Hello, just to be clear- is the signal you are trying to analyze a single (frequency) pure sine wave, therefore with no harmonics? If so, I’m not sure a DFT would be very interesting in this case?

It looks like you are using an older version of PLECS as the Fourier Transform component has recently been updated (as in my attached model). I recommend that you update to the latest version as this is now easier to use. Regardless, I’m not sure your model makes sense still- what is the duration of your simulation? If it is the default of 1 second, the sampling time of 8 seconds shown in your image will not be meaningful. Further, I would need to see your model, but I think your fundamental frequency of the averaging is set to 1/(8*8) = 1/64 Hz.

In my attached PLECS Standalone model I have two frequencies overlaid of 10 and 20 Hz and the Fourier shows the expected results of the first (base) and second harmonic in the Scope.

Let me know if this feedback helps to clarify your questions.

Hi Kris, Thanks for your response. I made a mistake the first circuit. it the sampling frequency is 1/8 s and the fsignal=1Hz.
might I ask what is the fundamental frequency?

If the frequency of the signal you are sampling is 1Hz, then that is the fundamental frequency for the FT block. Or am I not understanding your question?