Impacts of Equivalent Dynamic Grid Impedance on Inverter Based Resources Plant

Nowadays large number of inverter-based resources (IBRs) are integrated into the grid at a single connection point as an IBR plant. Due to the increase in number of IBRs, the effect of IBRs on the grid impedance fluctuation as well as the effect of variation in grid impedance on the IBRs became significant. Several abnormal events have been reported due to this phenomenon. In this article, the reason of these abnormalities are analyzed from a novel point of view. The equivalent dynamic grid impedance concept is introduced to analyze the effect of multiple IBRs and their injected current into the grid. Also, the effects of the equivalent dynamic grid impedance on the IBR design, control, operation and stability are analyzed. A frequency sweep simulation model is used for the verification of the mathematical representation of the concept. The results show that, the number of IBRs changes the grid impedance i.e. grid strength. Conversely, the grid impedance variation has multiple effects based on different grid connected filter, such as PCC voltage and harmonic stability and IBR controller stability.