Multilevel converter based on cascaded three-phase six-leg modules

Recently, modular multilevel converters (MMCs) and cascaded H-bridge (CHB) converters have been proposed to interface renewable energy sources (RESs) and energy storage systems (ESSs) with the grid. These converters address common drawbacks associated with two- and three-level voltage source inverters, such as limited voltage and current ratings, lack of modularity and scalability, and high harmonic content. However, MMCs and CHB converters often encounter challenges, including power oscillations, complex control strategies, and increased system complexity, particularly when galvanic isolation is required. This paper proposes a novel multilevel converter topology, the transformer-coupled cascaded six-leg bridge (TC[sbnd]CSLB) converter, designed to overcome these limitations. The TC[sbnd]CSLB topology comprises cascaded three-phase modules connected via separate insulating transformers, providing inherent galvanic isolation and modularity. The proposed converter achieves performance comparable to MMC and CHB topologies in terms of voltage levels, switch count, and power rating. Additionally, the use of three-phase modules minimizes power oscillations and simplifies control strategies. The inclusion of transformers—integral to the converter operation—facilitates the connection of the system to medium- and high-voltage grids, making the TC[sbnd]CSLB an ideal solution for applications where isolation and reliability are critical.