Space Vector Modulation in the 45° Coordinates α^′β^′ for Multilevel Converters

Space vector modulation (SVM) strategy is widely used in two-level and three-level converters because of its advantages. However, the sector triangles, switching states, and switching sequences increase dramatically as the number of levels increases, which makes it difficult to implement the SVM algorithm in industrial applications of high-voltage and high-power multilevel converters. To extend the SVM strategy to high-voltage and high-power converters, a new SVM algorithm is proposed in this article with the 45° coordinates α'β'. In the α'β' coordinates, based on the relationship between the phase voltage and the line voltage of a star-connected converter, the reference vectors calculated from phase-voltage reference signals are directly used as line-voltage reference vectors. Moreover, two line-voltage levels are used as two components of the space vector, with the sum of these two components being the third line-voltage level. These three components are directly used as the switching state signals of the control line voltages. The proposed method avoids the 2/3 conversion that must be completed in the conventional SVM algorithm and does not need to calculate redundant switching states. It greatly simplifies the SVM algorithm and ensures that the common-mode voltage of the converter is zero. Finally, the proposed algorithm is validated with extensive experimental results.