Aiming at one of the full-capacity voltage source converter based ultra-high voltage direct current (VSC-UHVDC) engineering technical solutions

the researches on a symmetrical bipolar main topology system with dual valve groups are carried out without DC circuit breakers or adopting DC fast switches for engineering applications. The AC and DC charging conditions of the system are analyzed and a low-impact and low-disturbance start-up control strategy is proposed for the operation without DC circuit breakers. Finally

a full-capacity VSC-UHVDC system without DC circuit breakers is built on RTDS simulation platform

and the proposed topology

charging strategy and start-up control strategy are verified through real-time simulation. Simulation results show that the developed start-up strategy for full-capacity UHV flexible DC transmission system can solve the inability to start the flexible HVDC transmission system without DC circuit breakers

reduce voltage/current disturbances during start-up

and mitigate overvoltage/overcurrent risks of the equipment

which is valuable for engineering applications.