}(-1)^{n+1}sin{(nt)}=2sin{(t)}-sin{(2t)}+\frac{2}{3}sin{(3t)}-\frac{1}{2}sin{(4t)}+...$$. These terms on right side of equation will be AC voltage sources connected in series. For good approximation of sawtooth waveform I should use few hundreds terms of series. It would be impossible to connect all these sources manually :) Is there any better way to do this?
     
    Last edited: Sep 18, 2014
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  3. Sep 18, 2014 #2

    Baluncore

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    It would be easier to simulate a circuit that generates a linear sawtooth than to correctly phase and sum all those fourier terms.
     
  4. Sep 18, 2014 #3

    etf

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    I know there is sawtooth generator in Multisim but I used sawtooth waveform only as example. I was wondering is it possible to simulate random periodic signal which can be represented through Fourier series.
     
  5. Sep 18, 2014 #4

    Baluncore

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    How many different frequencies can Multisim generate at one time? One, or more?
    How would you synchronise the phases to get the correct time domain signal?
     
  6. Sep 20, 2014 #5

    etf

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    I'm not sure I can give you right answer. If it's impossible in Multisim, can it be done in Simulink maybe? Here is my program in Matlab to plot Fourier series of sawtooth waveform:

    clear
    clc
    t=linspace(0,2*pi,1000);
    suma=0;
    for n=1:10000
    suma=suma+((2./n).*(-1).^(n+1)).*sin(n.*t);
    end
    plot(t,suma)
    grid

    Can I link it somehow with Simulink to generate this waveform?
     
  7. Sep 22, 2014 #6

    etf

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    Finally I solved it!
    In order to simulate arbitrary periodic signal written in terms of Fourier series, it is necessary to calculate sum using my code for example, post #5 (Bigger n - better approximation.) . For every value of t we have appropriate value of "suma". Then we have to save our data in text file, time goes in first column and values for "suma" goes in second column. Then we load our text file in PWL Voltage in Multisim (Enter data points int table - Initialize from file...) and that's it
     
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