Power circle diagrams and aggregate flexibility curves for active distribution networks

Abstract

The circular geometry of nonlinear power flow equations has conventionally been exploited as circle diagrams and capability curves for the steady-state analysis of the power network. Building upon such concepts and motivated by the need to analyze the power flow pattern due to resources in the distribution network, the flexibility of an individual bus to inject or draw apparent power in an active distribution network while maintaining the network’s static security is quantified in this paper. The power injection flexibility at multiple buses is aggregated at the bulk power delivery substation, i.e., the transmission-distribution interface bus. Flexibility aggregation is further subjected to the generation and storage capabilities of resources present in the distribution network. The circle diagrams are reported for the 33 bus active distribution network, while the aggregate flexibility curves are obtained for the modified 33 bus and 85 bus test networks using a continuation optimal power flow approach. These results, along with a comparison with a previous approach, indicate the practicality of the shapes of the aggregate flexibility curves for active distribution networks.