Advanced Modulation Techniques for Four-Leg Multilevel Converters

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.