IMPACT OF THE SELECTION OF GRID-FORMING CONVERTERS ON THE STABLE OPERATION OF MEDIUM VOLTAGE TEMPORARY ISLANDED MICROGRIDS

Abstract

Due to the increasing generation by distributed units at the medium and low voltage level, a temporary islanded microgrid operation of distribution grid structures becomes possible. The islanded operation can be advantageous during a blackout of the transmission grid, as the supply of customers can be ensured using local generation units. In order to enable an autonomous operation, at least one grid-forming unit is required. In this paper, a distributed grid-forming control concept based on several droop-controlled grid-forming converters is focused. By conducting dynamic time domain simulations and applying load changes in the CIGRE medium voltage benchmark grid, the impact of the amount and the positioning of the grid-forming converters is investigated. A particular focus is placed on the interactions between the grid-forming and the existing grid-following converters, which are implemented to behave according to the German grid code VDE-AR-N 4110. The results show a beneficial behaviour of the distributed grid-forming control concept, if no dominant grid-forming converter coupled generation unit is present in the grid. This is due to the fact that the load changes are initially shared among the grid-forming units. Furthermore, an electrically closer positioning of the grid-forming converters can balance that initial power sharing.