An effective hybrid algorithm for the simultaneous measurements of harmonic and flicker to mitigate the effect of system frequency variation

In this paper, the effects of the system frequency variation on the harmonic and flicker calculations using DFT are determined. The theoretical results illustrate that serious error are caused in the flicker computation even if the frequency variation is trivial. Therefore, an improved hybrid algorithm is proposed to mitigate the frequency variation effect. This algorithm incorporates the Prony-based frequency evaluation scheme into a continuous-wavelet-transform-(CAVT-) based flicker calculation method. Since the system frequency variation has minor effect on the DFT-based harmonic calculation, the fast Fourier transform (FFT) is used in harmonic measurement. Therefore, the hybrid algorithm combining FFT, Prony, and CWT schemes can be very effective for the simultaneous measurements of harmonic and flicker. The results obtained from simulation and field signal tests validate the performances of the algorithm.