Research On Transient Stability And Control Strategy Of Grid-connected Wind Power Generation System

Vigorously developing new energy is the primary measure to accelerate the realization of "carbon neutralization" and "carbon peak".Wind energy has the advantages of easy development,rich reserves,high efficiency and cleanliness.It is the main force in China’s energy structure transformation,and has become a new energy with the highest proportion of grid connection.In recent years,the development of onshore wind power has begun to slow down,while offshore wind power has become the focus of China’s new energy installation field,all of which use high-capacity full-scale wind turbines.The full-scale wind power generation system is connected to the grid through voltage source converter（VSC）,so as to realize the flexible control of power.However,the grid-connected converter isolates the inertia of the generator.With the increasing proportion of wind power in grid,the inertia of the grid will be further lost,which may lead to the stability problem of power system.Therefore,it is necessary to deeply study the stability of grid-connected wind power generation system,reveal its instability mechanism,and put forward the corresponding control strategy,so as to provide a theoretical basis for realizing high proportion of wind power grid connection.At present,there have been relatively rich results in the research on the small signal stability of grid-connected wind power system,its analysis method has become systematic,and the instability mechanism is relatively clear.However,the transient（large signal）stability research of gridconnected wind power systems is slightly insufficient,and its analysis methods are relatively scarce,and the instability mechanism and nonlinear dynamic behavior are also extremely complicated.Therefore,this paper focuses on the transient stability mechanism and stability control strategy of the full-scale grid-connected wind power system.The main work is as follows:Firstly,the current research status of transient stability of grid-connected wind power systems is reviewed,including research methods,instability mechanisms and stability control strategies.The mathematical model of grid connected full-scale wind turbine is established,and the simulation model is established on the platform of MATLAB/Simulink.The simulation results under full wind conditions verify the correctness of the model.Subsequently,the grid fault equivalent circuit of the full-scale wind turbine is analyzed,the transient stability reduced order model of the grid-connected converter is established based on the time scale analysis method,and the influences of the equilibrium point and system parameters on the transient stability during the grid fault is analyzed in detail based on the equal-area criterion（EAC）,and verified by simulation.Then,the influence of active and reactive current injection on transient stability during grid fault is analyzed,the current injection boundary conditions to ensure transient stability during grid fault are derived,and three transient stability control strategies based on limited current injection are proposed.The simulation results verify the effectiveness of the proposed control strategy.Finally,the transient stability reduced order model of a single wind turbine in the full-scale wind farm is established,the instability mechanism of a single machine in the wind farm is revealed,the transient stability margin of each single machine in the wind farm is quantitatively analyzed,and the influence of the internal impedance of the wind farm on the transient stability of the single machine is qualitatively analyzed.The simulation results verify the correctness of the proposed transient stability margin and the transient stability influence of internal impedance.