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I have been working on a project to design a Phasor Measurement Unit(PMU) in Simulink. And one of the steps involves taking the first harmonic from the FFT block output array(The FFT block itself takes a phase signal as input). I am having trouble figuring out which element in the output array corresponds to the first Harmonic component.

I obtained a simulink file from the internet which uses the element u(2,1,1) from the FFT output array as the First Harmonic array.

A screenshot of the block in question.

If I am reading this correctly this denotes the the element in the 2nd row of the 1st column of the array(No idea what the Third 1 if for?).

My question to all this, how to understand that the element in u(2,1,1) denotes the first harmonic component?

Phil Goddard
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Abrar Hossain
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    The block is using standard indexing notation to get the element from the first 3 dimensions of a 3D array. If your data is only a 2D array then you don't need the 3rd `1`. The `FFT` block can generate N-D arrays, so whoever put the model together may have been using it to get a 3D array as output (of the FFT block) and hence needed the 3rd index. – Phil Goddard Mar 22 '19 at 14:39
  • And the element in the u(2,1,1) position alaways denotes the 1st harmonic component? – Abrar Hossain Mar 23 '19 at 02:15
  • You'll need to read the doc for the FFT block to confirm how it orders its output. – Phil Goddard Mar 23 '19 at 03:04

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