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.
Highlights
To achieve the targets of sustainable development and copying with climate change, developing renewable energy has been widely recognized as a key solution
The line commutated converter (LCC)-high-voltage direct-current (HVDC) technology has developed to a high degree of maturity in the past decades
(UHVDC) link has reached to ± 1100 kV with a capacity of 12 GW [7]
Summary
To achieve the targets of sustainable development and copying with climate change, developing renewable energy has been widely recognized as a key solution. With the fast development in the past two decades, the converter capacity and voltage level of MMC-HVDC technology have been achieved in UHVDC levels [11,12] This makes the hybrid DC transmission systems which utilize both LCCs and MMCs in UHVDC applications become possible. Reference [22] investigates fault protection methods in LCC HVDC systems using bypass valves It does not consider the full-voltage to half-voltage operation and control. In [24,25], valve-group bypassing strategies of LCC-UHVDC systems have proposed They have not provided methods to minimize the load-shedding when one pole gets into the half-voltage operating mode. They have not considered the control strategies for hybrid LCC/MMC UHVDC systems. The proposed full-voltage to half-voltage control strategies and the power reschedule strategy have been verified in LCC and hybrid LCC/MMC UHVDC systems built in PSCAD/EMTDC
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
