Common-mode insertion indices compensation with capacitor voltages feedforward to suppress circulating current of MMCs

Xiaoling Xiong, Xiongfei Wang, Dong Liu, Frede Blaabjerg, Chengyong Zhao

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

In order to improve the efficiency of modular multilevel converters (MMCs) and reduce the capacitor voltage ripples, the circulating current between the phase-legs should be suppressed. In existing circulating current suppression control (CCSC) methods, multiple resonant regulators or dq-frame integrators are usually employed to reduce the harmonic components. Besides the complexity, it requires additional designs of controller parameters, which relies on accurate frequency and sequence information of the circulating currents. In this paper, a common-mode (CM) insertion indices compensation method is introduced to realize CCSC, which is based on feeding forward the capacitor voltages. This approach not only facilitates the analysis of circulating current mechanism with a deep insight, but also provides a simple approach to achieve a wide bandwidth circulating current suppression without considering the specific harmonic frequencies and sequences. The latter one makes it easy to be used even in the unbalanced, multi-frequency or variable fundamental frequency ac systems. In addition to these advantages, the proposed compensation method can maintain inter-arm capacitor voltages balanced without additional differential energy control loop, which is required in the existing capacitor voltage feedforward scheme. Analytical and extensive simulation results are given for validating the effectiveness of the proposed approach.
Original languageEnglish
JournalCPSS Transactions on Power Electronics and Applications
Volume5
Issue number2
Pages (from-to)103 - 113
Number of pages11
ISSN2475-742X
DOIs
Publication statusPublished - Jun 2020

Keywords

  • Capacitor voltages feedforward
  • circulating current suppression control
  • common-mode insertion indices
  • compensation method
  • Modular Multilevel Converter (MMC)

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