Enhanced flat-topped modulation for MMC control in HVDC transmission systems

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Li, Rui and Fletcher, John E. and Xu, Lie and Williams, Barry W. (2017) Enhanced flat-topped modulation for MMC control in HVDC transmission systems. IEEE Transactions on Power Delivery, 32 (1). pp. 152-161. ISSN 0885-8977 (https://doi.org/10.1109/TPWRD.2016.2561929)

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Abstract

Flat-topped modulation is a member of the family of triplen-series injection techniques that have been extensively utilized in PWM inverter systems to increase the DC-link, and hence semiconductor, utilization. We propose the use of an optimized flat-topped modulation scheme for the modular multilevel converter (MMC) control. The optimized flat-topped waveform minimizes the magnitude of the triplen harmonics, particularly compared to the popular space-vector modulation (SVM) technique, while fully utilizing the DC voltage. This has particular advantages if the converter-side of the interfacing transformer is earthed. Under such conditions, the zero-sequence earthing current is affected by the triplen series injected into the sinusoidal modulating functions. Therefore, it is critical to minimize the injected triplen harmonics. The operating principle of the flat-topped scheme is presented and the Fourier coefficients are compared with the SVM technique. Additionally, the influence of the proposed control scheme on MMC performance is evaluated mathematically. Simulation of a point-to-point HVDC link using average model demonstrates the effectiveness of the proposed MMC operational schemes. The third harmonic of the flat-topped modulation is reduced by 33%, which lowers the potential zero-sequence current flowing to earth. Compared to conventional sinusoidal modulation, the submodule capacitance is reduced by 25%. This significantly lowers submodule cost, volume, and weight. Station conduction losses are expected to reduce by 11%, yielding higher efficiency and lowering cooling system capacity. In addition to the improvement under normal operation, the proposed control scheme also reduces the fault current by 13.4%.

ORCID iDs

Li, Rui ORCID logoORCID: https://orcid.org/0000-0001-8990-7546, Fletcher, John E., Xu, Lie ORCID logoORCID: https://orcid.org/0000-0001-5633-7866 and Williams, Barry W.;
  • Item type:Article
    ID code:56271
    Dates:
    Date
    Event
    1 February 2017
    Published
    3 May 2016
    Published Online
    18 April 2016
    Accepted
    Notes:(c) 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.
    Subjects:Technology > Electrical engineering. Electronics Nuclear engineering
    Department:Faculty of Engineering > Electronic and Electrical Engineering
    Depositing user: Pure Administrator
    Date deposited:04 May 2016 09:15
    Last modified:11 Nov 2024 11:25
    Related URLs:
    URI:https://strathprints.strath.ac.uk/id/eprint/56271
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