Investigation of modular multilevel converter control methods

Ertürk, Feyzullah
The thesis focuses on the analysis and control of modular multilevel converter (MMC). The control structures used in the control of MMC are presented. Outer control loops of the converter such as output current, DC-link voltage, and power controls as well as inner control structures unique to the converter such as circulating current control and sorting algorithm based submodule voltage balancing are investigated. In addition, switching methods proposed for MMC are also described. These control and switching methods are examined on a sample DC/AC MMC and their effects are evaluated. In addition, parameters such as circulating current control, sorting algorithm based submodule voltage balancing, modulation methods, used in MMC control, as well as power factor are evaluated on their effects over semiconductor power loss in the system via detailed analysis. Total system loss and individual semiconductor loss are dwelled on. Later, the applicability in HVDC is inspected on a sample back-to-back MMC system and a method to improve dynamic operation is proposed. After the shortcomings of MMC in low-frequency operation are described, the control method that allows MMC to be used in motor drive application is explained and applied in a sample system via simulation. The study is realized by mathematical analysis, topological design, controller design and detailed computer simulation.


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Citation Formats
F. Ertürk, “Investigation of modular multilevel converter control methods,” M.S. - Master of Science, Middle East Technical University, 2015.