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

Inhalt:
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, impedance 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 different voltage levels, the impedance for the cables and transformers can be calculated as well. Furthermore, the propagation of harmonics across the grid levels from low voltage to high voltage can be investigated.