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High frequency grid impedance analysis by current injection

The impedance of the electrical grid is frequency and time depending. Therefore it is very useful to know its value in the frequency range between grid fundamental frequency and frequencies in the kHz-range. The proposed grid impedance analysis contributes to optimize energy feed especially from decentralized converter equipped renewable sources. This paper presents an advanced impedance measurement system with a high frequency range for the energized electrical low voltage grid. A sinusoidal current of predetermined frequency is injected into the grid. The grid impedance at that frequency is calculated from the measured magnitude and phase of the injected current and resulting voltage. The measurements are executed at nearby frequencies to produce nearly continuous impedance versus frequency characteristic. The basic concept and a prototype of test equipment are presented.