Research of hybrid active filter protection scheme for LCC-UHVDC transmission system

For traditional passive filters have many disadvantages, such as large occupation of area, prone to resonance with the impedance of AC power system, therefore the cascade H-bridge hybrid active filter was adopted as AC side filter of LCC-UHVDC transmission project in China, which adopts a scheme of 12 / 24 dual-tuned filter directly connected in series with the active filter based on cascade H-bridge. This article proposes a protection configuration scheme of hybrid active filter for LCC-UHVDC transmission, At the same time, this article optimize the design of the protection software and hardware architecture. The protection device uses dual-CPU 'AND' outputs to eliminate mis-action caused by the damage of a single device or a single loop. As the action time of hybrid active filter protection has become longer due to the addition of an active filter, this article utilizes differential protection comprehensive optimization technology, logic operation parallel processing technology, and relay asynchronous startup technology to compress the overall action time of protection system. The performance of hybrid active filter protection device developed based on the above design scheme can meet the technical specifications for UHV DC transmission system.