Fourier Transform with frequency spacing

I would like to know how to correctly calculate signal's Fourier Transform which is knownly composed of the frequencies which are evenly spaced. s1(f1), s2(f2) and s3(f3).

s1, s2, s3 are signals.

s = s1 + s2 + s3

f1, f2, f3 are its frequencies e.g. 100 kHz, 101kHz and 102kHz.

Now other signals s2, s3 (101kHz, 102 kHz) are modeled as base frequency harmonics .. it works BUT those other signal are in realiy not as base frequency harmonics ... I would like to know how to use "Fourier Analysis" block to extract other frequency components (101kHz, 102kHz) which are not of base frquency related?

Thank you!

Answer 1

[Sudarsanan A K]

Hello Peter,

The primary purpose of Fourier Analysis block is analysis of the magnitude and phase of the fundamental frequency and its harmonics in a power system.

For your case with distinct frequencies ( kHz, kHz, and kHz) that are not harmonics of the base frequency (which is kHz), the Fourier Analysis block from Simscape Electrical may not be the right choice since it is designed to analyze signals relative to a fundamental frequency and its harmonics.

However, if you still want to use the Fourier Analysis block to analyze your signal, you will need to set the fundamental frequency to a value that would allow the block to consider your frequencies of interest as harmonics. For instance, if you set the fundamental frequency to 1 kHz, then kHz, kHz, and kHz would be the , , and harmonics, respectively. But this is a workaround and not the intended use of the block.

To analyze a signal composed of non-harmonic frequencies in Simulink, you are better off using the FFT-based approach with the FFT block from the DSP System Toolbox. This will provide you with a frequency spectrum of the entire signal, showing all frequency components present, not just those related to a fundamental frequency and its harmonics.

For further details and examples of applications, please refer to the following documentation from MathWorks:

• Fourier Analysis block: https://mathworks.com/help/sps/ref/fourieranalysis.html
• FFT block: https://mathworks.com/help/dsp/ref/fft.html

I hope this helps!