Comparison of Two Cascaded Converter Topologies for Voltage Balancing in AC Railway Substations

Abstract

Due to the increase in rail traffic, the 25 kV/50 Hz single-phase substations can cause an unbalance in the phase voltages of the upstream three-phase network. This situation becomes unacceptable for the electricity transmission system operator and the implementation of an unbalance compensator is inevitable. In recent years, several power electronic solutions have been proposed. They are based on Power Electronic Building Blocks (PEBB) which can be connected in series or in parallel in order to achieve the required power level. They offer advantages in terms of modularity and implementation of low voltage power devices which thus improve the global system efficiency. In this paper, the authors present two modular topologies based on the principle of the Steinmetz load-balancing circuit. The first topology relies on cascaded AC choppers and the second one is based on cascaded H-bridge inverters. Analytical calculations and simulations allow a comparative analysis of these two topologies in terms of power semiconductor losses and stored energy in reactive devices.