Optimal Power Flow in AC/DC Microgrids With Enhanced Interlinking Converter Modeling

In this article, we propose an optimal power flow (OPF) paradigm for hybrid ac/dc microgrids. A meticulous model of the interlinking converter (IC) is developed and integrated into the OPF problem formulation. The resulting formulation is capable of solving the OPF of ac and dc subgrids in their standalone operations. A computationally efficient parabolic relaxation method transforms the nonconvex OPF model into a convex quadratic-constrained quadratic programming form. A sequential penalization method is applied to the relaxed OPF to achieve feasible solutions for the original formulation. The developed OPF formulation is tested on multiple modified 5-, 14-, 30-, 24-, 118-bus test systems, and a significant reduction in computational time is achieved in comparison with semidefinite programming relaxation. For a sequential penalized ac/dc OPF, the optimal values of both relaxations have a maximum difference of 0.025% for a 5-bus system. Finally, the modified IEEE 14-bus system is emulated in a real-time controller/hardware-in-the-loop setup to validate the proposed framework with continuously varying loads and IC switching status.