Series Connection of Power Devices for Modular Multilevel Converter based High Voltage Direct Current Transmissions

As the electricity consumption continues to grow, the need for long distance bulk power transmission has increased significantly. Compared to traditional ac solutions, high voltage dc transmissions offer a number of advantages such as higher efficiency, lower cost, and smaller size. The high voltage dc transmission technologies have experienced a number of generations coupled with the development of power devices which form the backbone of the converter stations. The latest generation is based on voltage source converters enabled by fully controllable silicon devices that offer tremendous flexibility. However, the available voltage capacity of these devices has greatly limited the system voltage levels, which then limits the transmission capacity and efficiency. To address these issues, this project will develop a series connection mechanism featured by almost zero loss and simple self-balancing and synchronization algorithm, as well as its implementation in modular multilevel converter based high voltage dc transmission systems. The developed techniques can potentially transform many other high power electronics applications such as power supplies for medical equipment, industrial motor drives, and pulsed power supplies for fusion power reactors. These applications will impact various aspects of the society and promote the usage of clean and green energy. The proposed project is intrinsically comprehensive involving different facets of power engineering ranging from device, circuit, to system level research, which will provide unique and high quality training for the next generation students and engineers. The proposed educational activities will also broaden the participation of women and other under-represented groups. The objectives of this project are to develop a novel series power device connection technique and explore its implementation in modular multilevel converter with applications in high voltage dc transmissions. It addresses the most challenging issues in connecting power devices in series with a simple and reliable topology and voltage self-balancing algorithm. The application oriented study of the proposed project will generate critical knowledge regarding component sizing, trade-off and optimization study, and system level implementation. Moreover, series connection of silicon carbide devices will be evaluated. The multiple prototypes to be developed will provide engineering experience and guidelines for real implementation, verification of the theoretical analysis, and can be used as building blocks for circuit and system level prototypes. The series connection of power devices will advance the modular multilevel converter technology with increased voltage rating, reduced sub-module count, and reduced size of passive components. This project will transform the realization of modular multilevel converter based high voltage dc transmissions.