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Modular Multilevel Converters for Power System Applications

出版	Universitat Politècnica de Catalunya, 2017
URL	http://books.google.com.hk/books?id=7hwiygEACAAJ&hl=&source=gbs_api

註釋This thesis discusses the operation of the grid-tied modular multilevel converters (10C) applied on the dc power transmission, particularly on the medium and high-voltage applications. First, it is presented the evolution of the power converters used on the high-voltage dc transmission field (HVdc) with special focus on the modular multilevel-based power converters. Then, due to the intrinsic nature of the converter, besides the control requirements for its dc and ac buses interactions, its energy storage should be carefully managed in order to achieve a safe and knowledgeable operation of this power converter. Hence, its control requirements are presented and mathematically supported. Moreover, the progressive design and validation of its control loops is addressed in this thesis by means of the converter simulation over a broad range of operating conditions. One key-point factor of the 10C performance is the strategy followed to modulate the voltages generated on its arms. In this vision, different modulation techniques were combined with peculiar zero sequence signals in order to analyze their impact on the voltages across the converter arms and its intrinsic performance. This study was also complemented by different procedures followed to balance the energy storage of its capacitors. A transversal research question of this voltage source converter topology is its efficiency. Then, besides the analysis of the ac power flow impact on the power losses produced by its semiconductors, it is deduced and proposed a mathematical expression that that can describe the power losses produced semiconductors, over a broad range of operating conditions of the 10C. Finally, it is explored the possible degrees of freedom of an half-bridge-based 10C whenever it is operating in the static synchronous compensation (STATCOM) mode. Depending on the converter operation aspect that is required to be optimized, the voltage across its dc poles can be adjusted to achieve an improved performance of the 10C.