Investigating the accuracy of feasible operating regions in meshed grid topologies by using grid equivalents

Feasible Operating Regions (FORs) are a tool for estimating possible active and reactive power capabilities of subordinate active distribution networks and can contribute to the provision of system services across voltage levels. A current field of research in this context is the FOR calculation at meshed TSO/DSO interfaces. Previous works have focussed on the calculation of FORs on the DSO side but have neglected the mutual effect with the TSO. This work quantifies the influence of the superordinate extra-high-voltage (EHV) grid on the FOR calculation in the high-voltage (HV) level. From this, it is deduced that a detailed representation of the EHV grid is necessary and two approaches using distributed slack modelling and an Extended-Ward equivalent are presented. Both are compared with the typical literature model, the modelling using a single slack bus and the calculation of an exact overall model of the EHV/HV level. It is shown that both, modelling via the distributed slack bus and via the Extended-Ward equivalent, contribute to increasing the accuracy of the FOR calculation at the TSO/DSO interface.