The thyristor triggering and monitoring(TTM)unit is one of core devices of HVDC converter valve

which is used for photoelectric conversion of signals between valve control system and converter valve. TTM unit can realize the triggering and protection of converter valve

and its performance directly influences the reliability of HVDC transmission project. This paper presents the functional design block diagram of the TTM with composite energy harvesting function under the high potential mode. And the effect of the work state of TTM on HVDC transmission system with fault of AC system is analyzed. Then a design method of energy storage circuit of TTM is proposed. Finally

the effectiveness of TTM with energy storage circuit is verified through theoretical calculation

simulation and experimental based on ±800 kV/5 000 A Jiuquan-Hunan HVDC project. The TTM of A5000 converter valve with this achievement as the core technology has been applied to multiple DC transmission projects.