Research On Sub-synchronous Resonance Caused By Grid-Integration Of Doubly Fed Wind Power Generation System Via Series Compensated Lines

Wind power and series-compensation transmission system can improve the capacity of the transmission,which is widely used in the world at present.However,there is a risk of sub-synchronous resonance(SSR)in the wind power system.In recent years,many SSR accidents occurred in power systems with DFIG and series-compensated lines.In the process of sub-synchronous resonance,a large number of doubly fed induction generators(DFIGs)will cause protective action due to the unbalanced current.It would seriously weaken the safe and reliable operation of the wind farms as well as the whole power system.Therefore,the phenomenon of SSR caused by wind-series compensation system has aroused widespread concern of domestic and foreign scholars.In this paper,according to the SSR problem caused by wind power and series-compensation system in Guyuan,the equivalent model of wind farms and series-compensated power system in Guyuan is built according to the actual parameters.Based on this model,the small-signal model of DFIG and series-compensated transmission system is built and the system stability criterion is derived.Then,the equivalent model of wind farms and series-compensated power system in Guyuan is built in the simulation platform.Based on that model,the SSR characteristics of wind farms in Guyuan area under different DFIG numbers,wind speed and line parameters are investigated through impedance method.Finally,this paper presents two kinds of SSR suppression measures.One is to change the line parameters,by destroying the resonant circuit to achieve the purpose of inhibiting SSR;the other is to add an SSR suppression filter on the DFIG rotor side converter control.The SSR suppression filter is embedded in the feedback control and the SSR mode signal in the current feedback signal is filtered to avoid the risk of SSR in the series-compensation system.The effectiveness of the suppression measure is verified by simulation.