Representing Signals with Fourier Series in Multisim

In summary, the conversation discusses the possibility of representing a signal in Multisim using Fourier series, specifically using a sawtooth waveform as an example. It is mentioned that it would be difficult to manually connect all the AC voltage sources needed to simulate the waveform accurately and the question is raised about how many frequencies Multisim can generate at once and how to synchronize the phases. The possibility of using Simulink instead is also brought up. The conversation ends with the solution of using a Matlab program to plot the Fourier series and then transferring the data to Multisim using a text file.
  • #1
etf
179
2
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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  • #2
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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  • #3
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.
 
  • #4
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?
 
  • #5
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?
 
  • #6
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
 

1. What is a Fourier series in Multisim?

A Fourier series is a method for representing a periodic signal as a sum of simple sine and cosine waves. In Multisim, it is a tool used to analyze and manipulate signals in the frequency domain.

2. How do I access the Fourier series tool in Multisim?

The Fourier series tool can be accessed by clicking on the "Analysis" tab in Multisim and selecting "Fourier Analysis" from the drop-down menu.

3. Can I use Fourier series in Multisim for non-periodic signals?

No, Fourier series in Multisim is specifically designed for analyzing periodic signals. For non-periodic signals, other tools such as Fourier transforms may be more appropriate.

4. Can I customize the parameters of the Fourier series in Multisim?

Yes, Multisim allows users to adjust the frequency, amplitude, and phase of each component wave in the series. Users can also choose the number of terms to include in the series.

5. How does Multisim calculate the Fourier series?

Multisim uses the Fast Fourier Transform (FFT) algorithm to calculate the Fourier series. This algorithm is efficient and can quickly compute the frequency components of a signal.

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