DSO-TSO coordination and distribution network congestion management

Student thesis: Doctoral Thesis

Abstract

Flexibility from distributed energy resources (DERs) such as electric vehicles (EVs), solar photovoltaics, wind generators and battery storage, has the potential to significantly reduce the network reinforcement and operating costs required for the decarbonisation of the electricity system. New tools are required by the transmission system operator (TSO) and distribution system operator (DSO) to coordinate access to DER flexibility while maintaining stable system operation. According to the 2019 TSO-DSO report by the associations representing European distribution and transmission system operators ‘DSOs and TSOs need to co-ordinate closely for the use of flexibility to fulfil their missions as defined in regulation’. New coordination models have been proposed in academia as part the European Union SmartNet project, and a world-first regional reactive power market for DERs has been demonstrated in the South East of England in the ‘Power Potential’ project. With this in mind, this thesis aims to answer the following research questions: 1. How can access to distributed flexibility be coordinated between the DSO and TSO for system balancing and distribution system congestion management? 2. How can distribution system congestion management be scaled and coordinated with the TSO for millions of flexibility providers down to LV level? To investigate these problems, novel DSO-TSO coordination schemes, under Local and Decentralised market frameworks, have been developed and demonstrated on a distribution system with high DER penetrations. In the Local market, DERs are cleared by the DSO to participate directly in the TSO market, whereas in the Decentralised market, the DSO aggregates DER flexibility to the Transmission-Distribution interface for participation in the TSO market. Case studies have been investigated on the performance of the DSO-TSO coordination schemes, and it has been concluded that the Local market provides the most promising coordination mechanism in terms of complexity, tractability, and compatibility with the existing TSO balancing market operation of Great Britain. By operating multiple DSO regions in parallel, the Local market has been demonstrated to offer a more scalable solution than a single centralised network model. In the cases studied, it was observed that the requirements of the DSO and TSO generally aligned, however, when this was not the case in the Local market, the DSO is given priority access to DERs to solve distribution level constraints and any remaining flexibility is made available to the TSO. The DSO-TSO coordination schemes developed in this thesis solve congestion on balanced medium/high voltage networks using optimal power flow (OPF) techniques in a GB ‘balancing’ style market operating close to gate closure (1-2 hours ahead of delivery). However, this solution is not considered suitable for application to the millions of domestic customers connected at low voltage (LV). This is because it assumes balanced phases whereas LV networks are often unbalanced and existing three-phase OPF techniques for unbalanced networks may require too much computational overhead (processing power and time). Scalable three-phase LV congestion management solutions are required to minimise the amount of network reinforcement required to facilitate the electrification of heat and transport. In this thesis, a novel and scalable LV congestion management scheme (CMS) has been developed and integrated with the Local market DSO-TSO coordination scheme to provide the DSO and TSO access to EV flexibility located at household level while respecting LV network constraints. By applying the CMS to a set of LV networks, it is found that the hosting capacity for EVs can be more than doubled compared to uncoordinated EV charging. The LV CMS represents a key research output from the work of this thesis. It provides a way to access distributed flexibility located at LV in a coordinated way such that the DSO and TSO can achieve system balancing and incorporate distribution system congestion management while addressing the scalability issues.
Date of Award14 Mar 2022
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council) & University of Strathclyde
SupervisorStuart Galloway (Supervisor)

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