Frequency-Dependent Grid Impedance Measurement on Low-, Medium- and High-Voltage Level

With the increasing expansion of renewable energies, the share of power electronics connected to the grid is also rising. To achieve a high voltage quality in the future, new procedures and methods for the analysis and reduction of harmonics are necessary. It is increasingly found that the grid impedance has a significant influence on the formation and propagation of harmonics of power electronic devices. Therefore, the importance of determining the network impedance is growing considerably. Impedance spectroscopy is a new approach for determining the grid disturbance of converters. It has been shown that harmonics can have two different causes: Source-driven and resonance-driven harmonics. For the evaluation of resonance-based harmonics, knowledge of the grid impedance is required. In the following work, im-pedance spectroscopy is used to determine the frequency-dependent grid-impedance and effective harmonic source given for a point of coupling. The method is applied on grid-side testing for the first time and verified with a simulation and impedance measurements using a conventional grid-impedance measurement device. With measurement devices on dif-ferent voltage levels, the impedance for the cables and transformers can be calculated as well. Furthermore, the propaga-tion of harmonics across the grid levels from low voltage to high voltage can be investigated.