Impact Of DFIG-based Wind Farms Interconnected To Power Grid On Subsynchronous Oscillation Of Thermal Generator Set

Long-distance transmission technology,especially series compensation technology,has been widely applied in China due to the reversed distribution of power generation areas and load centers.Although series compensation technology can improve transmission efficiency,it brings the threat of subsynchronous oscillation to power system.With the development and use of wind resources,many subsynchronous oscillation accidents caused by grid-connected wind farm have happened at home and abroad.Therefore,it is of great practical significance to analyze the influence of grid-connected wind farm on subsynchronous oscillation.Considering that doubly fed induction generator(DFIG)is the main generator type of wind power generation in China,this paper analyzes and studies the influence of the grid-connected system of doubly-fed wind farm on the subsynchronous oscillation of thermal power units.According to the working principle and structure of turbine generator and doubly-fed induction generator,this paper establishes the mathematical models of turbo-generator set,doubly-fed wind generator set and series compensation line.Based on the PSCAD software,the time domain simulation model of the grid-connected system of doubly-fed wind farm is established and verified.The current classification,mechanism and main analysis methods of subsynchronous oscillation in power system is compared,and complex torque coefficient approach is determined as the main analysis method in this paper.Combined with the engineering practice,this paper expounds the concrete application method of the complex torque coefficient approach and the stability criterion in practical application.The change of the electrical damping of the system after the doubly-fed wind farm is connected to the grid is analyzed by using the test signal method.The affection of thermal power system parameters,wind farm parameters and doubly-fed fan control parameters on the grid-connected effect of the wind farm are studied,and the influence law of relevant parameters is obtained.Finally,the fault device and blocking filter are added into the simulation model and analyzed by time domain simulation.The simulation results further clarified the relationship between wind farm and system subsynchronous oscillation.