Advanced Modulation Techniques for Four-Leg Multilevel Converters: High Performance Converters for Distribution Systems

Throughout this work, the reader will find a comprehensive review and discussion about the state of the art and future perspectives of power electronics converters implemented in four-wire applications. The three-dimensional Space Vector Modulation (SVM) problem for this kind of converters is extensively discussed and a simple modulation algorithm for a three-level four-leg NPC converter is proposed and successfully validated in an experimental rig. Furthermore, additional issues barely reported in the literature for the four-leg NPC converter, such as: design of different switching patterns, the capability for balancing the voltages on the dc-link capacitors under unbalanced and non-linear loads, the overmodulation problem in a three-dimensional space and study of the switching frequency of the devices of the converter under modulation of non-sinusoidal and non-balanced voltages, are widely discussed. Afterwards, the proposed modulation technique is implemented in an aerospace application as a 400Hz, 110Vrms phase-to-neutral voltages, Ground Power Unit (GPU) under non-lineal and unbalanced loads.

Dr.-Ing. Félix Rojas obtained his doctoral degree from the Technical University of Munich, Germany in the field Power Electronics. He has worked in projects related to active filters for railway industry, Matrix Converters and Multilevel converters for distribution systems. Currently he is full time lecturer at the University of Santiago, Chile.