Simulink to see Fourier

Question

Robert Scott 2024-4-20

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https://ww2.mathworks.cn/matlabcentral/answers/2109506-simulink-to-see-fourier

编辑： Pat Gipper 2024-4-22

I have a very simple task but am not being successful.

I have a PWM generator in simulike runing at a certain frequency and certain duty cycle.

I want to take the fourier analysis of it and plot it in a scope.

What i expect to see is the DC component of the perioid signal... (i think?)

So if i have a period signal PWM signal with a magnitude of say 5 and duty cycle of .5 i expect to see a DC of 2.5 out on my scope.

How can i acomplish this? I have tried a few different blocks in simulink but im not getting what im expecting.

Perhaps my expecatations are wrong.

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Answer 1

Pat Gipper 2024-4-22

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https://ww2.mathworks.cn/matlabcentral/answers/2109506-simulink-to-see-fourier#answer_1445416

fft_fcn.slx

I put it in a Matlab Fcn block and it seems to work. See the attached file for details.

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Pat Gipper 2024-4-22

编辑：Pat Gipper 2024-4-22

The memory block on the bottom, "io" retains a pointer into the top memory block, "buffer", where the latest sample of the input "u" is stored. "buffer" is a circular memory for storing the block of data for calculating the FFT. I tried to store this information within the Matlab function, but it was extremely unhappy with this attempt. I also wanted to make the FFT length a variable, and this was also problematical. I gave up on this for now and am just using a 32 (or was it 64, I forget?) point fixed length FFT.

You can find memory in the discrete selection of Simulink.

Pat Gipper 2024-4-22