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JEET, Vol. 13, No. 6, November 2018
VPI-based Control Strategy for a Transformerless MMC-HVDC System Under Unbalanced Grid Conditions
Rae-Young Kim
Area B - Electric Machinery and Power Electronics
Abstract This paper introduces a control method for a transformerless MMC-HVDC system. The proposed method can effectively control the grid currents of the MMC-HVDC system under unbalanced grid conditions such as a single line-to-ground fault. The proposed method controls the currents of the positive sequence component and the negative sequence component without separating algorithms. Therefore, complicated calculations for extracting the positive sequence and the negative sequence component are not required. In addition, a control method to regulate a zero sequence component current under unbalanced grid conditions in the transformerless MMC-HVDC system is also proposed. The validity of the proposed method is verified through PSCAD/EMTDC simulation.
Keyword Current control,High voltage direct current(HVDC) transmission system,Modular multi-level converter(MMC),Transformerless,Unbalanced grid,Vector proportional-integrator control.
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