A Modular Multilevel Converter With Self-Voltage Balancing Part II: Y-Matrix Modulation

In Part I of this paper, the self-voltage balancing nature of modular multilevel converters (MMCs) has been proven mathematically. To utilize this merit of MMCs, a novel modulation, namely Y-matrix modulation (YMM), is proposed to transform the math analysis of Part I into modulation practice. With the proposed YMM, MMCs have secured self-voltage balancing. Conventionally, either a complicated voltage balancing control, or extra components are embedded in MMCs to balance the capacitor voltage. Compared to conventional MMC capacitor voltage balancing strategies, YMM features simple algorithms and good reachability to high-level MMCs while maintaining the original half-bridge submodule topology. To simplify the analysis, YMM is introduced to two-level and three-level MMCs as examples. Then, the generalized YMM is derived, which is suitable for high-level MMCs. Several YMM based MMC case studies are provided for verification purposes.