The stability and security of the traditional electrical power systems is largely based on the inherent properties of synchronous generators (SGs). Such properties are: the grid-forming capability, the inertia and damping of transients and the provision of large currents during faults. The growing penetration of converter-interfaced (thus inertia-less) Distributed Renewable Energy Sources (DRES) will eventually replace dispatchable SGs and increase power volatility, causing large frequency deviations and voltage regulation problems.
The increase of SG spinning reserves, the grid reinforcement and the use of central electric energy storage systems are some obvious solutions proposed to tackle this problem. However, due to their centralized approach and high cost, these actions can be undertaken only centrally by the Transmission System Operators (TSOs) and Distribution System Operators (DSOs). By adopting a unified bottom-up approach, EASY-RES will develop novel control algorithms for all converter-interfaced DRES in order to enable them to operate similarly to conventional SGs and provide new Ancillary Services (AS) to the distribution and transmission grid such as inertia, damping of transients, reactive power exchange for voltage regulation purposes, fault ride through and fault-clearing capabilities, and adaptable response to primary and secondary frequency control. These new functionalities will be transparent to all grid voltage levels (low-, medium- and high-voltage).
The EASY-RES approach is based on the segmentation of the distribution network into small Individual Control Areas (ICAs), where the DRES and properly sized storage systems will be optimally coordinated via suitably designed ICT infrastructure to provide the aforementioned ASs in a bottom-up approach: prosumers and independent RES producers will provide ASs to DSOs and the aggregation of these ASs will be provided by the DSOs to TSOs. By evaluating the costs and benefits of the developed functionalities, viable business models will be developed for relevant stakeholders such as DSOs, TSOs, Balancing Service Providers, independent electricity producers, etc. Finally, modifications to the existing grid codes and market regulations will be proposed for the integration of the developed AS at the distribution system.
Technical description and implementation
In EASY-RES approach, the distribution grid (all of it or part of it) is considered as an Individual Control Area (ICA) containing MV voltage feeders and LV feeders, which can form LV microgrids (μG) as shown in Fig. 1. The AS can be offered in two layers (Fig. 2): individually by each DRES at the Foundation Layer and in aggregated and coordinated form in the Enabling Layer. The controlled exchange of reactive power by the DRES/BESS and the deterioration of the active power volatility through the BESS is addressed in the first work package (WP1). The AS related to dynamic and transient conditions (inertial and primary frequency response, mitigation of fast changing active power and active harmonic filtering) are addressed in WP2 together with new methods for evaluating the aggregated inertial and PFR that an ICA can offer as function of time.
The FRT capability of the DRES and their contribution to fault-clearing is tackled in WP3 along with new methods for protection coordination under high DRES penetration. The required ICT infrastructure to support the monitoring and control actions at DRES and ICA level will be developed in WP4.
Detailed cost functions (including the investment, operational and maintenance cost) for the provision of the each AS is derived in WP5. These cost functions, together with the AS metrics and quantification methodologies developed in WP1-WP3 will enable the development of new business cases for various stakeholders. The business cases will be based on the provision of the new AS either to the transmission system (in aggregated form) or within the ICAs (individually for each DRES/BESS). Modifications in the current electricity market regulatory framework will be proposed so as to enable the introduction of the new AS at all voltage levels.
All the new functionalities will be tested in WP6 after building new converter prototypes for the DRES. The tests will be conducted at laboratory scale using real-time digital simulations with hardware-in-the-loop capabilities, as well as laboratory modeling of CIGRE benchmark distribution systems. The various KPIs associated with the project objectives will also be evaluated in WP6 through detailed simulations. Suggestions for grid-code modifications will also be suggested so that the new DRES/BESS functionalities are introduced at the distribution grid level.
The dissemination and management activities of the project are dealt with in WP7 and WP8.
The project outcomes will be presented in 66 deliverables, while 31 milestones will track the project progress and achievements. There will be 22 research “products” that will be advanced from TRL 1-3 to TRL 4-5.
The project is expected to improve EU energy security by allowing very high penetration (up to 100%) of RES in the grid with simultaneous decommission of large SG driven by conventional fuels. This fact will also have a large impact on the environment and will contribute to solving the global climate and energy challenges. The high RES penetration will be achieved by making their variable generation more predictable and grid friendly through the coordinated action of the new functionalities of the DRES/BESS and their coordinated control. This impact is expected to be large due to the reasonable additional cost that will be required for the provision of these functionalities. The generic and unified approach followed by EASY-RES in making the DRES/BESS exhibit new functionalities, thereby be able to offer AS, brings cohesion and coherence in the development of new renewable energy technologies. Since the EASY-RES approach will also enable the individual DRES owners to participate actively in the future operation of the electricity grids, it is expected to have socio-economic impact too. As a whole, the EASY-RES results will verify that the policy of the European Commission in supporting larger RES penetrations in the electricity grid and transforming the prosumers into active players of the future smart grids is feasible.