Temperature-Dependent Unbalanced Three-Phase Optimal Power Flow Based on Alternating Optimizations

This article presents a method to solve an optimal power flow (OPF) problem for three-phase power systems, where the temperature of transmission line conductors is taken into consideration. The heat balance models of the overhead lines and the buried cables are included in the proposed OPF formulation. Transmission line admittance parameters depending on the conductor temperatures and the ambient temperatures are approximated from the precomputed data based on spline interpolations. The problem is then formulated as a constrained nonlinear optimization. An approximated solution based on the alternating optimization strategy is also proposed. In each iteration, the first optimization is performed by considering only bus voltage variables, while temperature variables are fixed. Then, the optimization is done for the temperature variables, while bus voltage variables are fixed. These steps are performed until the convergence conditions are satisfied. The numerical results on some test systems indicate that the proposed OPF approximation solution method can reduce the computational burden while providing satisfactory solutions.