A promising configuration for future smart grids is an AC/DC hybrid topology that enables the integration of AC/DC energy resources and modern loads, thus permitting the consequent formation of AC/DC hybrid microgrids (HMGs). An understanding of AC/DC HMGs and their operational premise during islanding will certainly pave the way toward the realization of a future smart grid that includes a plug-and-play feature. However, the planning and operation of such isolated and hybrid systems are reliant on a powerful and efficient power flow tool. To this end, this paper proposes a novel unified, generic, and flexible power flow algorithm for isolated AC/DC HMGs. The power flow subproblems related to AC and DC subgrids are described mathematically by a set of linear and nonlinear equations and are solved simultaneously using a Newton trust-region method. The proposed algorithm is generic in the sense that it includes consideration of the unique characteristics of islanded AC/DC HMGs: a variety of possible topologies, droop controllability of the distributed resources (DRs), and bidirectionality of the power flow in the interlinking converters (ICs). The new power flow formulation is flexible and permits the easy incorporation of any changes in DR operating modes and IC control strategies. The developed algorithm was tested and applied for analyzing selected operational and control aspects of isolated AC/DC HMGs, including inaccurate power sharing and interlinking converters characterized by differing control strategies. The proposed load flow program can form the basis of and provide direction for further studies of isolated AC/DC HMGs. |
