Abstract
Power systems rely on ancillary services (ASs) to ensure system security and stability. Until recently, only the conventional power generation resources connected to the transmission grids were allowed to provide these ASs managed by the transmission system operators (TSOs), while distribution system operators (DSOs) had a more passive role, focused on guaranteeing distribution capacity to bring power to final consumers with enough quality. Now, with the decarbonization, digitalization and decentralization processes of the electrical networks, the growing integration of distributed energy resources (DERs) in distribution grids are displacing conventional generation and increasing the complexity of distribution networks’ operation, requiring the implementation of new active and coordinated management strategies between TSOs and DSOs. In this context, DERs are becoming potential new sources of flexibility for both TSOs and DSOs in helping to manage the power system. This paper proposes a systematic characterization of both traditional and potentially new ASs for TSOs, and newly expected DSO local system services to support the new distribution grid operation paradigm, reviewing, in addition, the main TSO-DSO coordination mechanisms.
Highlights
Ancillary services (ASs) are grid services needed to support the transmission of electric power from the generators to the consumers at the distribution grids, to guarantee the continuity, quality and security of the supply
This paper presents a practical review of the existing and potential new ASs for transmission system operators (TSOs) and new local system services for distribution system operators (DSOs), with an emphasis on DSO services that will help to address the new operation paradigm of the distribution grids
It summarizes the main TSO-DSO coordination mechanisms and flexibility markets organizations proposed in the literature to acquire this flexibility
Summary
Ancillary services (ASs) are grid services needed to support the transmission of electric power from the generators to the consumers at the distribution grids, to guarantee the continuity, quality and security of the supply. Many research works and conceptual and commercial initiatives have been proposed in recent projects Their main objectives are improving DER integration as active FPs in local system services to support the distribution grids’ operation, and, under TSO-DSO coordination schemes, contributing to the transmission grid operation through the DER participation in system-wide services. Based on existing literature and on the work of the previously mentioned projects (namely EU-SysFlex, Interconnect and EUniversal), this paper presents a characterization of current and expected TSO and DSO flexibility needs in the current decarbonization context, and the services that DER can provide to meet those needs. One of the motivations for this work was the fact that previous approaches did not provide such a formal, comprehensive and consistent review and vision on both TSO and DSO grid services, with a special focus on DSO services and on the flexibility markets structures for their acquisition.
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