Three-Leg Integrated Stage AC–DC Solid-State Transformer Feasible for MV Railway Applications

Abstract

This work proposes an extensive investigation of a solid-state transformer (SST) with an integrated ac–dc bidirectional stage feasible to medium-voltage (MV) railway systems, based on an arrangement that uses an input-series-output-parallel (ISOP) configuration with identical power modules. Each module has a three-leg configuration: in the primary side, there are two interleaved legs using coupled windings connected to a medium-frequency transformer (MFT) and another leg operating at the grid frequency; and a conventional H-bridge is used in the secondary side. Qualitative and quantitative analyses are presented to demonstrate the aspects of the proposed topology and are validated by steady-state experimental results using an 8.33-kW prototype. Dynamics results are also presented, with a two-module structure with a low rated power to validate the control strategy and modularity. A comparative analysis considering real traction system parameters is carried out, demonstrating some well-defined trends of the proposed topology in this application, such as a reduction in conduction loss up to 32% and lower number of switches compared with another five topologies. The analyses and preliminary results show that the proposed structure could indeed be considered as a possible solution for SSTs in MV traction systems.