Control Strategies of Full-Voltage to Half-Voltage Operation for LCC and Hybrid LCC/MMC based UHVDC Systems

Gen Li, Wei Liu, Tibin Joseph, Jun Liang, Ting An, Jingjing Lu, Marcio Szechtman, Bjarne Andersen and Qikai Zhuang
Additional contact information
Gen Li: School of Engineering, Cardiff University, Cardiff CF24 3AA, UK
Wei Liu: School of Engineering, Cardiff University, Cardiff CF24 3AA, UK
Tibin Joseph: School of Engineering, Cardiff University, Cardiff CF24 3AA, UK
Jun Liang: School of Engineering, Cardiff University, Cardiff CF24 3AA, UK
Ting An: Global Energy Interconnection Research Institute, Beijing 102211, China
Jingjing Lu: Global Energy Interconnection Research Institute, Beijing 102211, China
Marcio Szechtman: Eletrobras Cepel, Rio de Janeiro 26053-121, Brazil
Bjarne Andersen: Andersen Power Electronic Solutions, Bexhill-On-Sea TN39 4QL, UK
Qikai Zhuang: Global Energy Interconnection Research Institute Europe GmbH, Kantstr, 162 Berlin, Germany

Energies, 2019, vol. 12, issue 4, 1-17

Abstract: With the increasing demand of transmitting bulk-power over long-distance, the ultra high-voltage direct-current (UHVDC) transmission systems become an attractive option. Nowadays, not only the line commutated converter (LCC) based systems, but also the modular multilevel converter (MMC) based systems have reached UHVDC levels. The converter stations of UHVDC systems normally utilize two series-connected valve-groups to reduce the difficulties of device manufacturing and transportation. This high-voltage and low-voltage valve-group configuration allows the UHVDC systems to achieve a full-voltage to half-voltage operation which increases the flexibility of the systems. However, the existing research only focuses on the full-voltage to half-voltage control of LCC-UHVDC systems. The control strategies for hybrid LCC/MMC UHVDC systems are underresearched. Moreover, the approaches to reduce the load-shedding caused by the full-voltage to half-voltage control for both LCC and hybrid LCC/MMC based UHVDC systems have not been investigated. In this paper, full-voltage to half-voltage control strategies for both LCC and hybrid LCC/MMC based UHVDC systems have been proposed. Moreover, to avoid load-shedding caused by the half-voltage operation, a power rescheduling method that re-sets the power references of the half-voltage operating and full-voltage operating poles has been proposed. The proposed full-voltage to half-voltage control strategies and power rescheduling method can achieve a stable and fast control process with a minimum power loss. The proposed methods have been verified through the time-domain simulations conducted in PSCAD/EMTDC.

Keywords: UHVDC; line commutated converter; modular multilevel converter; hybrid LCC/VSC; power rescheduling; half-voltage operation; valve bypassing (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2019
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