Research On Broadband Oscillation Impedance Analysis And Stability Control Of Wind Power Grid System

As the installed capacity of wind power in the grid increases year by year,reports of wide-band oscillation accidents in wind power grid-connected systems have attracted widespread attention.In order to improve the safety and consumption capacity of large-scale wind power grid connection,this paper takes wind power series / parallel compensation grid connection system as the main research object,the broadband oscillation mechanism and main influencing factors were analyzed,and the control method based on virtual impedance application of wide-band oscillation suppression in grid-connected systems was studied.The specific research contents are as follows:Firstly,the impedance model of the wind power grid-connected system is derived.Mathematical modeling of DFIG based on the working principle,and deducing the equivalent impedance model of DFIG.The impedance model mainly includes three parts: induction generator,control system and grid-connected line.The control system model includes the current inner loop,the active power outer loop,the AC voltage amplitude outer loop and the phase-locked loop,and the grid-connected line considers two types of series compensation and parallel compensation.Secondly,based on the impedance model of the wind power grid-connected system,its broadband oscillation mechanism and influencing factors are analyzed.First,build a time-domain simulation model of the wind power grid-connected system in the PSCAD environment,and analyze the effects of wind speed,number of wind turbines connected to the grid,line parameters and control parameters on the system damping ratio.Then customize the impedance analysis program of the wind power grid-connected system in the Matlab environment to further calculate the system oscillation frequency under the influence of the aforementioned main parameters.Finally,according to the Nyquist stability criterion,the influence of the aforementioned main parameters on the system stability is judged.Thirdly,a virtual impedance control method suitable for suppressing wide-band oscillation of grid-connected DFIG systems.This method aims at the resonance mechanism of the wind turbines in different grid connection modes,and proposes to add virtual impedances to the stator and grid side control links of the DFIG,respectively.Among them,it is proposed to add virtual resistance on the stator side of the wind turbine to change the equivalent impedance amplitudeand phase angle for the SSR oscillation phenomenon of the wind power grid connection system.For the HFR oscillation phenomenon,a virtual impedance is added on the grid side of the grid-connected system to change its equivalent impedance amplitude and phase angle to achieve a wide-band oscillation effect.Finally,according to the Nyquist stability criterion to judge the stability of the system after the suppression strategy is added.Finally,a fully digital real-time simulation platform for DFIG-connected broadband oscillations under the Hypersim environment.Simulate the system sub-synchronous resonance and high-frequency resonance phenomena under adverse conditions of wind speed,number of DFIG connected to the grid,line parameters and control parameters,respectively.Calculate the current waveform at the grid connection point of the wind power system before and after the suppression strategy is added,and analyze the component content in the oscillation frequency band by FFT to verify the implementation effect of the suppression strategy.