Read in b-phase current from COMTRADE file and scale properly.

Step 1: Define sampling frequency (multiple of 2) and build a waveform with several component frequencies.

N samples per cycle

C cycles of fundamental (needs to be greater than 4 for this sheet).

Step 2: Perform the DFT calculation, resulting in a real and imaginary vector.

Slides a DFT window N samples wide

along the entire waveform. It slides along

in one sample steps. The DFT calculation

starts after the first complete fundamental

cycle of samples has been acquired.

Scale the magnitude of the end frequency bins of the real DFT vector.

Calculate magnitude of component frequencies in the DFT and scale properly.

Get rid of zeros if present to allow arctan calculation (avoid zero in denominator).

Compute phase angles and zero those that

are very near zero for clean display.

Correct phase angle of zero frequency component (DC).

Correct results of arctan computation

of frequencies above zero.

Step 4: Rebuild the waveform by using the results of the DFT (magnitude and phase angle of the component frequencies).

Russell W. Patterson, P.E.

Manager, System Protection & Analysis

Tennessee Valley Authority

rwpatterson@tva.gov

Reference: "The Scientist and Engineer's Guide to Digital Signal Processing" by Steven W. Smith

ISBN: 0-9660176-3-3, Website: www.DSPguide.com