A Generalized Model for Unified Ac-Dc Load Flow Analysis

The tendency to gain the benefits of both ac and dc grids pushed the power industries to introduce the ac-dc hybrid system as the future of distribution systems. Although these grids bring substantial advantages for the power system, such as stability, reliability, resiliency, they add more complexities to power network studies, such as load flow, short circuit, dynamic, stability analyses. These complexities arise due to the presence of ac-dc converters. In a hybrid grid, ac and dc system equations should be solved either simultaneously or sequentially. Despite the sequential method that was in a center of attention, the simultaneous approaches have not been deeply researched due to some technical barriers. This paper aims to explore the ac equivalent circuits of dc grids so that the ac-dc hybrid grid can be considered and analyzed as one ac grid. Accordingly, dealing with separate sets of equations for ac and dc networks is avoided. Therefore, all of the classical power system studies, such as the Newton Raphson (NR) based load flow algorithm, stability and dynamic analyses, and short circuit study, can be applied to the ac-dc network with a small modification that substantially saves time and effort.