THD: estimation using periodogram or fft? I want to estimate the THD of a voltage signal (output from a frequency inverter). At the begining, I need to estimate the power of the signal at frequency domain. To doing so, I should use a periodogram or a FFT.

Matlab uses periodogram in his THD function. I know that are differences between FFT and periodogram, as shown in this question. But, wich method should I use? and why?

Thanks.
Just for answer the question, basically there is no difference at all. My problem was that I've compared a modified periodogram against a FFT. Modified periodogram does have a difference; but simple periodogram doesn't.