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Design principle of flexible protected controller for modular multilevel converter under unbalanced grid conditions
Author(s) -
Zhu Minglin,
Li Guojie
Publication year - 2018
Publication title -
ieej transactions on electrical and electronic engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.254
H-Index - 30
eISSN - 1931-4981
pISSN - 1931-4973
DOI - 10.1002/tee.22602
Subject(s) - modular design , controller (irrigation) , control theory (sociology) , grid , matlab , ripple , capacitor , voltage , three phase , weighting , engineering , computer science , electronic engineering , electrical engineering , control (management) , mathematics , physics , geometry , artificial intelligence , agronomy , biology , operating system , acoustics
In the grid‐connected modular multilevel converter (MMC) system, AC grid faults not only cause current imbalance and distortion which may lead MMC shutdown but also bring imbalance issues to the circulating currents and the module capacitor voltages. In this paper, a flexible protected control method employed in the dual d–q coordinates is presented. A weighting factor is introduced in the AC current controller to flexibly adjust the positive‐ and negative‐sequence components. The mathematical models of the converter based on the Kirchhoff law and the energy balance equations are investigated. Considering the system requirements such as the allowed maximum AC current and the allowed maximum capacitor voltage ripple in phase unit, the design principle of the flexible controller is proposed. Finally, the simulation results from MATLAB/Simulink as well as experimental results from a scaled‐down MMC prototype are presented to verify the theoretical analysis. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.