A Newton-Raphson-Based Sequential Power Flow Algorithm for Hybrid AC/DC Microgrids

A hybrid AC/DC microgrid (MG) has the advantages of both AC and DC subgrids, and the operator should perform an accurate power flow analysis to ensure the MG's operational economy and reliability. This paper proposes a Newton-Raphson-based sequential power flow algorithm for the hybrid AC/DC MG. First, the MG's islanded operation mode and the three-phase unbalance feature of AC subgrids are considered, and the droop control for distributed generations participating in the voltage and frequency regulation is modeled. Then, a sequential algorithmic framework is proposed to handle the coupling between AC and DC subgrids. Within this framework, the power flow of AC and DC subgrids is solved separately and iteratively with modified Newton-Raphson sub-algorithms. The accuracy of the proposed sequential algorithm is validated in comparison with the results from MATLAB/Simulink, and the advantage of employing this algorithm is confirmed compared with an equivalence approach. The case studies demonstrated that the proposed algorithm can significantly improve the result accuracy with acceptable computational time. Finally, the convergence performance of the proposed algorithm is verified in the cases of varying AC and DC subgrid loading.