A steady-state analysis tool for unbalanced islanded hybrid AC/DC microgrids

This paper provides a novel power flow algorithm as a viable tool to accurately analyze the steady-state behavior of islanded hybrid ac/dc microgrids. The operational philosophy of these networks is sophisticated since both the ac frequency and dc voltage are variable, coupled, and sensitive to the control schemes of the distributed generators (DGs) and interlinking converters (ICs). In order to render the analysis generic, mathematical models are developed for control schemes of the DGs and ICs under unbalanced conditions. The presented models are then incorporated into an optimized power flow formulation and the solution is found using the globally convergent Newton-Trust Region (NTR) method. The algorithm accuracy is verified using detailed time-domain simulations in PSCAD/EMTDC environment. The effectiveness of the introduced power flow algorithm is illustrated via two case studies. The first case investigates parallel operation of droop-controlled ICs and highlights the effects of IC settings on load sharing among subgrids and power-transfer sharing through installed ICs. The second case reveals the significance of analyzing the loading condition for each phase of the DGs rather than for the total three-phase power generation, which is commonly followed in steady-state analysis in the reported literature.