| With the rapid development of wind power technology,the scale of wind power in the power grid is larger and larger,and security and stability problems brought about by it are more and more obvious.Among them,frequency resonance is one of the prominent problems.In this paper,high-frequency oscillation generated by grid-connected doubly-fed induction generator system is studied.Firstly,a simulation model for studying high-frequency resonance characteristics of grid-connected doubly-fed induction generator system is built in the Matlab/Simulink.Secondly,an impedance mo del of doubly-fed wind power system and grid-connected system is established by small-signal impedance method.The correctness of the simulation model and impedance modeling is verified by time domain simulation and frequency scanning.Then based on the simulation model and impedance model,influence of various factors on the high frequency resonance of doubly-fed wind power system is analyzed.Finally,oscillation suppression measures are proposed,and the simulation proves its effectiveness.The specific research contents of this paper are listed as follows.(1)A model for studying resonance characteristics of grid-connected doubly-fed induction generator system is built in Matlab/Simulink.The dominant high harmonic frequency and harmonic content are obtained by time domain simulation and Fast Fourier Transform(FFT),which reproduces high-frequency resonance of a wind farm in South China,which verifies the correctness of the simulation model.(2)Based on the simulation model of grid-connected doubly-fed induction generator system built in Matlab/Simulink,the corresponding impedance model is established.Bode plot of impedance is drawn by frequency scanning method and compared with time domain simulation,verifying correctness of the impedance model.(3)Based on the impedance model of grid-connected doubly-fed induction generator system,the effects of grid-connected capacity,grid-side filter,control parameters,phase-locked loop,electrical distance,electrical strength and other factors on high-frequency oscillation are analyzed.The conclusion is drawn that electrical distance is the most important factor affecting the resonance of the system.The influence of other factors is relatively small,and the influence of control parameters on high-frequency resonance characteristics of the system is negligible.When electrical distance increases,high-frequency resonant increases significantly,frequency of high-frequency resonant gradually decreases,the overall harmonic content gradually increases,and harmonic content at the resonant frequency also gradually increases,deteriorating the power quality.Based on analysis of influencing factors of high frequency oscillation in grid-connected doubly-fed induction generator system,high-frequency oscillation suppression method of second-order band-stop filter and based on switching capacitance are proposed.The effectiveness of the improved frequency oscillation suppression method in this paper is proved by simulation. |
