Modelling the Influence of Virtual Inertia in Distribution Systems on Frequency Stability

Due to the decreasing share of synchronous machines in the power grid in the course of the energy transition, the flywheel mass and thus the system inertia decreases. In the event of power imbalances, this counteracts a change in the grid frequency, which is why reduced inertia has a negative effect on frequency stability. In the future, virtual inertia could provide a remedy in the form of suitable control of invertercoupled plants, the effect of which is currently being investigated primarily in islanded grids. The inverter controls require new modeling approaches due to their faster dynamics compared to synchronous machines and the influence of spatial distribution. Furthermore, frequency support has been provided mainly from the transmission grid, where the large-scale power units are connected. Virtual inertia is expected to be provided from the medium and low voltage levels in the distribution grid to a relevant extent. Therefore, in this study the aggregated mean time model will be compared with the detailed model of a distribution system under the influence of virtual inertia placed in the distribution system. Moreover, multiple implementations of virtual inertias are briefly reviewed.