  Hierarchical multi-(voltage-)level grid control strategies are an appropriate
design concept for the coordination of future TSO/DSO- and
DSO/DSO-interactions. Hierarchical approaches are based on the aggregation of
decentralized ancillary service potentials, represented by converter-coupled,
communicable active and reactive power flexibility providing units (FPU) (e.g.
wind turbines) at vertical system interfaces. The resulting PQ-polygon made
available by the DSO for a potential request of ancillary service flexibilities
by the TSO is called feasible operation region (FOR). A monetarization of the
FOR is necessary for the implementation as operational degree of freedom within
higher-level grid control. This paper presents an approach for the
monetarization of the FOR in the context of a hierarchical multi-level
flexibility market by a cost structure using metadata from population based
optimization methods. Multiple FPU flexibility polygons at a single bus are
aggregated for a reduction of the search space dimensions. The main
contribution of the proposed method is the cost-optimal disaggregation of a
flexibility demand to the single FPUs within the aggregated FPU by a mixed
integer linear program (MILP). Therefore, a local flexibility market
considering bids for the active and reactive power flexibilities by the FPUs
stakeholders is assumed. The approach is applied within a case-study of the
Cigr\'e medium voltage system.
