Unified Power Flow Algorithm for Standalone AC/DC Hybrid Microgrids

Recent studies on power flow analysis of islanded microgrids have become increasingly important and different solutions have been proposed. However, they are often limited to only ac or only dc microgrids and hence, the power flow must be solved separately. This paper proposes a straightforward and efficient method to solve power flows of hybrid ac/dc microgrids simultaneously, based on the well-established Newton-Raphson approach. It considers the lack of slack bus during islanded operation, the coupling of ac frequency and dc bus voltage, as well as the droop control of distributed generators. To achieve power sharing between the ac and dc subgrids, this method incorporates the interlinking converter droop constants in the equation. The algorithm was tested on modified hybrid microgrids involving multiple ac-dc subgrids. The results are compared against results from time-domain simulations to validate the algorithm's accuracy. The proposed technique can be easily implemented to aid the design and planning process of hybrid microgrids. © 2010-2012 IEEE.