Cascaded H-Bridge and Modular Multilevel Converters: A Review

This chapter provides an in-depth exploration of multilevel converter technologies, specifically focusing on the cascade H-bridge multilevel inverter (CHBMLI) and modular multilevel converter (MMC), which are crucial for medium-voltage high-power drives. The CHBMLI is examined in detail, covering its symmetrical and asymmetrical operation modes, comparisons with basic multilevel inverters (MLIs) such as DCMLI and FCMLI, and various pulse width modulation (PWM) techniques. Additionally, its applications in grid integration, FACTS, and motor drives are discussed. The chapter also delves into the MMC, discussing its evolution from basic MLIs, addressing isolated DC sources, capacitor unbalancing, and harmonic profiles. The basic structure of MMC, comprising half-bridge and full-bridge cells, is explained, along with mathematical modeling of energy exchange between arms and phases. Various circuit configurations, including AC-DC, DC-AC, three-phase to one-phase, three-phase to three-phase, three-phase to multiphase, and DC-DC converters, are explored, as well as fault analysis and PWM techniques for balancing capacitor voltage across individual cells. Finally, the significance of MMC in diverse applications is examined, highlighting its importance in medium-voltage high-power drives.