Empirical Comparison of AC and DC Power Flow Models in Transmission Expansion Planning

Expansion planning models often rely on the DC power flow approximation for the sake of computational tractability. The AC power flow model, however, is the full representation of a power system's steady-state behavior, while DC power flow is a linear approximation, so it is important to understand how well the DC approximation performs in this context. In this paper, we investigate the impact of utilizing the nonlinear AC power flow model versus the DC power flow linearization in transmission expansion planning. We compare investment decisions obtained from the IDAES-GTEP package on a 5-bus and 9-bus test systems under several scenarios that vary line parameters, and initial results on a larger 123-bus network. Our results show that, for standard parameter ranges, AC and DC formulations yield similar expansion plans, whereas under extreme parameter variations that exaggerate losses or reactive effects the models can select different investment decisions, but with the AC formulation requiring substantially more computation time and similar final investment costs.