Representing Signals with Fourier Series in Multisim

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Discussion Overview

The discussion revolves around the representation of signals using Fourier series in Multisim, particularly focusing on the challenges and methods for simulating complex waveforms, such as sawtooth and other periodic signals. Participants explore both theoretical and practical aspects of signal generation and simulation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the feasibility of representing a sawtooth signal in Multisim using Fourier series, noting the complexity of connecting numerous AC voltage sources for accurate approximation.
  • Another participant suggests that simulating a circuit to generate a linear sawtooth may be easier than summing Fourier terms accurately.
  • A different participant raises the possibility of simulating random periodic signals that can be represented by Fourier series, beyond just the sawtooth waveform.
  • Questions are posed regarding the number of frequencies Multisim can generate simultaneously and the methods for synchronizing phases to achieve the correct time domain signal.
  • One participant expresses uncertainty about the capabilities of Multisim and inquires whether similar tasks could be accomplished in Simulink, sharing a MATLAB program for plotting Fourier series of a sawtooth waveform.
  • A later reply describes a solution involving the calculation of Fourier series sums using MATLAB, saving the results to a text file, and importing this data into Multisim to simulate arbitrary periodic signals.

Areas of Agreement / Disagreement

Participants express differing views on the capabilities of Multisim for simulating Fourier series representations, with some suggesting alternative methods or software like Simulink. The discussion remains unresolved regarding the best approach for generating complex waveforms in Multisim.

Contextual Notes

Limitations include the potential complexity of manually connecting numerous sources for accurate signal representation and the dependence on specific software capabilities for signal generation and synchronization.

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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?
 
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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.
 
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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.
 
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?
 
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?
 
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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