The Journal of Engineering (Jan 2019)

Hybrid-wave modulation for modular multilevel high-frequency DC converter in DC distribution application

  • Yu Wang,
  • Yuewu Wang,
  • Guidong Zhang,
  • Si-Zhe Chen,
  • Yun Zhang

DOI
https://doi.org/10.1049/joe.2018.8637

Abstract

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Compared with AC distribution networks, DC distribution networks reduce the utilisation of power converters, power loss, and construction cost. In DC distribution network, the high-frequency modular multilevel DC converter (MDCC), which connects the low-voltage DC link with medium- or high-voltage DC links, becomes a practical equipment to realise the bus connection, voltage conversion, and electrical isolation. Especially, high-frequency link (HFL) modulation plays an important role in converter performance. The square-wave (SW) modulation obtains better power transfer capability and higher DC voltage utilisation. However, the SW modulation leads to a large dv/dt stress upon HFL transformer. The sinusoidal, triangle and quasi-square-wave (QSW) modulations reduce dv/dt and harmonics significantly. However, the power transfer capability and DC voltage utilisation are also reduced. To address dv/dt stress problem, ensure high DC-voltage utilisation and maintain a strong power transfer capability simultaneously, a hybrid-wave modulation strategy, which composed of QSW and SW modulation, is proposed for MDCC. The experimental results verify the analysis and proposed scheme.

Keywords