Research On Fault Ride Through Control Strategy Of Wind Farm Connected To Grid Based-On VSC-HVDC

As a renewable energy power, wind power has the most large-scale development and commercial prospects. In recent years, wind power got a rapid development benefited from the positive national policy. At the same time, strict requirements had been put forward for the grid-connected wind farm, included a fault ride through (FRT) ability. Because of the unique technical advantages, VSC-HVDC is very suitable to be applied in renewable energy power generation, grid-connected distributed generation, isolated island and the city power supplied, connection of asynchronous AC power grid, etc. In part, for a grid-connected wind farm, the fault can be isolated by VSC-HVDC system. Accordingly, VSC-HVDC is considered to be the ideal connecting grid mode for offshore wind farm.Firstly, this paper selected the most received doubly-fed induction generator (DFIG) as the object of study. Established its mathematical model. According to the mathematical model of DFIG in d-q synchronous rotating frame, control strategy of rotor side and grid side convert base on stator flux and voltage vector orientation vector control principle was design. Then establish the simulation model of DFIG in PSCAD/EMTDC.Secondly, analysis the principle of VSC-HVDC based on its mathematical model. Studied in the control strategy of VSC-HVDC converter station with different situations. According to the wind farm operation characteristics, this paper designs the control strategy for the converter, which is used for the system of wind farm connected to grid based-on VSC-HVDC. Then, the simulation model of grid-connected system is established and verified through the simulation analysis in PSCAD/EMTDC.Finally, the operation characteristics of wind farm connected to gird based-on VSC-HVDC system are analyzed. According to the situation that the symmetrical fault occurs in the grid, the DC chopper is activated to dissipate the surplus active power that cannot be transmitted to AC system. An adaptive resistance topology structure is developed, and a coordinated control strategy with the topology structure is designed to maintain the active power balance of the system during fault. And then, the given methods of FRT are carried out with the simulation model of grid-connected system built in PSCAD/EMTDC. The simulation results show that the methods of FRT can maintain the stable operation of the system, and the wind farm avoid fault successfully. By contrast, adaptive resistance topology structure and the coordinated control strategy improves grid-connected system FRT ability effectively.