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### Abstract

This paper presents a small-signal model for modular multilevel converters (MMCs) by using the harmonic state space (HSS) method. The ac output impedance of the MMC is then derived and compared with that of the commonly used two-level voltage-source converters (TL-VSCs). It turns out that the low frequency ac impedance of the MMC differs from that of the TL-VSC, due to the influences of internal dynamics, especially for the open-loop control and the voltage-mode control. In contrast, for the current-mode control, this difference can be minimized by the current regulator with a high-gain in the low frequency range. Moreover, despite the used control schemes, the high frequency ac impedance of the MMC is similar to that of the TL-VSC. The time-domain simulations are provided to validate the effectiveness of the theoretical analysis.

Original language | English |
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Title of host publication | Proceedings of the 2018 IEEE 19th Workshop on Control and Modeling for Power Electronics (COMPEL) |

Number of pages | 8 |

Publisher | IEEE Press |

Publication date | 10 Sep 2018 |

Pages | 1-8 |

Article number | 8459952 |

ISBN (Print) | 978-1-5386-5542-9 |

ISBN (Electronic) | 978-1-5386-5541-2 |

DOIs | |

Publication status | Published - 10 Sep 2018 |

Event | 19th IEEE Workshop on Control and Modeling for Power Electronics, COMPEL 2018 - Padova, Italy Duration: 25 Jun 2018 → 28 Jun 2018 |

### Conference

Conference | 19th IEEE Workshop on Control and Modeling for Power Electronics, COMPEL 2018 |
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Country | Italy |

City | Padova |

Period | 25/06/2018 → 28/06/2018 |

### Keywords

- modular multilevel converter
- small-signal model
- harmonic state space
- impedance modeling

## Fingerprint Dive into the research topics of 'AC Impedance Modeling of Modular Multilevel Converters and Two-Level Voltage-Source Converters: Similarities and Differences'. Together they form a unique fingerprint.

## Projects

- 1 Finished

## Multi-Timescale Stability of Modular Cascaded Power Electronic Systems

01/05/2017 → 30/04/2020

Project: Research

## Cite this

Wu, H., Wang, X., Kocewiak, L., & Harnefors, L. (2018). AC Impedance Modeling of Modular Multilevel Converters and Two-Level Voltage-Source Converters: Similarities and Differences. In

*Proceedings of the 2018 IEEE 19th Workshop on Control and Modeling for Power Electronics (COMPEL)*(pp. 1-8). [8459952] IEEE Press. https://doi.org/10.1109/COMPEL.2018.8459952