Abstract
This paper proposes a near to real-time local market to provide reactive power to the transmission system operator (TSO), using the resources connected to a distribution grid managed by a distribution system operator (DSO). The TSO publishes a requested reactive power profile at the TSO-DSO interface for each time-interval of the next delivery period, so that market agents (managing resources of the distribution grid) can prepare and send their bids accordingly. DSO resources are the first to be mobilized, and the remaining residual reactive power is supplied by the reactive power flexibility offered in the local reactive market. Complex bids (with non-curtailability conditions) are supported to provide flexible ways of bidding fewer flexible assets (such as capacitor banks). An alternating current (AC) optimal power flow (OPF) is used to clear the bids by maximizing the social welfare to supply the TSO required reactive power profile, subject to the DSO grid constraints. A rolling window mechanism allows a continuous dispatching of reactive power, and the possibility of adapting assigned schedules to real time constraints. A simplified TSO-DSO cost assignment of the flexible reactive power used is proposed to share for settlement purposes.

Abstract
Renewable energy communities (REC) and local energy markets (LEM) emerge as entities capable, not only to promote the penetration of renewable energy sources into lower levels of the grid, but also to manage distributed energy resources (DER) and local energy exchanges between small players. This paper proposes a benefit assessment among different regulatory frameworks for LEM, considering network constraints and a virtual storage unit. Results show significant savings can be achieved, even without storage. Therefore, the continuous increase of DER can have considerable grid impacts if not complemented by other structures as storage or by alternative market services like flexibility.

Abstract
EU-SysFlex H2020 project aims at developing and testing innovative tools for the integration of high levels (above 50%) of renewable energy sources (RES) in the pan-European Electricity system. Those high levels of RES will increase the need for new sources of flexibility to support the system services, since there will be a decreasing number of conventional power plants connected to the grid, traditionally the main providers of these services. In this context, this study describes the Flexibility Hub (FlexHub) concept, part of the EU-SysFlex Portuguese demonstrator, consisting of a platform of tools managed by the distribution system operator to facilitate market-based flexibility provision to the transmission system operator (TSO) using resources connected to the distribution system. The FlexHub includes the provision of active power flexibility to the TSO (with an extended restoration reserve market concept), an essential tool to help the TSO balancing the grid, being a replicable concept that will become increasingly relevant in a future with a high share of decentralised assets connected to the distribution grids.

Abstract
The study at hand describes the state of the art regulatory framework for managing the distribution system operator (DSO)/transmission system operator (TSO) interface including information about the available flexibility data and access rights of the different grid operators. It describes a possible future procedure to manage this interface using software tools to support this coordination performing grid analysis and providing active as well as reactive power flexibility information at several TSO–DSO interconnection points. The proposed study gives a short overview of two optimisation approaches/software tools with different application functionalities, developed and adapted to meet the demands coming up with such tasks, performed within the European project ‘EU-SysFlex’. Both tools contribute to the objective of optimising available flexibility resources connected to meshed distribution grids with multiple grid connection points to the transmission grid. The investigations/calculations are performed using a real existing high-voltage grid of MITNETZ STROM. Using the outputs, provided by both tools, the demonstrator aims at providing beneficiary results for the discussion of how to evolve the regulatory framework. The functionality of the developed algorithms of both optimisation tools is evaluated and investigated by means of a live field test.

Abstract
With the energy transition at sight and the EU renewable energy source integration ambition, the EU-SysFlex project aims at defining a set of advancements in the electric system that drives us towards that direction. With the increasing decentralisation and granularity of the generation facilities, local generation will gain a determinant role in the provision of future local and global systems services. This study presents an overview of a framework for a local market for reactive power control that will be implemented and demonstrated under a real scenario in a Portuguese demo site. The demonstration includes a set of capacitor banks of the distribution system operator (DSO) and two wind farms of a wind power generation operator. This local reactive power market consists of a close to real-time continuous intraday local market managed by the DSO, with 15 min delivery time to increase temporal granularity, and with 7 h delivery horizons with complex bids to allow more flexible assets operation. Market agents can also correct future previously scheduled positions by participating themselves as sellers or buyers of capacitive or inductive reactive power, providing a more flexible framework.

Abstract
This paper presents a methodology to estimate flexibility existing on TSO-DSO borderline, for the cases where multiple TSO-DSO connections exist (meshed grids). To do so, the work conducted exploits previous developments regarding flexibility representation through the adoption of active and reactive power flexibility maps and extends the concept for the cases where multiple TSO-DSO connection exists, using data-driven approach to determine the equivalent impedance between TSO nodes, preserving the anonymity regarding sensitive grid information, such as the topology. This paper also provides numerical validation followed by real-world demonstration of the methodology proposed.