Under the term "operation along the characteristic", the current Technical Connection Rules (TCRs) define requirements for power plants that are not subject to any stability criteria. They ensure neither grid-forming nor system-supporting behaviour. The interconnected power system or separated subsystems can tolerate a certain penetration of power plants that are not of the grid-forming kind as long as the stability in total is ensured. The generation units without grid-forming behaviour are expected to at least include system-supporting capabilities. However, it is fundamental that controller structures and parameterisations are determined based on defined stability criteria. At the heart of this approach is the frequency control for active power balancing and the voltage control.
Further development of regulation
The basis for system stability is the separate network operability of power-generating and power-consuming power plants (storage units, PGCUs). Therefore, new requirements are currently being defined in the TCRs under the cooperation of the FNN committees. System-supporting capabilities for new plants play a vital role here. In future, these will be anchored as a minimum requirement in the TCRs. Since Germany plans to phase out conventional power plants until 2030, renewable power plants must be equipped with the capabilities of these power plants. This affects grid-forming capabilities in particular. Therefore, new requirements must be defined and implemented quickly to allow new power-generating and power-consuming power plants to provide these capabilities in the future. Such requirements are currently being developed jointly by all players in the VDE FNN and will be published in an FNN Guideline in 2023.
VDE FNN contributes to an in-depth and technical discussion at the European level to define and address aspects potentially endangering system stability. System-supporting behaviour of power plants is critical for the safe operation of the interconnected grid and should be taken into account in the revision of the European Network Codes, in particular the NC RfG. The VDE FNN Infopaper "Future requirements for power system stability" was submitted to the ACER consultation as a proposed amendment to the NC RfG in November 2022.