Reasons behind this project
Power system networks are undergoing a rapid transformation due to the increasing integration of renewable energy sources (RES), decentralization of electricity generation, and the gradual retirement of conventional synchronous generators. These changes introduce significant uncertainty into grid operation and reduce the traditionally available reactive power flexibility. At the same time, the growing share of inverter-based resources has made maintaining secure voltage profiles across all voltage levels more challenging.
In particular, when the sub-transmission network (e.g. 110 kV) becomes lightly loaded, overvoltages may appear and propagate to the transmission network, too. High solar generation in the distribution network can cause reverse power flows and overvoltages that the transmission system alone cannot compensate. Additional issues such as the inability of medium-voltage transformer tap changers to respond automatically, and inverter limitations that often exclude mandatory reactive power support, further complicate voltage control.
These conditions highlight the growing need for coordinated activation of reactive power capabilities across both transmission and distribution network. While local solutions like compensators, FACTS devices, or enhanced tap changer control can provide partial relief, system-wide reliability increasingly depends on joint TSO-DSO coordination, especially in real time and under high RES penetration.
However, the level of coordination and information exchange between TSOs and DSOs in Europe varies significantly between countries. In some cases (e.g., Slovenia) a single entity, i.e., ELES, operates jointly the transmission and distribution system. However, in other countries there is complete decoupling between the transmission and distribution operators with minimal information exchange. Hence, the topic of TSO/DSO coordination for voltage control calls for different coordination schemes, depending on the operational coordination framework.
Objectives
The overarching objective of U-man is to investigate the different schemes that can be developed to enable TSO-DSO coordination.
– Categorization of the different TSO/DSO coordination frameworks that can be implemented, by defining the various actors, the interfaces, the required information exchanges and the control actions.
– Development of at least two of the various coordination schemes and testing in simplified use cases.
– Testing and validation on realistic test systems and through pilot implementation.
– Analysis of coordination and synergies with other services provided through TSO/DSO coordination.
Project partners
The project team is currently being defined and the project is open to additional partners.
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