Coordinated Load Flow Solution for Coupled Transmission-Distribution System Incorporating Load Modeling

Abstract

With the flow of time there is a rapid addition of distributed generation (DG) units in the distribution system (DS). This transformation of DS from passive to active network has made the examination of coupling between transmission and distribution (T&D) systems more significant. Conventionally, the load flow studies are performed individually for both transmission system (TS) and DS, presuming the other system as an equivalent. But to achieve a global solution for the entire power system, a Coordinated Load Flow (CLF) method is required. It will perform load flow in a distributed manner with a little reciprocity of information at the common bus, in order to reduce the computational complexities of solving large scale problems. This will allow to analyze the impact of detailed modeling of DS on global load flow solution which was otherwise neglected in traditional methods. This paper firstly presents the methodology to perform CLF. Further, the significance of CLF method is proved especially in the presence of voltage dependent loads in DS and its performance is compared with the solutions of independent T&D load flows. Numerical simulations are performed on various test cases and the results are validated using Newton-Raphson load flow method with optimal multiplier.