A Sequence Frame-Based Distributed Slack Bus Model for Energy Management of Active Distribution Networks

This paper proposes and develops a new distributed slack bus (DSB) model, in the sequence-components frame, for power-flow analysis of an islanded active distribution network (ADN) dominated by electronically coupled distributed energy resource (DER) units. The power-flow analysis distributes the system slack among several participating sources since, unlike the grid-connected systems, the reference bus DER unit is anticipated to have a limited power capacity. The main application of the DSB model is for a fast power-flow analysis of an islanded ADN to enable its real-time energy management and prevent DER capacity violation in between two consecutive optimal power-flow runs. Unlike the existing DSB models, the proposed model incorporates i) the participation of DER units with different control strategies (PQ and PV) in the system real and reactive slack compensation and ii) the DER power capacity limits. Based on a new definition of the "participating sources," the power-flow equations are augmented to incorporate the system real and reactive power slack as state variables. The proposed DSB formulation is incorporated in a sequence-frame power-flow solver (SFPS). Case studies are conducted to evaluate the impacts of adopting the proposed DSB model in the SFPS tool.