Monetarization of the Feasible Operation Region of Active Distribution Grids Based on a Cost-Optimal Flexibility Disaggregation

Abstract

Hierarchical grid control strategies are an appropriate design concept for the coordination of future transmission system operator (TSO) and distribution system operator (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 TSO/DSO 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 TSO grid control. In the context of a local DSO and global TSO market, this article presents an approach for the monetarization of the FOR by a cost structure using metadata from population based aggregation methods. At the local DSO market free bids for the active and reactive power flexibilities by the FPUs stakeholders are assumed. Within the aggregation method multiple FPU flexibility polygons at a single bus are aggregated for a reduction of the search space dimensions. Thereby, 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. The approach can be simply adapted for the coordination of DSO/DSO-interactions regarding hierarchical multi-level grid control strategies.

Review of Methodologies for the Assessment of Feasible Operating Regions at the TSO–DSO Interface

“…A major drawback of the Geometric methods is their failure to integrate the constraints of the DN, which can potentially lead to infeasibilities during dispatch [23]. Even so, Geometric methods remain an important tool in FOR estimation, and can complement RS and OB methods by being used to aggregate the flexibilities of FPUs that are connected to the same bus [21].…”

“…Importantly, via this process, the need for the communication of the topology or the operational status of the DN by the DSO is circumvented. Moreover, the monetization of the FOR (which is discussed in the following sections) can provide a clear pathway to the pricing of the flexibility provided by the DSO to the TSO [19,21].…”

Design and Evaluation of a Multi-level Reactive Power Market

“…Finally, alternatives are required for the quadratic approximation of the cost functions, since it will not always be sufficient in more complex systems. One possibility to communicate prices would be non-convex polygons, which then require more advanced methods to perform the aggregation and optimization, for example meta-heuristic algorithms (Sarstedt and Hofmann, 2022). providers send their planned active power feed-in to the grid operator.…”

“…Some multi-level reactive power markets can be found in literature that focus on both technical as well as economical aspects. Sarstedt and Hofmann (2022) expand their previously mentioned approach by assigning costs to the feasible operation region at the grid coupling point and therefore allowing for its monetization. Doostizadeh et al (2018) determine the reactive power flexibility range and additionally an EPF for a distribution grid, by carrying out several power flow calculations.…”

Linear Optimization Based Distribution Grid Flexibility Aggregation Augmented With OLTC Operational Flexibilities

“…Application of the FOR from the MV grid level for congestion management at the HV grid level is demonstrated in [20]. A mixed integer linear programming based cost-optimal disaggregation of the FOR based flexibility provision addresses the flexibility market characteristics [21].…”