Aggregation of the ancillary service potentials of the distribution system level at multiple vertical system interfaces in the context of hierarchical multi-level grid control strategies

• Applicant: Professor Dr.-Ing. Lutz Hofmann
• Subject Area: Electrical Energy Systems, Power Management, Power Electronics, Electrical Machines and Drives
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 497762376

The transition of the electric power system results in a massive integration of decentralized energy resources (DER), especially in the distribution grids, as well as to a temporary displacement of large thermal power plants in the transmission grids with a resulting reduction of their ancillary service potentials. This leads to an increasing number of e.g. cost-intensive redispatch measures and to a need for grid expansion measures in the future. In contrast, the distribution system operators (DSOs) have access to the ancillary service potentials of the DER and electrical energy storage systems as distributed active and reactive power flexibilities that can be controlled according to demand. These flexibility potentials can be used by the DSOs to optimize their own system operation as well as for the provision of ancillary service potentials to the higher-level system operator, e.g. a transmission system operator (TSO). An intensification of TSO/DSO- and DSO/DSO-interactions at the vertical system interfaces is necessary to enable the use of these flexibility potentials in the different system levels. For this purpose, hierarchical multi-level grid control strategies represent a suitable concept. Hierarchical approaches are based on the aggregation of all distributed flexibility potentials of a DSOs system at a single system interface to a corresponding active and reactive power flexibility region (PQ-polygon), the so-called Feasible Operation Region (FOR). The FOR represents the flexibility potentials of the DSO for adjusting the vertical active and reactive power flows within a specific operating point. Within the operational management of the TSO the flexibility demand required from the lower-level system is determined within the limits of the FOR and communicated to the DSO. Within the framework of a cascading process, distributed flexibility potentials can thus be made available to the higher-level system operators at the vertical TSO/DSO- or DSO/DSO-system interfaces to ensure the stability of the overall system. Methods for the determination of the FOR discussed in literature so far are only applicable for a single vertical system interface. In the case of multiple vertical system interfaces, e.g. between a TSO and a DSO, complex vertical and horizontal dependencies between the interface variables arise due to the meshed grid structure. Thus, there are also corresponding dependencies between the FORs of the interface busses. The objective of the proposed research project is the development of methods and procedures for the aggregation of the flexibility potentials of flexibility-providing DER in lower-level systems at multiple vertical system interfaces as multidimensional FORs. A second objective is the implementation of these multidimensional FORs in the operational management of the higher-level system operator in the context of hierarchical multi-level grid control strategies.

• DFG Programme: Research Grants