Power system simulation is an important way to study UHVDC transmission technology features and functions. In order to test the integrated secondary equipment for ±800kV UHVDC transmission project and study the interaction of AC/DC system

the RTDS real-time digital simulation platform is presented in this paper. By connecting all kinds of RTDS input/output interface card with DC control and protection device

converter valve control equipment and secondary equipment such as measuring interface screen

the control closed-loop simulation system is constituted. In view of RTDS hardware platform upgrade and interface characteristics of the converter valve control system

the interface mode between the simulation platform and various types of secondary equipment are introduced in detail

and the fiber enhanced backplane of PB5 processor is used to increase node calculate numbers of the RTDS rack. Based on RTDS closed-loop simulation platform

taking the additional control function of DC control and protection device for example

the DC power modulation test is carried out. The simulation results verify the validity of frequency control function for the DC control and protection device.