Rogalla, SönkeSönkeRogallaKaiser, SebastianSebastianKaiserBurger, BrunoBrunoBurgerEngel, BerndBerndEngel2022-03-142022-03-142020https://publica.fraunhofer.de/handle/publica/40960210.1109/PEDG48541.2020.92443802-s2.0-85097530483This paper introduces a measurement technique that allows grid-connected inverters to be interpreted as frequency-dependent Thévenin equivalents. By means of this so-called differential impedance spectroscopy it is possible to determine the spectrum of internal harmonic voltage sources as well as the effective frequency-dependent output impedance of an inverter. Having this, one can distinguish between resonance-based and source-driven harmonics, which provides a more useful analysis of harmonic interactions between inverters and the grid. This paper presents the fundamentals and the procedure of the differential impedance spectroscopy, describes a realized test-stand for inverters up to one megawatt and gives exemplary measurement results.enLeistungselektronikNetze und Intelligente SystemeWechselrichter in Netzen621697conference paper