Research On Small Signal Stability Analysis And Control Strategy Of PMSG-based Wind Turbines Under Asymmetric Grid

With the introduction of policies related to the global environment and national adjustment,the development space of wind power industry in China and even around the world has become more and more broad.The proportion of wind power units in the power grid has increased significantly,and the influence of wind power units on the stability of the power system,especially the terminal power grid in remote areas,has become increasingly significant.For this reason,major wind power countries in the world have issued grid-connection guidelines to make clear requirements on the operation reliability of wind power units.Among them,the grid-connection guidelines on the behavior of wind turbines under the condition of grid failure is recognized as a severe challenge to wind turbines,which not only requires wind turbines to be able to adapt to all kinds of grid failures,but also requires them to have the ability to support the recovery of the fault grid.When the grid impedance content is high,the symmetrical/asymmetrical sag fault of grid voltage has the most significant influence on the stability of wind turbine,and the negative sequence component generated by the asymmetric fault is more likely to have coupling effect with the grid impedance.Therefore,it is very important for theoretical research and engineering application value to study the operation characteristics of grid-connected wind turbines under such grid faults and put forward the corresponding control measures.In this background,this article to permanent magnet synchronous generator(PMSG)based wind turbine as the research object,the small-signal model as the core.By means of theoretical analysis,simulation research and experimental verification,the small-signal stability of PMSG based wind turbine with during asymmetric faults of the grid is studied deeply and systematically.Finally,an improved control strategy for grid-friendly wind turbine which can adapt to the grid code is proposed.The research focus of this paper is as follows: 1)Small-signal modeling and stability analysis of PMSG based wind turbine during asymmetric faults;2)Coordinated control operation strategy of converters at the machine side and the grid side of PMSG based wind turbine during asymmetric faults of the grid.In this paper,the PMSG system is modeled with small-signal based on mechanical vibration theory,and the small-signal mass-spring-damping model is established,and analyzed by stability criterion.Parameters such as regulator bandwidth,power grid line impedance and power grid voltage dip degree effect the stability of the system is given,explored the stability of the PMSG system during asymmetric faults,and design the machine side,grid side coordinated control strategy of the converter,the purpose is to make the PMSG system during the grid voltage dip fault can keep running stability,then verified by the simulation analysis and the effectiveness of the strategy.Finally,the corresponding PMSG hardware experimental platform was built,and the reliability and stability of the cooperative control strategy during the asymmetric faults period were verified by the experimental results.