A sequential power flow algorithm for islanded hybrid AC/DC microgrids

This paper proposes a sequential power flow algorithm for hybrid ac/dc microgrids operating in the islanded mode. Unlike in grid-connected systems, variable, rather than fixed, frequency and voltage are utilized for power coordination between the ac and dc microgrids, respectively. The main challenge is to solve the power flow problem in hybrid microgrids while considering the absence of a slack bus and the coupling between the frequency and dc voltage. In the proposed algorithm, the ac power flow is solved using the Newton-Raphson (NR) method, thereby updating the ac variables and accordingly utilizing these variables in a proposed interlinking converter model for the dc problem. This sequential algorithm is iterated until convergence. The proposed algorithm is generic and can include different operational modes not only for the distributed generation units (DGs), but also for the interlinking converters. Detailed time-domain simulations using PSCAD/EMTDC have validated the algorithm's accuracy. Its robustness and computational cost are contrasted to those of conventional algorithms.