An Open-Loop Fundamental and Harmonic Phasor Estimator for Single-Phase Voltage Signals

This article proposes a novel technique for fundamental and selective harmonic phasor estimation of a single-phase voltage signal based on open-loop voltage signal processing approach, under adverse distorted conditions. At heart, a modified fast discrete Stockwell transform (FDST) is used for the phasor estimation. The performance of the FDST is improved by incorporating a new frequency-dependent Gaussian window for capturing the time-localized variations of individual frequency component. The modified window has four parameters, which are selected based on the statistical properties of the given input voltage signal. Furthermore, under off-nominal frequency conditions the spectral leakage problem, faced by the S-transform, is avoided by proposing a modified sample value adjustment based preprocessing stage. Various static and dynamic tests were considered according to the IEEE Standard 1159, IEEE Standard C37.118.1a-2014, and EN-50160 standards under harmonics and interharmonics scenarios. The performance of the proposed method is validated using synthetic voltage signals, simulated voltage signals on 6-bus microgrid model developed in power system computer aided design (PSCAD), and hardware implementation on dSPACE 1103. The rigorous test cases reveal that the proposed phasor measurement unit has a good adaptability to grid frequency drifts, a good harmonic and dc-offset rejection capability, and a very good steady state as well as dynamic response.