This paper describes interpolated discrete Fourier transform (IpDFT) for parameter estimation of sinusoidal and damped sinusoidal signals analyzed with a sin α (x) window. For α = 0, 2, 4, . . . sin α (x) windows are Rife-Vincent class I (RVI) windows, for which IpDFT algorithms are known. We present a new IpDFTs for α = 1, 3, 5, . . .. The bias-variance trade-off of the proposed IpDFT fits between results offered by RVI windows, e.g., for α = 1, we get higher noise immunity than Hann (RVI order 1, α = 2) window and lower bias than rectangular (RVI order 0, α = 0) window.Index Terms-Discrete Fourier transform (DFT), frequency and damping estimation, frequency domain measurements, interpolated DFT, signal processing, windowing.
The paper presents a new method for simultaneous tracking of varying grid impedance and its uncertainty bounds. Impedance tracking consists of two stages. In the first stage, the actual noise estimate is obtained from least squares (LS) residua. In the second stage, the noise covariance matrix is approximated with the use of residual information. Then weighted least squares (WLS) method is applied in order to estimate impedance and background voltage. Finally uncertainty bounds for impedance estimation are computed. The robustness of the method has been verified using simulated signals. The proposed method has been compared to sliding LS. The results have shown, that the method performs much better than the LS for all considered cases, even in the presence of significant background voltage variations.
Quality of power supply in power distribution systems requires continuous measurement using power quality analyzers installed in the grid. The paper reviews the published methods for optimal location of metering points in distribution systems in the context of power quality metering and assessment. Three methods have been selected for detailed analysis and comparative tests. It has been found that utilization of the methods is possible, but their performance varies highly depending on the test grid’s topology. Since the methods rely on the state estimation approach, their performance is strictly related to observability analysis. It has been found that standard observability analysis used for typical state estimation problem yields ambiguous results when applied to power quality assessment. Inherited properties of the selected methods are also analyzed, which allows for the formulation of general recommendations about optimal selection of metering points in a distribution system.
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