The Study Of Affect Between HVDC-system And AC-system With Large-scale Wind Farms

With the large-scale wind farms in the Northwest built and DC transmissiontechnology development and maturity, HVDC has become the best way of Northwestwind power outgoing, forming a HVDC transmission coexist with AC-system, theinteraction between AC-systems and DC-system have become the focus of ourattention.Firstly, this paper studied the composition and characteristics of DFIG, establishedthe mathematical models of wind speed, wind turbine, generator and the inverter, thenequivalent the large-scale wind farm into one wind turbine, and build the equivalentDFIG in PSCAD. Then analyze the principle of HVDC systems, derive a mathematicalmodel of HVDC system, formulate the control strategies by comparing several controlmodes, verify the model and control strategies in PSCAD by simulating. Establish threeAC-DC system topologies with large-scale DFIG wind farms:(a) The two AC and DCtransmission systems are both use parallel, each AC-DC transmission system will sentthe power to the same AC system through parallel;(b) The two AC and DCtransmission systems are both use non-parallel, each AC-DC transmission system willsent the power to the two different AC system through non-parallel;(c) One AC-DCtransmission systems use parallel transport, and another AC-DC transmission systemuse non-parallel transport. On this basis, research and analysis the mutual influencebetween AC systems and DC systems. Through the simulation, analysis the AC systemeffects on DC system while the wind speed fluctuating, PCC short-circuit faulting,750kV bus of AC transmission system faulting, compare the of the above threeoperation modes. Discuss the AC system voltage stability influenced by DC systemcontrol strategies and reactive power compensation capacity, simulate and analysis theDC system impact on the AC system while the DC system faulting and different AC-DCproportional under three operating mode. Obtain the results of interaction between theAC-DC system, and to help the stability of the power grid.