Design and performance comparison of Two-level and Multilevel Converters for HVDC Applications

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Examensarbete för masterexamen
Master Thesis
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2011
Författare
Bonilla, Carlos Castillo
Tigga, Sweta Merilyn
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The purpose of this thesis is to compare a two-level and a multilevel converter for HVDC substation. For this study, both topologies were designed with different modulation strategies and compared on the basis of size, power losses and impact on power quality. The model of a basic substation was built in MATLAB, and a 450MVA converter was modeled for different topologies and modulation techniques. Further, the total losses of the converter were computed using different voltage/current ratings of the modules in order to derive a performance comparison. In addition to the evaluation of losses, the impact on the power quality was also analyzed for the multilevel converters. The results of the thesis revealed that, if harmonic emission without the need of external filters is the main criteria then, a twenty-three level converter with a modular structure could be used. The value of the output current THD in case of the twenty-three level converter is 0.52% which is well within the power quality standards and excludes the use of filters. The losses for a three level modular converter were found to be lower than the two-level converter (0.59% versus 1.14%). Also, the use of a 4.5kV module presented the lowest losses compared to other module ratings (2.5kV-6.5kV), for all converter topologies.
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Elkraftteknik, Electric power engineering
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