Parameterisation of superordinate grid representations in the calculation of feasible operating regions

Feasible Operating Regions (FORs) represent the active and reactive power flexibility potential of a grid at its interconnection points with the superordinate grid and can therefore be utilised for providing ancillary services across voltage levels. In meshed grid topologies with multiple interconnection points, mutual effects between the grids necessitate an accurate representation of the superordinate grid in FOR calculations. This paper proposes ak-means-based parameterisation of a distributed slack bus. In this approach clusters represent groups of similar voltage angle differences occurring at the interconnection points over time. This method achieves comparable accuracy with as few as three predefined clusters compared to a parameterisation of the distributed slack bus by an exact EHV/HV grid model in each time step. Furthermore, it is investigated whether enhancing the accuracy of the FOR calculation can be achieved by replicating the superordinate grid topology in the immediate vicinity of the interconnection points, by three different scenarios. However, the findings reveal that integrating selected lines from the superordinate grid does not improve accuracy due to the inability to replicate the power flow in the superordinate grid.