The Study On The Control Technology Of FRT Capability Of Double-Fed Induction Generators Based On D-STATCOM

With the rising of public awareness for environment protection, the wind energy, as a clean and renewable energy, is attached great importance by countries all over the world, and wind power generation has become an important development direction of many countries’energy strategy. Doubly-Fed Induction Generator (DFIG) has an ocean of advantages, such as smaller rating of excitation converter, high wind energy utilization, low cost and flexible control method, thus it has become the mainstream models. The stator of DFIG is connected to the grid directly where the rotor current is controlled by excitation convertor, which indirectly regulating power output of grid side, and this structure makes the fault ride through (FRT) capability weak. So this dissertation focuses on research work on how to improve the FRT capability of DFIG.The current development status of wind power generation and the impact on large-scale wind power integration to power system stability are discussed in this thesis, and the necessity to study the FRT capacity of DFIG is pointed out. Then the current development status of Distribution Flexible AC Transmission Systems (DFACTS) is introduced also.The dynamic model of DFIG is established in the d-q synchronous rotation coordinates. On this basis, the vector control strategy of converter is established. The vector control strategy of stator flux oriented is adopted by the rotor side converter, and the vector control strategy of grid voltage oriented is adopted by the grid side converter. A simulation results show that FRT capability of DFIG is very limited. In order to further enhance this capability, this thesis proposes the control strategy based on the dynamic reactive power compensation. And the dynamic model of Distribution Static Synchronous Compensator (D-STATCOM) is established in the d-q synchronous rotation coordinates. On this basis, the operating principle of reactive compensation is introduced when the grid voltage sags or swells; the feed-forward decoupling control strategy of stator voltage oriented is analyzed.Finally, the transient characteristic of DFIG is deduced when the grid voltage symmetry sags or swells. Simulation system of DFIG containing the D-STATCOM device is established with the software PSCAD/EMTDC, and the examples on three-phase short circuit fault occurred are designed to validate the LVRT and HVRT coordinated control strategy. The simulation results testify the effectiveness and correctness of the proposed strategy.