SPACE VECTOR MODULATION FOR ASYMMETRICAL CASCADED MULTILEVEL CONVERTERS

This paper describes a new Space Vector modulation (SVM) strategy for asymmetrical cascaded multilevel converters. A seven-level asymmetrical multilevel cascaded converter is considered. The modulation is carried out in a new coordinate system and is divided into two steps. First, the nearest switching-state vector to the reference vector is chosen for the high-voltage-low-frequency cells, and the synthesized voltage vector is subtracted from the reference, resulting in the reference for the low-voltage-high-frequency cells. Afterwards, the three-nearest low-voltage switching-state vectors are selected, and, for each sector of the SV diagram, a switching sequence is defined, aiming, for instance, to minimize the number of commutations. Simulation results are given to validate the proposed method, which is compared to the phase-shift and phase disposition carrier-based approaches, showing its superior performance.