Review of High Voltage DC/DC Modular Multilevel Converters

Smart grid has emerged as a solution to provide clean, reliable and efficient energy. Renewable energy resources, AC grid, load centers and distributed storage are the main components of a smart grid. High voltage DC (HVDC) transmission is emerging as an efficient system to connect these components to the smart grids as compared to high voltage AC (HVAC) due to less cost of transmission lines and low losses. High voltage AC/DC, DC/AC and DC/DC converters are the main constituents of the HVDC system to interconnect with the power generating systems, AC grid and load centers. Modular multilevel converter (MMC) possess features such as modular structure, scalability, reliability, fault tolerance and high step up/down ratios, which makes it an important topology for HVDC. Extensive research has been carried out on MMCs which has resulted in innovative circuit configurations of converters, novel modulation techniques and efficient control algorithms. This paper presents a review of different configurations of high voltage DC/DC MMCs, its operation and features. It also discusses the modulation and control techniques designed for DC/DC MMCs.