Modified Current Injection Method for Power Flow Analysis in Heavy-Meshed DC Railway Networks With Nonreversible Substations

Abstract

This paper proposes a Modified Current Injection method for power flow analysis, bespoke for the specific features of dc traction networks. It introduces major contributions when compared with the state-of the-art solution. In addition to simulating the nonlinear and nonsmooth behavior of the trains, the proposed algorithm can simulate reversible IGBT-based and nonreversible diode-based substations present in the system. These latter substations are the most common type and they supply unidirectional power flow from the ac distribution network to the dc traction subsystem. Depending on the voltage level at the dc side, the substations will be either blocked or conducting. This nonlinear behavior increases significantly the system complexity. Another key aspect of the proposed method is that it is also valid for heavily meshed networks. Even when the dc systems are usually radial or weakly meshed, the connections between the dc and the ac systems create multiple meshes, increasing the network topological complexity. In order to validate the performance of the proposed solution, the behavior of the algorithm is compared with the conventional derivative-based Trust Region Dogleg and the backward/forward sweep algorithm. This comparison shows convergence and speed improvements in the performance of the proposed algorithm.