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.
In this paper, a modelling method of a 25 kV-50 Hz railway line, in a frequency range from 0 to 5 kHz, is presented. A model is proposed to quantify current and voltage harmonics generated by traction converters in different points of the network. An equivalent circuit, taking into account the skin effect for time-domain simulations, is also proposed. A new model, based on state space representation and transfer functions is developed to simplify the study of the interactions between several trains circulating on a line sector. As an example, the amplitudes of the harmonics generated by on-board active rectifiers are computed at several points of the network for a given topology of the overhead line and several positions of two trains on a sector with a junction.
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.
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