Distribution Grid Power Flexibility Aggregation at Multiple Interconnections between the High and Extra High Voltage Grid Levels

The energy transition towards renewable based power provision requires improved monitoring and control of distributed energy resources (DERs), installed predominantly at the distribution grid level. Due to the gradual phase out of thermal generation, a shift of ancillary services provision like voltage control, congestion management and dynamic support from DERs is underway. Increased planning for procurement of ancillary services from underlying grid levels is required. Therefore, provision of flexible active and reactive power potentials from distribution system operators to transmission system operators at the vertical system interface is a subject of current research. At present, provision of active and reactive power flexibilities (PQ-flexibilities) across radial system interconnections are investigated, which involves a single transformer branch interconnection across two different voltage levels. Inclusion of multiple interconnections in a meshed grid structure increases the complexity as proximal interdependencies of interconnections to PQ-flexibilities require consideration. The objective of this paper is to address the flexibility aggregation across multiple vertical interconnections. Alternating current power transfer distribution factors (AC-PTDFs) are used to determine the power flow across the interconnections. Subsequent integration in a linear optimization environment controls the interconnection power flows (IPF) using a weighted objective function. Therefore, power flow regulation is enabled according to the requirements and specifications of both the underlying and overlaying grid level. The results show interdependent concentric flexibility regions or Feasible Operating Regions (FORs) in accordance with the manipulation of the weighted objective function.