Modeling And Simulation Analysis Of NingDong HVDC System Based On PSCAD

With the powerful impetus of the strategy-power grid interconnection and power transmission from west to east in China, the HVDC has been occuping a more important place in power grid layout in China, which has a remarkable advantage over long-distance and large-capability electricity transmission, as well as regional power grids interconnection. Ningdong DC system is an important part of the strategy-power transmission from west to east in China, which lies from Yinchuan east converter station in the west, and to qingdao jiaodong converter station in the east. It is the first HVDC project with the voltage level of±660kV, and is also the first HVDC project set in Shandong province. With the commissioning of the project, the Shandong power grid has steped into the operation state of AC-DC hybrid power system.The special voltage level of Ningdong DC system also means higher request for the electric design and device performance of the system, which bring new chanlenges to the safe and stable operation of the Ningdong DC system and the Shandong power grid. Therefore making modeling and simulation analysis of Ningdong HVDC system and research on the mutual influence between AC and DC system, realizing the transient characteristics of the system under different faults are of great importance for the stable operation and fault handling of the system.This thesis makes detailed modeling and simulation work of the Ningdong HVDC system based on the actual operation parameters of the project in the platform of the power system simulation program PSCAD/EMTDC, including the DC part modeling and the AC system modeling. And then makes simulation research on the mutual influence between AC and DC system baesd on the model established in above step.What is first complished in this thesis is the DC part modeling of the Ningdong HVDC system, including main circuit modeling and control circuit modeling. The main circuit modeling covers main circuit electric equipments modeling-convertor, converter transformer, AC filter, DC filter, smoothing reactor and DC transmission line. Different control modes are used in the rectifier side and the inverter side, the control circuit modeling of equipments in the two poles are made in detail. Then the AC system modeling lying in the two sides of the DC system is made, in whihc the Northwest power grid is replaced using thevenin equivalent circuits, as to the Shandong power grid, this thesis makes dynamic equivalence using Power System Analysis Software Package(PSASP) based on thysical equivalent principle, converter bus, key bus and other grid node focused are retained, and the rest are equivalent. Then the Shandong power grid modeling in PSCAD are made according to the equivalence results.At last, thesis makes research on the mutual influence between AC and DC system based on the model established,which mainly includes:the transient response characteristics analysis of the system under the DC transmission line fault which is set in the smoothing reactor outlets of the DC line in the rectifier side and inverter side; the transient response characteristics analysis of the system under DC block, making analysis about overvoltage phenomenon due to DC block; the transient response characteristics analysis of AC system fault in Shandong power grid, which set faults in different places of Shandong power grid with different voltage levels, makes comparative analysis of system response under different faults and focus on the commutation failures phenomenon of the HVDC system. Obtaining the system transient response characteristics, this thesis makes detailed mechanism analysis and provides measures suggestions on treatment and prevention of the faults.