Journal of Power Electronics

The Korean Institute of Power Electronics (전력전자학회)
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Modeling, Analysis, and Enhanced Control of Modular Multilevel Converters with Asymmetric Arm Impedance for HVDC Applications

  • Dong, Peng (Wind Power Research Center, School of Electronic Information and Electrical Engineering, Shanghai Jiao Tong University) ;
  • Lyu, Jing (Wind Power Research Center, School of Electronic Information and Electrical Engineering, Shanghai Jiao Tong University) ;
  • Cai, Xu (Wind Power Research Center, School of Electronic Information and Electrical Engineering, Shanghai Jiao Tong University)
  • Received : 2018.07.06
  • Accepted : 2018.09.06
  • Published : 2018.11.20
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Abstract

Under the conventional control strategy, the asymmetry of arm impedances may result in the poor operating performance of modular multilevel converters (MMCs). For example, fundamental frequency oscillation and double frequency components may occur in the dc and ac sides, respectively; and submodule (SM) capacitor voltages among the arms may not be balanced. This study presents an enhanced control strategy to deal with these problems. A mathematical model of an MMC with asymmetric arm impedance is first established. The causes for the above phenomena are analyzed on the basis of the model. Subsequently, an enhanced current control with five integrated proportional integral resonant regulators is designed to protect the ac and dc terminal behavior of converters from asymmetric arm impedances. Furthermore, an enhanced capacitor voltage control is designed to balance the capacitor voltage among the arms with high efficiency and to decouple the ac side control, dc side control, and capacitor voltage balance control among the arms. The accuracy of the theoretical analysis and the effectiveness of the proposed enhanced control strategy are verified through simulation and experimental results.

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References

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