An Control Strategy Of Direct-Drive Permanent-Magnet Wind Power System For Low Voltage Ride Through

Energy shortage has become an important issue of global concern,with the economic development and growth of population,development and utilization of new energy sources has become particularly important.Wind power is a clean energy with mature technology,which has become the research focus in the world.The grid faults in real operation can cause the generator disconnect from the grid and give rise to an enlarged fault resulting in a severely negative effect to restoring stabilized operation of grid,and it has seriously affected the security and stability of the grid system.So the study of low-voltage ride through(LVRT)has become a key reseach point at home and abroad.In this paper,on the basis of conventional control strategy of D-PMSG wind power system,we propose an improved control strategy that is suitable for low voltage ride through.This paper describes the current development of wind power technology,then describes the importance of the low voltage ride through fo wind power system and the research status at home and abroad.The paper introduced several commonly used methods of LVRT and the characteristics also with dynamics of wind turbines.After that,the paper established mathematical model of the direct-drive wind power system,including the permanent magnet synchronous motor,the DC bus link,PWM converter,which lay the foundation for the study of direct drive permanent magnet wind power system control strategy.Second,in this paper,the conventional control strategy and improved control strategy of the direct drive permanent magnet wind power system has been carried on the detailed analysis respectively.The generator-side converter and the grid-side converter control stratrgies have a detailed description and contrast.The improved control stratrgy equals the generator to power grid,use the generator-side converter to control the UC-link voltage and the stator voltage stability,and the grid-side converter to control the active and reactive power.In addition,the paper also introduced the low voltage droping and LVRT,compared the currnt focus LVRT methods.When power drops,the improved control strategy used the generator-side converter to maintain the DC bus voltage stability,restore stabilization of current on grid side,make sure the system's normal operation,greatly improved the safety and stability of wind power generation system.Finally,in order to verify the feasibility and reliability of the improved control stategy of direct-drive permanent magnet wind power system,as well as its application in LVRT,several simulation and experiment study has been done.Then the paper analysis and compared the results.Improved control strategy during normal operation,the wind power system has quickly respond speed,good dynamic performance,the DC bus voltage has small overshoot.but when the system reached steady state,the DC bus voltage has slight flutuations,lower stability than the conventional control strategy.When the grid voltage drop,compared to the conventional control strategy,the improved control strategy can maintain the DC bus voltage stability better,suppress oscillation of 2 times frequency,make sure the quick stability of the DC bus voltage and surrent,so that the direct drive permanent magnet wind power system can run normally during the grid falls.The feasibility&advantage of the presented strategy has been verified by simulations and experiments.