Nomenclature Overview and Beat Frequency in the Family of AC/AC Modular Multilevel Cascade Converters (MMCC)

The family of modular multilevel cascade converter (MMCC) has gained significant attention owing to its modular configuration, scalability, and superior harmonic performance. nearest-level control (NLC) not only leverages MMCC modularity but also minimize switching losses, making it highly effective for high-frequency operation. Nevertheless, applying NLC in the AC/AC MMCC configurations results in beat frequency oscillations, evident as coupled-frequency sidebands in the output voltage spectrum. This paper extends MMCC family nomenclature to include the emerging modular and multilevel topologies. Using the MMCC-triple star bridge cell (TSBC) topology, this study systematically investigates the beat frequency oscillations, introduces a double coordinate analysis and implements decoupled control loops. Our research presents a theoretical understanding and practical mitigation of beat frequency distortion. Simulation results validate the effectiveness of the proposed decoupled NLC, demonstrating its potential to enhance power quality in applications such as solid-state transformers (SSTs).     «

The family of modular multilevel cascade converter (MMCC) has gained significant attention owing to its modular configuration, scalability, and superior harmonic performance. nearest-level control (NLC) not only leverages MMCC modularity but also minimize switching losses, making it highly effective for high-frequency operation. Nevertheless, applying NLC in the AC/AC MMCC configurations results in beat frequency oscillations, evident as coupled-frequency sidebands in the output voltage spectrum...     »