A Newton‐Raphson ‐based unified load flow of grid‐connected and islanded AC–DC microgrids

Abstract

The existing Newton-Raphson (NR)-based load flow for AC–DC microgrids (MG) implements a decoupled approach where the AC and DC sub-systems are modeled using separate variable sets. Therefore, such types of approach are not genuinely unified in nature. Here, in this article, we have attempted to formulate an NR-based load flow for AC–DC MG based on single set of variables. The approach has been developed by transforming the whole AC–DC system in terms of AC variables alone, which involves the conversion of DC lines and buses into their respective AC equivalent. At the same time, the proposed transformation concept eliminates the problem related to application of NR-based load flow with DC lines having their R/X ratio as infinity. Thus, a single Jacobian is sufficient enough to obtain the load flow solution. The proposed method applies to the grid-connected mode and also to the islanded mode of operation by considering the absence of slack bus. The proposed technique has been verified against existing results obtained using other methods and proves itself competent and accurate. The method further has been formulated for an unbalanced three-phase AC–DC network.