Generalized Δ-Circuit Concept for Integration of Distributed Generators in Online Short-Circuit Calculations

In this paper, a novel concept of Generalized Δ-circuit is proposed, that enables integration of distributed generators (DGs) based on contemporary technologies into the short-circuit calculations of large-scale distribution systems. Modern DG models, such as doubly fed induction generators (DFIGs) and three-phase inverter based DGs (IBDGs) differ from the classical synchronous and induction generator models. It is shown that their models cannot be integrated in traditional short-circuit calculation procedures because they include a large number of possible fault current control strategies. Therefore, the concept of Generalized Δ-circuit is proposed and allows for any control strategy implemented in modern DGs to be integrated in the short-circuit calculation procedure. An improved backward/forward sweep procedure is developed for calculation of the Generalized Δ-circuit state. The faulted system state is calculated by the superposition of the known prefault state and calculated Generalized Δ-circuit state. Results show that unlike previously developed online short-circuit calculations, the proposed method can handle DFIGs and IBDGs with arbitrary selected fault current control strategies.