Research On Influence Of High Penetration Wind Power Grid Integration

With the gradual depletion of traditional fossil energy sources and the growing problem of environmental pollution,wind power integration technology have developed rapidly in the world.Due to the gradual increase of wind power penetration rate,the impact of large-scale wind power on the safe and stable operation of power systems is becoming more and more prominent.At present,the impact analysis of wind power generation for accessing to the power grid at home and abroad is mostly based on strong power grid scenario.This thesis studies the wind power impact on the power grid under the scenario of relatively high wind power penetration rate and relatively weak power grid.The main work includes:(1)This thesis introduces the structure and mathematical model of doubly-fed induction generator(DFIG)and permanent magnet synchronous generator(PMSG).According to the mathematical model of the wind turbine,the principle of vector decoupling control of wind turbine is analyzed,and the control principles of rotor side(generator side)rectifier and grid side inverter of two wind turbines are analyzed.Then,this thesis establishes the model of wind speed,blade and transmission part,and introduces how the speed control and power control of variable pitch variable speed wind turbine control the speed and pitch angle to achieve the Maximum Power Tracking of wind energy.An electromechanical transient simulation model of doubly-fed induction generator and permanent magnet synchronous generator is established in the power system simulation software DIgSILENT/Powerfactory.(2)The static voltage stability analysis of power system is carried out by PV curve method,VQ curve method and sensitivity analysis method.Based on DIgSILENT/Powerfactory,a 4-machine 9-node system with equivalent doubly-fed induction generator wind farm was built.The influence of DFIG on the static voltage stability of power system under different electrical distances and different wind power penetration rates was studied.The simulation analysis shows that the increase of the transmission line length between the wind farm and the main power grid will reduce the static voltage stability of the system.The increase of wind power permeability will make the static voltage stability and active load margin first increase and then decrease,while the reactive load margin will decrease.(3)Time domain simulation method is used to analyze the transient voltage stability of power system.It is found that the increase of wind power penetration increases the voltage support of grid-connected points,but the voltage recovery time increases and the fluctuation range increases,and it is verified by simulation.The thesis also analyzes the occurrence of the same type of fault at different locations on the transmission line and the use of different types of wind turbines.The results show that the transient voltage stability of the wind farm's grid-connected point increases when the fault point is far away from the wind turbine.Power grid with PMSG have better transient voltage stability than power grid with DFIG.(4)Analysis of the interaction between multiple wind turbines in a wind farm.The wind turbines of the wind farm are coupled to each other through the grid,and the wind turbines interact with each other.The research shows that the steady-state characteristics of the wind farm using the single-machine aggregation model are basically the same as those of the real wind farm,but the transient characteristics of the single-machine aggregation model are quite different from the actual wind farm,indicating that the transient output characteristics of the wind farm are affected by the wind turbine.Mutual influence is greater.At the same time,in the high-permeability wind power system,the interaction between wind turbines cannot be ignored.Therefore,for wind farm transient characteristics and wind power high permeability system analysis,multi-machine model should be adopted.This thesis proposes a multi-machine clustering algorithm to select the minimum fan cluster number in the case of high permeability.