Multilevel converters: Topologies, modulation and control

This chapter has introduced the main multilevel converter topologies, i.e. the DCC, the FC, and the CHB converters, as well as the MMC, which is a recent topology that is expected to be widely applied in HVDC transmission systems. After classifying the modulation techniques, the basics of SVM and CB-PWM for multilevel converters have been presented. In the case of SVM, a modulation algorithm prone to be implemented in a digital processor has been applied to the three-level DCC (or NPC converter) and described in detail. A capacitor voltage balancing strategy based on selecting proper redundant vectors has also been embedded in the modulation. In the case of implementing a CB-PWM, several carrier signals are required for multilevel converters. Different carrier dispositions have been shown, including PS-PWM and LS-PWM. CB-PWM is especially interesting for modular converter topologies, such as the CHB converter and the MMC.