Two new techniques to solve the problems with multi-infeed HVDC systems

The multi-infeed HVDC problems are the limiting factors for the application of the dc technology in the long-distance bulk-power transmission in China. Thus, this paper presents two new techniques to solve these problems: one is the grid dynamic segmentation technique and the other is the VSC-HVDC technique. Firstly, two aspects of the multi-infeed HVDC problem, i.e. concurrent commutation failure caused by ac short-circuit faults and power flow shift caused by bipolar faults of dc systems, are revealed based on the analysis of their physical mechanisms. Then, the large-impedance fault current limiter is used to fulfill the grid dynamic segmentation, which proves to be effective in solving the concurrent commutation failure problem. After that, the VSC-HVDC technique is used to eliminate both the problems with the multi-infeed HVDC system. Some important issues with the realization of the bulk-power VSC-HVDC overhead transmission, like the grounding mode selection, the bulk-power assembly converter, and the dc line fault self-clearing capability are also discussed and solved.