Space-Vector Versus Nearest-Level Pulse Width Modulation for Multilevel Converters

This paper studies the inherent relationship between two widely used pulse width modulation (PWM) methods for multilevel converters, i.e., the space vector modulation (SVM) method, also called space vector pulse width modulation, and the nearest-level modulation method. The nearest-level modulation method directly controls the voltage of each phase, while the SVM method simultaneously deals with all phases. It is demonstrated in this paper that the two modulation methods are functionally equivalent: with proper common-mode voltage injections, the nearest-level modulation method is equivalent to the SVM method; by selecting the appropriate redundant switching sequences and the corresponding duty cycles, the SVM method is equivalent to the nearest-level modulation method. Nevertheless, the SVM method can conveniently provide more flexibility of optimizing the switching patterns, without the need of designing sophisticated common-mode voltages. An efficient and flexible modulation method for any multiphase multilevel converter is, therefore, proposed, which combines the advantages of the nearest-level modulation and the SVM methods, i.e., both with less computational burden and high flexibility of optimizing the output waveforms. Simulation and experimental results validate the analysis.