Analysis Of Dynamic Characteristics Of Wind Turbine Drive Train Under Voltage Sag

With the increasing of air pollution,the development and utilization of wind energy is becoming more and more important in the country's energy strategy.The proportion of wind turbine in power grid is becoming larger and larger.And the national grid puts forward the characteristics of low voltage ride through.The security and stability of wind turbine is facing new challenges.Under the condition of low voltage ride through doubly fed wind power generator group electrical coupling problem,we study the dynamic response characteristics of wind turbine drive train.It is of great significance to ensure the safety of wind turbine and power system.In order to accurately explore the electromechanical coupling effect of grid connected doubly fed wind turbine.Firstly,we analyze the basic characteristics of wind turbine and established mathematical model of wind generator and drive chain and double fed induction generator.When modeling the drive train,considering the flexibility of the drive shaft between the wind turbine and the generator,we establish the two and three and four and five mass models.Further more,we expound the DFIG under stationary coordinates and in the rotating coordinate system model,and analyze the relationship between the running status and the power of double fed induction generator,and then describes the relationship between the DFIG operation state and power.We are based on the PSCAD platform for modeling and simulation.We establish the simulation model of 1.5MW DFIG generator-power-net under different mass block partition conditions.We analyze the effect of voltage drop on the oscillation of the drive train from the three factors of stiffness coefficient,mutual damping and self damping.The simulation results show that the smaller the stiffness coefficient is,the more intense the vibration is,the greater the damping vibration amplitude is,the greater the self damping is,the lower the transmission efficiency is.The drive train which is equivalent to the five mass block model can more accurately reflect the dynamic characteristics of the system.Finally,we analyze the dynamic response characteristics of DFIG under the grid voltage drop.The simulation analysis of different voltage sag depth shows that the greater the voltage sag depth,the greater the vibration amplitude of the drive chain,and the time required to return to the equilibrium value.The results of different mass block models under the same condition of dropping degree show that different models of drive train of the doubly fed induction generator has little effect on the dynamic of the reactive power,but it has a great influence on the torque and speed etc.