Research On Transmission Chain Module And Damping Optimization Control Of Doubly Fed Induction Generator Under Voltage Drop

With the development and utilization of wind energy,the share of wind power in the power grid is increasing year by year,while the General Administration of China has more stringent requirements on the low-voltage ride-through performance of wind turbines,and the technical requirements for grid-connected operation of wind turbines are getting higher and higher.In view of the grid-connected operation of doubly-fed wind turbines under low voltage crossing,it is of great significance to study the dynamic response characteristics of the transmission chain of the wind turbines under voltage sag for guaranteeing the operation safety of the doubly-fed wind turbines and the power grid.Based on the current situation of related studies both at home and abroad and the analysis of the basic characteristics of doubly-fed wind turbines,the mathematical model of doubly-fed wind turbines and the transmission chain model of doubly-fed wind turbines are established in this paper.Two or three or four or five mass blocks are set up.Based on PSCAD platform,the drive chain module is modeled and simulated,and the dynamic response characteristics of doubly-fed wind turbine under grid voltage sag are analyzed.The simulation results of different voltage sag depths show that the greater the voltage sag depth is,the larger the amplitude of the fluctuation excited by the drive chain will be,and the longer the time will be needed to restore the balance value.The simulation results of different mass block models under the same drop degree show that different equivalent models of transmission chain will affect the transient simulation operation of grid-connected doubly-fed wind turbine,and the equivalent five mass block equivalent model can more accurately reflect the mechanical and electrical transient characteristics of doubly-fed machine.In terms of the low frequency damping oscillation after voltage fault,the damping control of doubly fed fan is studied.The existing active and reactive power damping control schemes are analyzed and summarized.Considering the capacity limitation of the doubly fed fan converter,a damping controller is designed to meet the reactive power support during the fault traversing period.The low frequency oscillation of power system can be damped under the circumstance of satisfying reactive power injection current.On the basis of this controller,a coordinated control strategy of low voltage traversing control,damping control and nonlinear PI pitch control is proposed.Active damping control is added to the recovery process of low voltage traversing.Finally,the simulation results of DIgSILENT/Power Factory show that this coordinated control can be very good in reducing the power oscillation of the power system when compared with the traditional control strategy,which proves the effectiveness of the strategy.