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Mathematical Problems in Engineering
Volume 2016, Article ID 2968484, 6 pages
Research Article

Voltage Balancing Method on Expert System for 51-Level MMC in High Voltage Direct Current Transmission

1School of Energy Science and Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
2The Centre of Energy, The University of Adelaide, Adelaide, SA 5005, Australia

Received 6 September 2015; Revised 2 March 2016; Accepted 28 March 2016

Academic Editor: Tarek Ahmed-Ali

Copyright © 2016 Yong Chen and Xu Zhang. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The Modular Multilevel Converters (MMC) have been a spotlight for the high voltage and high power transmission systems. In the VSC-HVDC (High Voltage Direct Current based on Voltage Source Converter) transmission system, the energy of DC link is stored in the distributed capacitors, and the difference of capacitors in parameters and charge rates causes capacitor voltage balance which affects the safety and stability of HVDC system. A method of MMC based on the expert system for reducing the frequency of the submodules (SMs) of the IGBT switching frequency is proposed. Firstly, MMC with 51 levels for HVDC is designed. Secondly, the nearest level control (NLC) for 51-level MMC is introduced. Thirdly, a modified capacitor voltage balancing method based on expert system for MMC-based HVDC transmission system is proposed. Finally, a simulation platform for 51-level Modular Multilevel Converter is constructed by using MATLAB/SIMULINK. The results indicate that the strategy proposed reduces the switching frequency on the premise of keeping submodule voltage basically identical, which greatly reduces the power losses for MMC-HVDC system.