Modular multilevel converter based high voltage direct current transmission system

The modular multilevel converter is a trending topology for voltage source converters of high voltage direct current transmission that makes it possible bulky electrical energy transfer over very long distances. In this work, an MMC based VSC-HVDC transmission system was designed, modeled, and simulated for balanced 3-phase operation. The time-domain simulations were based on semiconductor level switching. The MMC-HVDC transmission system was considered between two huge big generation centers to provide a control of DC power flow from one center to another. At the same time, reactive power or AC voltage at the terminals of each MMC station was also regulated for stable operation. MMC was designed using five half-bridges at each arm. So there exists 60 semiconductor IGBT switches for one MMC. A reliable modulation technique for the switching of IGBT switches has also been decided and verified in this thesis. The dynamic responses of the controllers of the MMC based VSC-HVDC transmission system have also been analyzed and verified in this work.