Optimal second-harmonic current injection for capacitor voltage fluctuation reduction in hybrid MMCs under grid-side SLG faults

Xu, Jianzhong, Deng, Weicheng, Li, Gen ORCID: https://orcid.org/0000-0002-0649-9493, Zhao, Chengyong and Chongru, Liu 2022. Optimal second-harmonic current injection for capacitor voltage fluctuation reduction in hybrid MMCs under grid-side SLG faults. IEEE Transactions on Power Delivery 37 (4) , pp. 2857-2866. 10.1109/TPWRD.2021.3118690

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Abstract

The second-harmonic injection strategy for modular multilevel converters (MMCs) can effectively suppress the capacitor voltage fluctuation in steady states. However, the capacitor voltage fluctuation under grid-side single-line-to-ground (SLG) faults will be more severe. Moreover, there is no research on the mitigation of capacitor voltage fluctuation under grid-side SLG faults for the hybrid MMC with mixed half-bridge and full-bridge sub-modules. To address this issue for hybrid MMCs, an optimal second-harmonic current injection scheme for mitigating the capacitor voltage fluctuation in the hybrid MMC under grid-side SLG faults is proposed in this paper. The mathematical models of arm power fluctuations of the hybrid MMC are firstly developed under both steady states and grid-side SLG faults. Then, the principle and optimal strategy of the proposed capacitor voltage fluctuation strategy are presented. The capacitor voltage fluctuation under grid-side SLG faults can be reduced by suppressing the three-phase arm power fluctuations. A hybrid MMC model with the proposed scheme has been established in PSCAD/EMTDC to verify its effectiveness and feasibility. Simulation results show that the average voltage fluctuation reduction rate can reach 55.77% with the proposed strategy.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Engineering
Publisher:	Institute of Electrical and Electronics Engineers
ISSN:	0885-8977
Date of First Compliant Deposit:	7 October 2021
Date of Acceptance:	5 October 2021
Last Modified:	07 Nov 2023 02:20
URI:	https://orca.cardiff.ac.uk/id/eprint/144743

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