Efficient Space-Vector Modulation Algorithm for Multilevel Converters with Low Switching Frequencies in the Devices

This paper presents a novel space-vector modulation scheme that can be processed quickly by a digital-signal processor, in addition to achieving minimum switching frequencies in the devices of the converter. The modulation algorithm takes advantage of symmetry in the space-vector diagram to process all the calculations within the first sextant. An equivalent reference vector in this sextant is used for the calculation of duty cycles and the definition of optimal sequences of vectors. By simply interchanging the final states of the legs of the inverter of this equivalent vector generates the original reference vector in the corresponding sextant. The total number of switching steps in the final sequences is preserved; thus, optimal sequences of vectors need only be defined in the first sextant. This strategy is especially attractive for multilevel converters in which the total number of vectors and sequences is very high. Furthermore, since multilevel converters are usually applied to high-power systems, reducing the switching frequencies of the devices is an important goal. Efficiency of the modulation algorithm is verified in the three-level converter by simulation and experiment