How to Plot FFT for Matlab?

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Matthew Jacobs
Matthew Jacobs 2018-11-14
回答： Star Strider 2018-11-14
I'm kind of confused on what exaclty I'm expected to plot as the frequency domain kinda confuses me.
I'm given Vout from the circuit in Simulink:
Screen Shot 2018-11-13 at 9.07.28 PM.png
From there I'm told to:
  • Parametrize the provided Simulink model
  • Extract Vout to workspace
  • Include a section in your script to find the peak value of the fundamental of Vout (Fourier decomposition)
  • Find Vout/ (Vin/2)
  • Use a "for" loop to create at least 10 points for the final plot (5 values of ma < 1 and 5 > 1). Make sure saturation is visible.
My problem is with the 3rd step in the bullitin. How do I find the fundamental? My professor gave a hint of using fft in matlab on Vout. I tried max(fft(Vout)) and got the result
=-4.0000e+01 + 2.5465e+07i But I don't think is is right as there is an imaginary value but I need it as a voltage. Any help would be great. Thanks!

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回答（1 个）

Star Strider
Star Strider 2018-11-14
The result of the Fourier transform will be complex. Use the abs() (absolute value) function to recover the amplitude from the complex quantities.

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