The Study Of LVRT Capability Simulation Of Direct-driven Permanent Magnet Wind Power Generator Unit

With the rising of public awareness for environment protection, the wind energy, as a clean, renewable energy,is attached great importance to by countries all over the world, and wind power generation has become an important development direction of many countries’energy strategy.Direct-driven permanent magnet synchronous generator wind turbine (PMSG-WT) has no gear boxes and exciting windings,thus it is simple in structure and flexible to control and has become Mainstream models. Direct-drive permanent magnet wind turbine after back-to-back full power converter is connected with power grid.when the grid voltage drops, wind turbine off-grid operation will exert serious impact on the stability of the grid. This dissertation focuses on research work on how to improve the low-voltage operation capability of direct-drive permanent magnet wind turbines.Firstly, the current development status of wind power generation and the impact of large-scale wind power integration on power system stability is discussed, and the necessity to study the low voltage operation capacity of direct-drive wind power generators is pointed out.Secondly, the work characteristics and operation principles of direct-drive wind power generators are analyzed, and the mathematical models of the permanent magnet synchronous motor and power converter are built based on the dq Synchronous rotation coordinate system. On this basis, the power extraction control model, in which the rotor speed is control object, the generator rotor flux linkage vector oriented control strategy, and the grid side converter grid voltage vector oriented control strategy are proposed.Thirdly, the operation property of the permanent direct-driven wind generator system when the grid voltage drops is studies, a novel LVRT coordinated control strategy is proposed, in which the generator output power reduction, unloading resistance control and pitch angle control are combined.This strategy aims at avoiding generator over-speed and DC capacitor over-voltage, thus the safe operation of the generator and converters can be ensured. At the same time, the frequency of unloading resistance will be reduced.Finally,electromagnetic simulation system of PMSG-WT is established with the software package PSCAD/EMTDC,and the examples on three-phase short circuit fault occured are designed to validate the LVRT coordinated control strategy.The simulation results testify the effectiveness and correctness of the proposed strategy.coordinated control strategy.The simulation results confirm the effectiveness and correctness of the proposed strategy.