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

With the rapid development of the new energy,the grid-connection capacity ofWTGS (wind turbine generator system) increases continuously and wind turbine hasbeen an important area of energy development all over the word. If the wind powersystem,within a grid that has a high wind power ratio, off the system on a large scaleduring the voltage drop, might cause huge damage.thus it is essential to improveperformance in low voltage so as to maintain grid-connected operation till thetrouble is cleared. This essay focus on researches related to improving performancedirect-driven permanent synchronous generator in low voltage.At the beginning, this essay offers a brief instruction of the background andcurrent development of the wind turbine wordwide and analyses relevant rules ofLVRT (low voltage ride through),pointing out the importance of the theoreticalresearch of functional capacity of direct-driven permanent magnet synchronousgenerator in low voltage.Secondly, the work characteristics and operation principles of direct-drive windpower generators are analyzed, and the mathematical models of the permanentmagnet synchronous motor and power converter are built based on the dqSynchronous rotation coordinate system. On this basis, the power extraction controlmodel, in which the rotor speed is control object, the generator rotor flux linkagevector oriented control strategy, and the grid side converter grid voltage vectororiented control strategy are proposed.Thirdly, the operation property of the permanent direct-driven wind generatorsystem when the grid voltage drops is studies. a novel LVRT coordinated controlstrategy is proposed, in which the generator output power reduction, unloadingresistance control and pitch angle control are combined.This strategy aims atavoiding generator over-speed and DC capacitor over-voltage, thus the safe operation of the generator and converters can be ensured. At the same time, thefrequency of unloading resistance will be reduced.Finally,electromagnetic simulation system of PMSG-WT is established withthe software package PSCAD/EMTDC,and the examples on three-phase shortcircuit fault occured are designed to validate the LVRT coordinated controlstrategy.The simulation results testify the effectiveness and correctness of theproposed strategy.coordinated control strategy.The simulation results confirm theeffectiveness and correctness of the proposed strategy.