Evaluating the Over-Modulation Risk of Modular Multilevel Converters by Using Dynamic Modulation Ratio

Since the over-modulation can lead to the unstable operation of converters, the over-modulation risk evaluation is important in the circuit parameter selection, operating region design, and so forth. However, the wildly used evaluation method of modular multilevel converters (MMCs) comes from two-le...

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Bibliographic Details
Published in:IEEE journal of emerging and selected topics in power electronics 2022-12, Vol.10 (6), p.6705-6713
Main Authors: Liu, Zhijie, Li, Ke-Jun, Guo, Zhonglin, Wang, Jinyu, Qian, Jianhang
Format: Article
Language:English
Subjects:
Capacitors
Circuit design
Design parameters
Harmonic analysis
Insulated gate bipolar transistors
Modular multilevel converter (MMC)
Modulation
modulation ratio
Multilevel converters
over-modulation risk
parameter design
Power electronics
Risk assessment
steady-state analysis
Voltage
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Summary:Since the over-modulation can lead to the unstable operation of converters, the over-modulation risk evaluation is important in the circuit parameter selection, operating region design, and so forth. However, the wildly used evaluation method of modular multilevel converters (MMCs) comes from two-level converters; and the article found that its obtained result is not always accurate for MMCs because four assumptions will be introduced when the conventional modulation ratio (CMR) is used as the indicator. To solve the problem, a new concept, namely dynamic modulation ratio (DMR), is proposed. Comparing with the CMR, the DMR can dynamically change according to the variation of operating conditions and can reflect the modulation characteristics more accurately. Quantitative comparisons are carried out between the CMR-based and the DMR-based evaluation methods in various operating conditions. The comparisons show that the CMR-based method is only accurate under a few situations for MMCs, and the obtained operating region of MMCs is not optimal when the CMR is used as the indicator in the parameter design of MMCs. In contrast, the DMR-based evaluation method is high-accurate under all situations. Finally, experiments are carried out in a down-scaled MMC prototype for further validating the method.
ISSN:2168-6777
2168-6785
DOI:10.1109/JESTPE.2021.3135307