Grid-impedance estimation in high-frequency range with a single signal injection using time–frequency distribution

Abstract

Grid impedance is an important parameter in most power system applications such as power quality analysis of smart grids. In this study, a new time–frequency distribution is employed for grid-impedance estimation in high-frequency range using a single rectangular pulse injection. There is no compatibility level for harmonics within the frequency range of 2–150 kHz which is the most important issue in the international standardisation committee. Compatibility level is defined based on harmonic emission and immunity levels of grid-connected equipment. Therefore, knowledge of grid-impedance characteristics over the frequency range of 2–150 kHz is very important to estimate the level of distortion caused by grid-connected equipment and defines future regulations and standards. For impedance estimation, a pulse must be injected to the grid, then the current through and voltage at a point of common coupling are measured. The measurement duration must be long enough to consider the transient state. The most appropriate shortest measurement duration is selected from the time–frequency plane using Wiener entropy. Test and simulation results validate the accuracy of the proposed method for grid-impedance estimation in high-frequency range.