Research On Control Strategy Of Direct-Driven Permanent Magnet Wind Generator

With the rapid development of the new energy industry,the grid-connection capacity of wind turbine generator system increases continuously and wind turbine has been an important area of energy development all over the word.If the wind power system,within a grid that has a high wind power ratio,off the system on a large scale during the voltage drop,might cause huge damage.thus it is essential to improve performance in low voltage so as to maintain grid-connected operation till the trouble is cleared.When traditional unloading resistance realizes low voltage ride through(LVRT),unbalanced power on both ends of the DC side is consumed in the form of heat energy,which is not able to solve the problem of DC bus voltage rise in the long time.A new control strategy of LVRT has been put forward.At the beginning,the work characteristics and operation principles of permanent magnetic synchronous generator(PMSG)are analyzed,and the mathematical models of PMSG and power converter are built based on the stationary and dq synchronous rotation coordinate system,which realizes decoupling control of d axis and q axis.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.Secondly,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 safeoperation 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 is established with the software package MATLAB,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.