Investigation of interconnecting two Chinese LCC-HVDC through LCL DC/DC converter

In order to increase the operating flexibility and reliability of HVDC lines for power transmission, this paper studies the technical feasibility of interconnecting two Chinese LCC HVDC using a high power DC/DC converter. A new control system is proposed for each rectifier, inverter and DC/DC converter to enable independent operation of each terminal. DC voltage droop feedback is designed to moderate power order at each terminal which facilitates DC power balancing without communication between terminals. Simulation on detailed PSCAD model is presented for several extreme operating scenarios and responses confirm many operational benefits of the proposed topology. Loss of one terminal in this 4-terminal DC grid, for example, will not disturb operation of the remaining 3 terminals. This preliminary study concludes that there are no serious technical challenges, while operating benefits might be significant.