The challenges of estimating the impact of distributed energy resources flexibility on the TSO/DSO boundary node operating points

• Published in: Computers & operations research 2018-08, Vol.96, p.294-304
• Main Authors: Silva, João, Sumaili, Jean, Bessa, Ricardo J., Seca, Luís, Matos, Manuel, Miranda, Vladimiro
• Format: Article
• Language: English
• Subjects: Capacitor banks; Discrete variables; Distributed generation; Distribution networks; Economic forecasting; Electric power lines; Energy resources; Estimating techniques; Flexibility; Flexible assets; Operations research; Optimization; Power flow; Reactive power; Renewable energy sources; Straight lines; Studies; Tangent straight lines; Tap changers; Transmission networks; Uncertainty
• ISSN: 0305-0548; 1873-765X; 0305-0548
• DOI: 10.1016/j.cor.2017.06.004

•A new optimization model to estimate the active and reactive power flexibility ranges at the TSO/DSO boundary nodes.•An adaptive objective function based on a family of straight lines with different slopes allows exploring the flexibility area perimeter.•A clear increase in the flexibility area identification within less computational time comparing to a random sampling approach is obtained.•The existence of discrete variables may lead to the appearance of disjoint flexibility sub-areas.•An approach belonging to the decision-aid field that allows to increase the bidirectional exchange of information between TSO and DSO. The increasing penetration of renewable energy sources characterized by a high degree of variability and uncertainty is a complex challenge for network operators that are obligated to ensure their connection while keeping the quality and security of supply. In order to deal with this variable behavior and forecast uncertainty, the distribution networks are equipped with flexible distributed energy resources capable of adjusting their operating point to avoid technical issues (voltage problems, congestion, etc.). Within this paradigm, the flexibility that, in fact, can be provided by such resources, needs to be estimated/forecasted up to the transmission network node (primary substation) and requires new tools for TSO/DSO coordination. This paper addresses this topic by developing a methodology capable of finding the flexibility area while taking into account the technical grid constraints. The proposed approach is based on the formulation of a single optimization problem which is run several times, according with the expected precision for the flexibility area estimation. To each optimization problem run, a different objective function belonging to a family of straight lines is assigned. This allows exploring the active and reactive power flow limits at the TSO/DSO boundary nodes – which define the flexibility area. The effectiveness of the proposed model has been evaluated on two test networks and the results suggest a step forward in the TSO/DSO coordination field. Nevertheless, further investigations to study the effect of assets with discrete control nature (e.g., on load tap changers – OLTC, capacitor banks) on the occurrence of disjoint flexibility areas should be carried.