AC-OPF for Droop-Based Islanded Microgrids With Voltage- and Frequency-Dependent Loads

The variability of active and reactive power in electric loads, influenced by voltage and frequency fluctuations, presents significant challenges in the AC optimal power flow (AC-OPF) of islanded microgrids (IMGs). These fluctuations affect power demand, which, in turn, impacts system voltage and frequency, creating a complex interdependence that must be carefully addressed in the AC-OPF formulation. To tackle this issue, this study proposes a novel mixed-integer nonlinear programming (MINLP) model for AC-OPF in droop-based IMGs, incorporating voltage- and frequency-dependent loads (VFDL) while considering various technical constraints. To enhance computational efficiency and ensure solution optimality, the MINLP problem is transformed into a mixed-integer linear programming model through linearization techniques and approximations, making it solvable with commercial optimization solvers. The proposed model is implemented in the open-source Pyomo optimization framework and solved using Gurobi. The effectiveness of the proposed model is validated on an enhanced IEEE 33-bus benchmark system. The results indicate that including VFDLs significantly influences system operation, particularly in cost minimization and voltage profile.