| As the comprehensively promotion of "Transmission from west China to east China" and large-scare interconnected power grid projects in China, HVDC has become the most important channel for interregional power transmission. At present, the mixed AC and DC operation pattern has also been established gradually. Though many advantages of HVDC have been verified in far distance and large capacity power transmission, there are also some potential issues in the development of DC transmission. As the most important and complicated part of HVDC transmission system, converter station is also the place where faults frequently occur. Compared with traditional AC system, the operation mode, control and protection strategy, forms of faults, and mechanism of converter station are quite different. Faults of converter station will cause great power loss, the imbalance of its receiving-end AC system’s efficiency, and voltage instability. And the collapse of the whole AC and DC system will probably happen if the receiving-end system is weak and some faults were treated improperly. Thus, the analysis of the impact of converter station in different faults occasions on regional power grid has very significant meaning in ensuring the safe and stable operation of HVDC and its receiving-end system.Based on the±800kV Nuo Zhadu HVDC project and the technology project of CSG "An analysis of the converter station’s influences on Jiangmen Power Grid", this article has taken the basic working principles, features of control system, configuration and function of protection system of converter station into the scope of research. And with PSCAD/EMTDC electromagnetic transient simulation program, not only the corresponding simulation models of±800kV dual12-pulse HVDC transmission system and AC system of220kV and above receiving-end system have been built; but also the accurate simulation of real projects has been realized.Started with its mechanism, the process and various influential factors of commutation failure have also been studied. With the help of operation circuit method, this article also analyzes the changes of DC and AC currents when there are commutation failures, and the influences caused by injecting high harmonic currents and capacitive currents into receiving-end system. And the simulation analysis of the commutation failures caused by too small positive advanced triggering angle of inverter station and three-phase short circuit of AC system line, and it’s influence on receiving-end power grid, helped us find the critical resistance value for no commutation failure occurrence when three-phase resistance ground.Moreover, this research also analyzed the mechanism and process of common types of short-circuit faults in inverse transformation station, and their possible influence on receiving-end AC system, with the simulation analysis on typical occasions of each kind of short-circuit fault. Meanwhile, the impact of the electromagnetic transient process, the corresponding adjustment measure of control system of DC system in four faults occasions on receiving-end AC system has also been studied. And the conclusion and also comparisons between receiving-end data have also been made. Finally, with the purpose of ensuring the safe and stable operation of receiving-end system, the researcher has put forwarded the measures to decrease the impact of converter station’s faults on receiving-end power grid; and analyzed faults’effects in different short circuit ratio occasions, configuration optimization of converter station, and the influence of DC control modes on AC system. |
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