Real time digital simulation of the parallel multi-terminal HVDC transmission system

Multi-terminal HVDC refers to an HVDC system that consists of three or more converter stations. When power is to be transmitted from different remote generation locations to different load areas, it may be economically and flexible using Multi-terminal HVDC. In this paper, based on the RTDS and the MTDC control and protection equipment developed by Nari-relays Electric CO.,LTD., the real time closed loop simulation model of a ±500kV, 5000MW bipolar four-terminal HVDC transmission system is developed. The control strategy employed for the system is the current margin method. The hierarchy of MTDC control and protection system include master control and converter station control, the master control coordinates the control of the terminals with the functions such as balancing power orders, ramping orders, dc voltage orders and communication etc., the converter station control with the function to control the power of the stations such as bipolar control and pole control. The transient faults such dc line fault and ac system fault have been simulated, and the simulation results show that the proposed control strategy and the MTDC control protection system can meet the requirements of the operation of the MTDC transmission system, and also some conclusions are drown from the results of the simulation.