The paper presents research results on a novel algorithm that allows estimation of parameters associated with the specific voltage fluctuation sources in the power grid, which change their operating state with frequency of up to 150 Hz. The proposed algorithm allows estimating the rate of changes of the disturbing load state, the amplitude, and shape of voltage changes caused by specific sources of disturbances. The decomposition of the estimated AM modulation voltage signal in the power grid is used to implement the algorithm. The algorithm uses a carrier function estimator, which allows research on disturbing loads that change their operating state with frequency greater than the power frequency. The Enhanced Empirical Wavelet Transform is used for the decomposition, which allows recreating selected parameters, considering random operation of disturbing loads. Accurate recreation of selected parameters will allow selective location of disturbing loads by assessing the propagation of voltage fluctuations caused by specific sources of disturbances. An alternative algorithm has been proposed with coding of voltage changes to voltage fluctuation indices determined from the estimated AM modulation signal of voltage, allowing reducing the necessary memory of the measuring device. Experimental studies have been conducted for the proposed algorithms, considering rapid voltage changes.

This paper presents the preliminary research results on a novel method of AM demodulation that allows estimation of the modulating signal at a frequency higher than that of the carrier signal. The need for a new method from the perspective of research on sources of voltage fluctuations is first explained. Then, a comparison is carried out between the estimation of the modulating signal based on the currently used demodulator in the IEC flickermeter signal chain, the FIR Hilbert filter, and the proposed method with the carrier signal estimation. The correctness of the recreation of the frequency of the modulating signal, as well as, the signal amplitude and shape were considered in the comparison. The influence of the deformation of the carrier signal on the estimation error of individual demodulation methods was investigated. The metrological interpretation of the results obtained from the numerical simulation and experimental research is discussed, and the conclusions are presented.

Currently, electricity is treated as commodity that should be delivered from a distributor to a consumer with a certain quality. The power quality is defined by the set of measures with specific limit values. One of the basic measures is the Total Harmonic Distortion (THD), which allows to assess the level of the voltage distortion. The measurement of THD ratio should be carried out in accordance with the normative specification. It is assumed that this requirement is met by class A power quality analyzers. Currently, measures are taken to monitor power quality in a large number of measurement points with the use of smart energy meters that are part of the Advanced Metering Infrastructure (AMI). The paper presents the problem of THD ratio measurement by AMI meters if voltage fluctuations occur. In such situation, inconsistency in measurement results of AMI meters and class A power quality analyzers occurs. The problem is presented on the basis of laboratory study results in which disturbances in power grid are recreated.

The article presents the novel findings on the dependence of voltage fluctuation severity on voltage distortion caused by power electronic loads. The results indicate the need to modify the recommended limitation of the IEC flickermeter bandwidth to cut-off frequency at least 450 Hz by the IEC standard, to consider the possible obnoxious voltage fluctuation caused by power electronic devices. The real voltage distortion of the “clipped sine” or “sharpened sine” type, resulting from nonlinear currents, the flow of which is forced by power electronic devices, was considered in the research. The basics of indicator P _st /P _lt measurement by IEC flickermeter are discussed, and the influence of sinusoidal supply voltage distortion on the indicator P _st measurement was investigated. The analytical model of IEC flickermeter signal chain was proposed to explain the influence of supply voltage distortion on the indicator P _st measurement. This model was verified by comparing the results of numerical simulations and laboratory measurements.

The current study presents a novel approach to the selective identification and localization of voltage fluctuation sources in power grids, considering individual disturbing loads changing their state with a frequency of up to 150$\mathrm{Hz}$. The implementation of the proposed approach in the existing infrastructure of smart metering allows for the identification and localization of the individual sources of disturbances in real time. The proposed approach first performs the estimation of the modulation signal using a carrier signal estimator, which allows for a modulation signal with a frequency greater than the power frequency to be estimated. In the next step, the estimated modulating signal is decomposed into component signals associated with individual sources of voltage fluctuations using an enhanced empirical wavelet transform. In the last step, a statistical evaluation of the propagation of component signals with a comparable fundamental frequency is performed, which allows for the supply point of a particular disturbing load to be determined. The proposed approach is verified in numerical simulation studies using MATLAB/SIMULINK and in experimental studies carried out in a real low-voltage power grid. The research carried out shows that the proposed approach allows for the selective identification and localization of voltage fluctuation sources changing their state with a frequency of up to 150$\mathrm{Hz}$, unlike other methods currently used in practice.

Power quality assessment is a complex measurement task, requiring the usage of a system with suitable metrological properties. This complex measurement task in the real power grid is performed with the use of power quality analysers that measure and record the parameters determining the power quality. The paper presents selected research results for a class A power quality analyser in the specially prepared measurement system containing measuring instruments calibrated by the Main Office of Measures. The measurement results were completed with a presentation of the uncertainty budget. The influence of the phenomenon of spectrum leakage on metrological properties of the tested power quality analyser was considered in the paper. To assess this influence, the simulation studies with the use of MATLAB and the experimental studies were carried out for selected test signals. The Metrological interpretation of the research results is presented in the paper.