Help needed for Fourier analysis of a triangular wave

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Discussion Overview

The discussion revolves around the Fourier analysis of a triangular wave, specifically in the context of a boost converter. Participants explore various approaches to modeling the wave function and seek alternative solutions for comparison.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation
  • Debate/contested

Main Points Raised

  • The original function for Fourier analysis is presented with specific equations for different intervals of time, with a focus on the duty cycle and amplitude.
  • One participant suggests a different approach using the interval [-π,π] and identifies the function as an odd function, leading to a more compact series representation.
  • Another participant expresses the need to model the equation using MATLAB or Maple, indicating a desire for practical application of the theoretical work.
  • A concern is raised about the symmetry of the output waveform compared to the original waveform, suggesting the need for a DC component to achieve the desired shape, while noting the lack of proof for this assertion.
  • One participant points out potential mistakes in the intervals of the original function as expressed in a spreadsheet and provides a plot comparing the original function with their derived series, indicating they appear similar under certain conditions.

Areas of Agreement / Disagreement

Participants express differing views on the symmetry of the waveform and the necessity of a DC component. There is no consensus on the correctness of the original function or the proposed modifications, and the discussion remains unresolved.

Contextual Notes

Participants note potential mistakes in the original function's intervals and the dependence of the peak amplitude on other parameters, which may affect the analysis.

sabrank
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Homework Statement



Fourie analysis for a boost converter
Where d = duty cycle, A = amplitude and t = time

Homework Equations




Fx = (2At/d) for 0<t<d/2, -A+(2A/(1-d))*(1-t-d/2) for d/2<t<(1-d/2); (2A/d)*(t-1) for 1-d/2 <t<1.
Where d = duty cycle, A = amplitude and t = time

The Attempt at a Solution



My solution is kind off large, I need need another solution to compare my ans with before writing a script to execute this function.
 
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I recast your problem slightly and got a pretty compact answer. Instead of working with the interval [0,1], I used the interval [-π,π], took advantage of the fact it is an odd function, and got

[tex]f(x) = \sum_{n=1}^\infty \frac{2A\sin{n\pi d}}{d(1-d)n^2\pi^2}\sin nt[/tex]

Your d might be my 1-d and vice versa, and you can rescale t by a factor of 2π to get back to your original function.
 
Thank you Vela, currently trying to model the equation in MATLAB or maple 13, hopefully I will. Cheers
 
Please find attached the wave form I am trying to analyze. I was actually able to simulate the equation given by Vela but the output was symmetrical around zero while my original wave form as shown in the attachment was not symmetrical around zero.
I feel there should be a dc component in order to achieve this waveform consequently an odd function might not be assumed. Please note I have no proof of this.

A is the peak amplitude and 2A could be taken as peak to peak value (A-(-A)), which is equal to 3 in the attached waveform though I will prefer non usage of real value for 'A' because the value of 'A' changes with a change in other parameters e.g. d.

I will appreciate all assistance and suggestion. Thank you
 

Attachments

Last edited:
I'm assuming the function you gave in your original post is the correct one as the one expressed on the spreadsheet has apparent mistakes in the intervals for t.

I've attached a plot of your original function and the series I found (10 terms and with t appropriately rescaled). I used A=1 and d=1/4 for this particular plot. They look the same to me.
 

Attachments

  • fourier.jpg
    fourier.jpg
    7.2 KB · Views: 423

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