Control of Offshore MMC During Asymmetric Offshore AC Faults for Wind Power Transmission

The adoptions of medium voltage in ac collection networks of large dc-connected wind farms significantly increase the ac current magnitudes during normal and fault conditions. Controlling fault currents at zero during asymmetric ac faults is possible, but it has several drawbacks such as increased r...

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Bibliographic Details
Published in:IEEE journal of emerging and selected topics in power electronics 2020-06, Vol.8 (2), p.1074-1083
Main Authors: Shi, Lei, Adam, Grain Philip, Li, Rui, Xu, Lie
Format: Article
Language:English
Subjects:
Alternating current
Asymmetric AC faults
Asymmetry
Circuit faults
Converters
Electric potential
Fault currents
Faults
high voltage DC (HVDC) transmission
HVDC transmission
modular multilevel converters (MMCs)
negative sequence control
Offshore
offshore wind farms (OWFs)
Power electronics
Recovery
Voltage control
Wind farms
Wind power
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Summary:The adoptions of medium voltage in ac collection networks of large dc-connected wind farms significantly increase the ac current magnitudes during normal and fault conditions. Controlling fault currents at zero during asymmetric ac faults is possible, but it has several drawbacks such as increased risk of protection mal-operation due to the absence of fault currents, which also tends to prevent the recovery of ac voltage in postfault. Therefore, this paper presents an enhanced control strategy that exploits the induced negative sequence voltages to facilitate controlled injection of negative sequence currents during asymmetric ac faults. The proposed control not only defines a safe level of fault current in the offshore ac network but also instigates immediate recovery of the ac voltage following clearance of ac faults, which avoid protection mal-operation. In addition, the positive sequence voltage set-point of the offshore modular multilevel converter (MMC) is actively controlled by considering the negative and zero sequence voltages, which effectively avoids the excessive overvoltage in the healthy phases during asymmetrical ac faults. The theoretical basis of the proposed control scheme is described and its technical viability is assessed using simulations.
ISSN:2168-6777
2168-6785
DOI:10.1109/JESTPE.2019.2930399