Many works are dedicated to power electronic transformers in order to replace line frequency transformers. These new converters offer many degrees of freedom to the designer (switching frequency, magnetic material, rated voltage for switches. . . ). This paper presents a methodology to optimize the sizing of such power converters in order to compare different topologies for a given application. The proposed procedure maximises the efficiency of the converter under a limited volume. In this paper, the methodology is applied to compare different topologies of power electronic traction transformers (PETT) for railway applications. The considered case is a 2 MW converter supplied by a 25 kV-50 Hz catenary. The procedure is illustrated in simulation on a converter with 3.3 kV SiC switches. The best obtained efficiency is 98.9 % with 23 medium frequency transformers (MFT) of 28.6 L each.

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et al.. 25 kV-50 Hz railway power supply system emulation for power-hardware-in-the-loop testings.Abstract: This paper presents a methodology to consider the impedance of a grid in power hardware in the loop (PHIL) experiments to validate power converter control in presence of harmonics or resonances in the network impedance. As the phenomena to emulate are in a large frequency range, the skin effect in conductors has to be taken into account. A procedure is developed to model the network. Then, the model is simplified to reduce the computation requirements and discretised for real-time implementation. The proposed method has been applied to analyse the harmonic interactions due to on-board converters running on a 25 kV-50 Hz railway infrastructure for frequencies from 0 to 5 kHz. The model is computed in Matlab-Simulink, a SpeedGoat Performance Machine and a linear power supply are used for a real time implementation. The converter under test and the test bench are presented. Some experimental results are presented, showing the feasibility and the usefulness of the proposed approach.

This article proposes a methodology of Cost-Performance Assessment (CPA) enabling the efficient cost evaluation required for the Cost-Benefit Analysis (CBA). The proposed method is applied for the Modular Multilevel Converter (MMC) in offshore wind high voltage direct current (HVDC) transmission. Thanks to the developed model, an analysis of submodule voltage rating is performed demonstrating the interest of this methodology in the evaluation of new technologies for HVDC transmission. The analysis shows that increasing the submodule (SM) voltage could lead to savings in the MMC cost and weight.

Power electronic traction transformers (PETT) are multilevel AC/DC on-board converters, studied for railway applications to replace traditional solution with low frequency transformers. This paper focuses on the insulated DC/DC converter in a PETT. Three variants of resonant single active bridges (R-SAB) with 3-level NPC primaries are optimised to maximise the efficiency, under mass and dimension constraints. They are sized and compared for a 2 MW PETT on a 15 kV/16.7 Hz railway infrastructure, using 3.3 kV SiC MOSFETs and nanocrystalline C-core transformers with cast resin insulation and forced air cooling. The highest efficiency at nominal power, 99.17 %, is reached for a configuration with a 3-level full bridge NPC primary, a 2-level full bridge secondary, and a 32.1 L/49.1 kg transformer operating at 6 kHz.