Analysis On The Operation Performance In Mult-infeed HVDC System

In the purpose of meeting the unbalanced regional energy distribution and economic development, the government made a strategic target that is to develope hydropower, thermal power and renewable energy bases in the western and northern part and implement transmitting power from West to East and nationwide power grid interconnection. In 2020, China will build a national backbone grid consisting of 1000kV AC system and±800kV HVDC system. After the formation of the UHV Power Grid, multi-infeed HVDC system will emerge in some areas. According to the UHV Power Grid planning, the terminals of 8 HVDC transmission lines will be in East-China power grid in 2015, the interaction between AC and DC systems will become more complicated. It's necessary to study the operation performance in Multi-infeed HVDC system.The equivalent power grid in 2015 is established using the EMTDC/PSCAD electromagnetic transient simulation software to study the operation performance in Multi-infeed HVDC system. The main research conclusion are listed as follows:(1) The methods of establishing all-digital electromagnetic transient simulation system with large-scale multi-infeed HVDC system are studied, including the dynamic equivalence, EMTDC model establishment, and the dynamic performance checking. The simulation means of analyzing the operation performance in multi-infeed HVDC system under Ultra High Voltage Power Grid is provided.(2) In order to provide analysis methods and ideas for the study on operation performance in Multi-infeed HVDC system, the mechanism of commutation failure in Multi-infeed HVDC system is comprehensively analyzed. Several factors that may cause commutation failure are studied, such as transient voltage changes and voltage decreasing rate, commutating voltage zero-crossing phase shift, AC system short circuit current level, sudden increase of DC current, and HVDC control and protection characterastic. (3) The commutation failure caused by the AC system faults at the receiveing side is studied deep. The study results show the commutation failure takes place at more than one HVDC systems simultaneously, but the HVDC systems can return to normal operation after faults clearing. The technical feasibility for the focus of eight HVDC terminals in east china is verified.(4) The thesis makes overall research on the security and stability of UHV AC-DC hybrid transmission system. The system can maintain stable operation when the N-1 fault happens. When N-2 fault happens, the system can be kept stable with security and stability measures. So it's proved that the security and stability of UHV AC/DC hybrid transmission system meets the requirements of "Power System Security and Stability Guide".(5) To improve system security and stability of UHV AC-DC hybrid transmission system, the Emergency upgrade of dc power and Strengthen dynamic reactive power compensation measures are simulated to provide the technical reference.