Two New Technologies for Eliminating the Problems with Multiple HVDC Infeeds

Two new technologies for eliminating the problems involved with multi-infeed HVDC systems,i.e.the grid dynamic segmentation technology and the VSC-HVDC technology are presented in this paper.Based on the analysis of the mechanisms of the HVDC multi-infeed problems,two aspects of the problems are identified,i.e.the simultaneous commutation failures caused by AC network faults and the large area great power flow shift caused by bipole faults of some HVDC systems.In connection with the approaches to fulfill the grid dynamic segmentation,the paper proposes an approach with large-impedance fault current limiter,and illustrates the effectiveness of the grid dynamic segmentation to solve the simultaneous commutation failure problem.The effectiveness of the VSC-HVDC to eliminate the two aspect problems of multi-infeed HVDC systems is also discussed,while the associated problems with bulk power overhead transmission for VSC-HVDC,such as the grounding mode selection,the bulk power converter assembly composed of multiple series and parallel connected converter units,and the DC side fault selfclearing capability,are analyzed.