Single-Phase Phase Angle Measurements in Electric Power Systems

Computation of phase angles using the discrete Fourier transform (DFT) algorithm has been proven to be sufficiently accurate in a variety of power system applications when the input signal is three-phase voltage and the voltage frequency is near the nominal value. However, the performance of the DFT algorithm in time of the singe-phase voltage input with a large frequency excursion so far has not been well explored, much less documented. This paper briefly discusses the importance of the synchronized phase angle measurement in power systems, and brings up the necessity of research on single-phase measurement systems. The performance of the DFT algorithm in power system phase angle measurements is thoroughly analyzed. Corresponding rectifying methods, including quasi-positive-sequence DFT and offset compensation, are proposed and examined by relevant numerical simulations and necessary laboratory tests. The results of the simulations and tests show a perfect match between the derived equations and the phase angle data, and thus verify the effectiveness of the proposed algorithm, which is believed to be able to greatly improve the performance of DFT in the aspect of phase angle calculation when severe power system upsets with remarkable frequency excursions are present.