Paul Frutos

Dynamic interactions among AC railway networks and train power converters have been reported to cause low-frequency oscillations (LFO) and eventually instability phenomena, which can collapse the railway power system. Several system parameters can influence the appearance of LFO, including catenary line length, power consumption, control bandwidths, etc. This paper proposes a methodology for the analysis and understanding of the impact of all these parameters on the LFO. The proposed method combines time-domain simulations with eigenvalue analysis. Eigenvalue migration will be shown to be a powerful tool to understand the risk of instability and to analyse potential remedial actions.

Dynamic interactions between AC railway electrification systems and traction unit power converters can result in low frequency oscillation (LFO) of the contact-line voltage amplitude, which can lead to a power outage of the traction substation and the shutdown of train traffic. Several system parameters can influence the low frequency stability of the railway traction power system, including contact-line length and traction unit parameters such as transformer leakage inductance, DC-link capacitance, control bandwidths and synchronization systems. This paper focuses on the influence of these parameters on the LFO. The methodology is based on a frequency-domain analysis. Nyquist and Bode diagrams are used to determine the stability limit. The validation of the method is performed through the use of time-domain simulations.

This paper reports on the development of an efficient C-script implementation of a 3D Space Vector Modulation (3D-SVM) algorithm for a Three Phase Four-Leg Voltage Source Inverter. The duty cycles calculations are performed in the three dimensional stationary frame $\alpha \beta \gamma $. The algorithm takes advantage of the finite-set of space-vectors in order to avoid calculating a matrix inversion. The algorithm is implemented in a C-script and tested by simulation in PLECS.

This paper presents a control performance comparison by simulation of a three and four-leg voltage source inverters for autonomous and grid connected operation under balanced and unbalanced loads; and asymmetrical voltage references. The voltage source inverters are described in the stationary frames αβ and αβ in order to perform the system control action by employing a proportional resonant current compensator. Results are obtained by simulations in PLECS, which demonstrate that the three and four leg converters can achieve similar results under balanced and unbalanced loads. Besides, the four-leg inverter is able to control asymmetrical current and voltage references.

In a solid state transformer (SST), one of the most important roles is played by the dc-dc converter interfacing the high voltage port and the low voltage port while providing galvanic isolation. This paper proposes a quad-active-bridge (QAB) converter as the basic cell of a Modular Multilevel Converter (MMC) based solid state transformer for the integration of distributed energy resources (DER) and distributed energy storage systems (DESS) into the grid. This study comprises power transfer analysis, modeling and control of the QAB for this application. Furthermore, this paper shows an alternative method based on the star-mesh transformation to built the multiwinding tranformer equivalent circuit, that relates any two ports of the multiple-active-bridge (MAB) converter through a link inductance, which allows to describe power flow. Results are obtained by simulations in PLECS.