What is difference if I calculate THD for singlle no of cycle or large no of cycle using fft analysis in powergui block.

I calculated THD for the voltage signal using both THD block and also using fft analysis from powergui. When I mentioned the no of cycle=1, the value of THD was acceptable and also equal to the value given by THD block. But if I increase the no of cycles i.e around 20-50, then the value of THD is way high i.e. around 300%. BUt from the harmonics spectrum, I can see that there is not much presence of higher order harmonics and my waveform isn't distorted at all. What may have gone wrong?

[Cihat Sonmez]

Hi sir,

Do you already have a answer to this question. I am facing the same problem.

Thank you in advance!

[Saïd DAOUDI]

I advise you to check these two questions :

https://fr.mathworks.com/matlabcentral/answers/100100-why-is-the-total-harmonic-distortion-value-different-while-using-the-signal-thd-block-vs-the-powerg?s_tid=answers_rc1-1_p1_Topic

and

https://fr.mathworks.com/matlabcentral/answers/76397-how-to-calculate-total-harmonic-distortion-using-fft-analysis-tool-of-power-gui-block?s_tid=answers_rc1-3_p3_Topic

I hope it helps

Saïd