| With the development of power system, as well as the rapid growing requirement of power transmission, direct current (DC) transmission has been more and more important. While alternating current (AC) transmission faces the question of low frequency oscillation, angle stability and the difficult to long distance transmission, DC projects is applied widely in the link between AC systems and big amount & long distance active power transmission. There will be about 30 DC project in China by 2020, including at least 6 ultra high DC project, forming two multi-infeed power systems, i.e. Yangtze Delta and Pearl Delta.DC transmission also has its own problems besides its advantages. In China, the DC projects are built for the hydro power transmission from southwest to Yangtze Delta & Pearl Delta, the influence on receiving network is hard to predict but of course great. Based on the fact of DC projects in China, the thesis includes a series of analysis on the features of DC projects and multi-infeed grid:1) Introduce the concept of short circuit ratio (SCR), multi-infeed short circuit ratio (MSCR), as well as the steady-state and transient-state features of DC system; moreover, state the application range and limitation of SCR &MSCR.2) Based on comprehension of electromechanical and electromagnetic transient modeling, this article studies the modeling and simulation of large scale multi-infeed AC-DC grid in EMTDC/PSCAD.3) Make an introduction to the theory and features of DC transmission, and study the DC control and protection systems in Yangtze Delta, get the control features in Yangtze Delta DC project.4) Build the electromagnetic model of Yangtze Delta AC-DC grid, and prove the accuracy and availability of the model by power flow checking, DC parameters checking and fault checking.5) Apply the model built above on analysis of commutation failure, and get the critical AC voltage by simulation, providing a reference for East China nower svstem network construction. |
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