An increasing number of HVDC lines are currently deployed all around the world. HVDC links are either based on line-commutated converters (LCC) or on voltage-source converters (VSC) technologies. This paper presents a fundamental study on the impact of HVDC links on the transient stability of power systems. Both, VSC and LCC HVDC links have been studied when applied to a two-area power system. Particular attention has been paid to the critical clearing time (CCT). It has been found that HVDC links generally improve transient stability by increasing the critical clearing time with respect to the case without HVDC link. Moreover, the impact on transient stability significantly depends on the supervisory control strategies applied to the LCCs and VSCs of the HVDC links. An inappropriate handling of current limits of VSC by reducing either active or reactive power can worsen transient stability.
Keywords: Transient stability, VSC HVDC link, LCC HVDC link.
Published: June 2015.