Unified load flow analysis for emerging distribution systems

This paper proposes a unified load flow analysis for transmission and distribution systems, based on the fast decoupled power flow method (FDPF). The method is centered on an extension of the conventional per unit normalization to circumvent the problems caused by low X/R ratio faced by distribution systems. The proposed extension establishes a complex voltampere basis. A properly definition of the base angle can adequate the X/R ratio of distribution systems as for instance the axis rotation previously presented in the technical literature. This paper also proposes a simple procedure that allows the utilization of different base angles for different parts of an interconnected system, so that conventional FDPF can be used to determine power flow solution of interconnected T&D systems in off line studies. Simulation results are conducted through IEEE standard test feeders, a south Brazilian distribution system and an interconnected T&D test system. Several operation conditions, including specific situations, such as closed ring operation of distribution systems, were simulated to evaluate the proposed approach.