(NR Electric Co. Ltd., Nanjing 211102, China)

Paralleled high voltage direct current (HVDC) is a special way of multi-terminal HVDC, the expansion scheme is economical, flexible and convenient. Real time digital simulator (RTDS) is used to develop a ±800 kV paralleled double converter and a 10 GW bipolar HVDC simulation model. The HVDC control and protection model uses control and protection demo machines as the prototype and RTDS to constitute a real-time closed loop simulation test environment. The current margin control is used as the control strategy, and constant current control is adopted for both converters at rectifier side, while at the inverter side, one converter uses constant current control, the other one uses constant voltage control. The control system architecture is set after the bipolar/pole layer control, converter layer control. The converter control layer realizes the two converter triggering control, and bipolar/pole control layer generates current and voltage reference value instructions. After allotment, the instructions are sent to the converter layer control. Start and stop pole, steady state operation and online entry and exit of the converter are simulated using this simulation system. The simulation results show that the proposed control strategy and the developed control protection equipment meet the requirement of dual converter paralleled HVDC transmission.