Power Oscillation Analysis Of Large-scale Wind Power Delivery System

Recently,wind energy has been extensively used as a clean energy source.In China,the characteristics of large-scale centralized development of wind power and high voltage long-distance transportation make series compensation technology widely used.However,the cascade compensation system may bring the risk of sub-synchronous oscillation(SSO)to the operation of the power grid,and even cause the large-scale wind farm separated from the power grid and the generator's inter circuit damaged.Based on this situation,this paper studied the problem of the sub-synchronous oscillation of the double-fed induction generator(DFIG)-based wind farm which connected to the grid system by series compensation.First of all,the mechanism,analysis methods and suppression measures of the sub-synchronous oscillation were analyzed during the large-scale wind power centralized grids connected to the national grid.With the help of PSCAD software,a DFIG-based wind farm simulation model with one double-fed induction generator,two double-fed induction generators or three double-fed induction generators as the research objects were established.In addition,two sub-synchronous oscillation suppression measures and the design method of the damping controllers were proposed based on the strategy of additional damping control and the method of stator and rotor torque analysis.One is the parallel damping controller.The filter and phase shift link are added to the active and reactive loops of the rotor side converter.The other is the series damping controller,which modifies the fan control system.The phase shift is added to the reactive loop of the rotor side converter and sub-synchronous oscillation is suppressed by modifying parameters.In result,the effectiveness of the proposed suppression measures was verified by the DFIG simulation model.At last,based on the operation and maintenance requirements of the DFIG-based wind farm,a strategy was proposed to suppress SSO of the wind farm by adding damping controllers to wind turbines in a certain proportion instead of all units.The suppression method can suppress the sub-synchronous oscillation of the wind farm.Aiming at the parallel damping controller and series damping controller,the equivalent two and three machine models of the DFIG-based wind farm were established,and the proposed strategy was verified.This study can provide reference for operation analysis of large-scale wind power grid and design of DFIG control system.