The Research Of VSC-HVDC Transmission Technology On The Application Of Offshore Wind Farm

With the continuous development of wind-power market and the shortage of land resources, each country has attached importance to the development of the offshore wind farm. But the intermittent and randomness of the wind turbine power will significantly affect the power quality of the power grid. The voltage source converter high voltage direct current transmission(VSC-HVDC)will be widely used at network synchronization of the offshore wind farm because of the flexible power control capability.In this paper, the working principle and mathematical model of double-fed induction generator(DFIG), which is as the main machine type of the wind turbine generator, were analyzed, the vector control strategy with the stator voltage vector oriented and the line side voltage oriented were proposed, the power decoupling of the double-fed induction wind turbine was achieved firstly; Combined with the characteristics of offshore wind power generation, the network synchronization technology and development trend at home and abroad, the working principle and mathematical model of VSC-HVDC were analyzed. In order to realize the steady-state operation control of active and reactive decoupling of the whole system the coordinated control strategy of VSC-HVDC suitable for offshore wind farm was designed, which means offshore wind farm converter(VSC1)used the vector control strategy of fixed active power and fixed reactive power ,onshore converter(VSC2)used the vector control strategy of fixed dc voltage and fixed ac voltage.In order to verify the superiority of wind farm with the network synchronization mode of VSC-HVDC, the simulations based on the PSCAD/EMTDC simulation platform are as follows: First, it can be seen from the simulation results that VSC-HVDC can transfer the wind power in time under the condition that the wind velocity changes, and the dc transmission line and the voltage of the two ac sides are stability; secondly, it can be seen from the simulation results that VSC-HVDC can maintain the voltage stability of the wind farm, realize that the wind turbine can ride through the short circuit fault and has a obvious advantage combined with the ac network synchronization mode when the net-side has been set the short circuit fault with different network synchronization modes (ac network synchronization mode and VSC-HVDC network synchronization mode); Finally, it can be seen from the simulation results that the VSC-HVDC transmission system can isolate the faults happened during transient process and prevent further expansion of the faults when the wind farm side and net side have been set the short circuit faults at VSC-HVDC network synchronization mode.