Digital algorithms for measurement of voltage flicker

Abstract
The fluctuation of utility voltage often becomes so serious that the flicker of electrical lighting equipment is visible and sometimes irritable. In order to solve the problems related to voltage fluctuation, many definitions and meters had been proposed and developed. In this paper, these meter principles are categorised, and the digital algorithms used to calculate voltage flicker are discussed. Special attention is focused on the pitfalls of the fast Fourier transform, which is used to analyse the spectrum of voltage fluctuation signals. Since the trivial system frequency deviation may cause serious leakage under proper frequency resolution, the directly digital demodulation method is not suggested. In order to reduce aliasing, a low-pass filter (LPF) is necessary, and the sampling frequency of the analog to digital converter (ADC) must be not less than two multiples of the cut-off frequency of the LPF. The frequency resolution must be raised as much as possible to lower the inherent picket-fence effect, owing to the approximately continuous spectrum distribution of the voltage fluctuation. Based on the above considerations, a developed microcomputer-based instrument system prototype was used to validate the operation of the proposed algorithm, by the voltage-flicker measurement of a simulated voltage-flicker generator and an arc-furnace feeder.