A hybrid digital algorithm for harmonic and flicker measurements

The voltage and current waveforms in an electric power circuit are usually harmonic-distorted and flicker-modulated due to the intermittent operation of nonlinear devices with large capacity. Digital algorithms based on fast-Fourier-transform (FFT) have been widely used for harmonic and flicker measurements. Since the requirements of frequency resolution and range are very different for harmonic and flicker measurements respectively, these measurements are always performed separately. Continuous wavelet transform (CWT) based algorithms were respectively applied to accurate harmonic, inter-harmonic, and flicker analysis, but a common disadvantage of these algorithms is the heavy computational burden. To facilitate the feasibility and practicality of the application, this paper proposes an FFT and CWT hybrid algorithm that can simultaneously accomplish the measurements of harmonic, inter-harmonic and flicker. The performance of the proposed algorithm is validated by the measurement simulations of synthesized signals, and the feasibility is approved by the measurement test of a recorded field signal on an electric arc furnace feeder. The results illustrate that the calculation time of the proposed algorithm can be largely reduced, while the accuracy is still acceptable.