A Full-Level Modulation Strategy for Half Bridge-Full Bridge Hybrid MMC in DC Distribution Grids

Guihong ZHANG; Chen WANG; Xiangcheng ZHANG; Shibin WANG; Zuoxia BAI; Zhongfeng ZHANG

doi:10.12204/j.issn.1000-7229.2022.06.008

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Electric Power Construction ›› 2022, Vol. 43 ›› Issue (6) : 75-83. DOI: 10.12204/j.issn.1000-7229.2022.06.008

Core Equipment of DC Power Grid ?Hosted by Associate Professor SONG Qiang, Associate Professor YU Zhanqing and Associate Professor ZHAO Biao?

A Full-Level Modulation Strategy for Half Bridge-Full Bridge Hybrid MMC in DC Distribution Grids

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Abstract

In order to improve the operating performance of half bridge - full bridge hybrid modular multi-level converter (MMC) with small quantities of submodules and promote its application in medium and low voltage fields such as DC distribution grids, a novel full-level modulation (FLM) strategy is proposed in this paper. The full-level output capability of full-bridge submodule (FBSM) is utilized in the proposed FLM, where a selected FBSM in arm operates in the “PWM mode”. The obtained full-level PWM wave is superimposed with the original step wave to further approximate the sine modulation wave. The operating mode of submodules is determined by the voltage sorting result, and at any time, there are two FBSMs in the phase unit operating in the “PWM mode”, outputting complementary full-level PWM waves. The results of simulation based on Matlab/Simulink and physical experiment reveal that the quality of voltage and current on AC side under FLM is much higher than that of the conventional nearest level modulation strategy. Compared with the carrier phase-shifted pulse width modulation, FLM performs better in terms of operating loss, control complexity and circulating current, which can satisfy the modulation requirements of medium and low voltage fields.

Key words

half bridge - full bridge hybrid MMC / small quantities of submodules / DC distribution grids / full-level modulation strategy

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Guihong ZHANG , Chen WANG , Xiangcheng ZHANG , et al . A Full-Level Modulation Strategy for Half Bridge-Full Bridge Hybrid MMC in DC Distribution Grids[J]. Electric Power Construction. 2022, 43(6): 75-83 https://doi.org/10.12204/j.issn.1000-7229.2022.06.008

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