Research On The Key Techniques Of Wind Power Grid Low Frequency Oscillation Phenomena Mechanism And Suppression Method

Wind power occupies quite much proportion in distributed new energy power generation because of the advantages of no pollution,large reserves and regeneration.With wind power capacity and the installed capacity becoming more and more large,more and more wind farms have combined to the grid.Large-scale wind power grid has affected the stability of power system,especially the doubly fed induction generator(DFIG)operation is likely to lead to low frequency oscillation phenomena.The frequency,phase and amplitude of DFIG rotor current are controlled by the PWM converter to adjust the stator side power output.This structure does not isolate DFIG and power grid completely,which makes the whole system stability lowerable and may lead to low frequency oscillation phenomenon.The project studies mechanism and inhibition method of low frequency oscillation phenomenon.First of all,the project studies characteristics and harm of the low frequency oscillation phenomenon in domestic and foreign.Wind turbine,shaft,pitch control linear state models are established to study mechanism and suppression method of low frequency oscillation phenomenon in the MATLAB/simulink environment.DFIG,PWM converter and its control system are derived in detail in the synchronous rotating reference frame to get linear state model.Then,the project expounds the eigenvalues analysis method of the DFIG low-frequency oscillation phenomenon and analyses of the influence of wind power grid capacity and wind speed to clarify the mechanism of DFIG low-frequency oscillation phenomenon.The two-area-four-machine power system is simulated in MATLAB/simulink environment for demonstrating negative damping mechanism of DFIG low-frequency oscillation phenomenon.Finally,DFIG rotor side additional damping control link are designed based on the theory of Prony method and the automatic control.The link takes the slip of DFIG as the input signal.The output feedback access the inverter to compensate the system damping.The additional damping control link of two-area-four-machine power system is analysed byeigenvalue analysis and time domain simulation to verify effectiveness of the method.