Research on Power Flow Algorithm for Droop-controlled AC/DC Microgrid

With the proliferation of distributed energy resources, hybrid AC/DC microgrids have garnered significant attention due to their ability to efficiently integrate various power sources and loads. Among them, islanded microgrids employing droop control, which operate independently without reliance on the main grid, offer strong autonomy and represent a key future development direction. However, the power flow analysis for such systems differs fundamentally from that of traditional power grids: the system operates in an islanded mode without a slack bus, distributed generators utilize droop control, and the AC subsystem frequency is tightly coupled with the DC subsystem voltage through interlinking converters. These characteristics render traditional power flow algorithms based on a single slack bus inapplicable. The proposed algorithm addresses this by modeling the power transfer of the interlinking converters, quantifying the coupling relationship between the AC and DC networks as the interactive power at their point of connection. By iteratively updating this interactive power, the complex overall problem is decomposed into two independently solvable subproblems. For each subproblem, an improved forward-backward sweep method, which does not require derivative calculations, is applied to solve the power flow, taking into account the distinctive droop characteristics of each subgrid. Finally, simulation case studies verify the algorithm's accuracy and rapid convergence. This algorithm provides an effective analytical tool for the planning, operation, and control of such systems.