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Optimal suppression strategy for capacitor voltage ripples of hybrid MMCs under unbalanced grid voltages

Xu, Jianzhong, Wang, Junxin, Yang, Yukun, Wang, Jinan and Li, Gen 2022. Optimal suppression strategy for capacitor voltage ripples of hybrid MMCs under unbalanced grid voltages. IEEE Transactions on Power Delivery 10.1109/TPWRD.2022.3183065

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Abstract

Submodule (SM) capacitor voltage ripples in modular multilevel converters (MMCs) can be suppressed by harmonic injection strategy, which can reduce the volume and cost of MMCs. The existing methods using the dual harmonic injection strategy for hybrid MMCs only consider steady-state conditions. Harmonic injection strategies for unbalanced grid voltage conditions only use single harmonic injection and can be applied for single-phase faults. To address the above issues, this paper proposes an optimal dual harmonic injection of second-order harmonic current and third-order harmonic voltage strategy for hybrid MMCs. Firstly, the mathematical model of MMC under unbalanced grid voltages is established. Then the ripple characteristics of SM capacitor voltage are analyzed to reveal the relationship between the capacitor voltage and the arm power ripples. Based on the developed instantaneous arm power model, optimal harmonic injection parameters are calculated. A hybrid MMC simulation model is built in PSCAD/EMTDC to verify the effectiveness of the proposed strategy. The results show the excellent performance of the proposed strategy in suppressing the voltage ripples under unbalanced voltage conditions.

Item Type: Article
Date Type: Published Online
Status: In Press
Schools: Engineering
Publisher: Institute of Electrical and Electronics Engineers
ISSN: 0885-8977
Date of First Compliant Deposit: 16 June 2022
Date of Acceptance: 11 June 2022
Last Modified: 20 Jun 2022 22:22
URI: https://orca.cardiff.ac.uk/id/eprint/150538

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