Module 9 : Numerical Relaying II : DSP Perspective

Lecture 35 : Computation of Phasor from Discrete Fourier Transform

35.1 DFT of a Sinusoid
 

Consider a sinusoidal input signal of frequency , given by

 

  (1)
  This signal is conveniently represented by a phasor
    (2)
 

Assume that is sampled times per cycle such that . Then,

  (3)
 

and fs = Nf0. In the transform domain, transformed components are separated by . Thus, choice m = 1 corresponds to extracting the fundamental frequency component. The Discrete Fourier Transform of contains the fundamental frequency component given by

    (4)
 
    (5)
  where,   (6)
   
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