Online Identification And Suppression Of Sub-synchronous Oscillation In DFIG-based Wind Farms

Long-distance transmission of the wind resources and the electricity load in the reverse direction was a remarkable characteristic of China's wind power generation.In order to sent out the wind power in a better way,large scale and long distance wind power transmission mode was imperative.Series capacitor compensation device installation in the transmission line could effectively improved the long distance transmission capacity and the overall performance of the system.At the same time,sub-synchronous oscillation(SSO)of the power system would be more easily caused.Based on doubly fed induction generator(DFIG),this paper tried to analyze the problem of SSO caused by DFIG in series compensation capacitor circuit.Firstly,the mathematical model of DFIG-based wind farms was established according to the need of SSO in DFIG-based wind farms,including wind speed model,aerodynamic model,pitch angle control system model,rotor shafting model,DFIG model,converter control system model,and series compensation transmission line model.The established mathematical model laid a theoretical foundation for identification of the modal parameters for SSO and the presention of suppression measures.Secondly,identification of SSO parameters based on cubical smoothing algorithm with fivepoint approximation and auto-regressive moving average(ARMA)algorithm was proposed based on the measured signal of the wide area measurement system(WAMS),and the noise-like characteristics of the measured signal.Firstly,the signal of SSO was denoised by cubical smoothing algorithm with five-point approximation,and then,the denoised signals through establishing ARMA model to obtain the SSO modal parameter was identified.The proposed method was used to identify the ideal signal and the speed deviation signal of IEEE first benchmark model with doubly-fed wind farms.The results of compared with Prony algorithm and ARMA algorithm showed that the proposed method could correctly identify the dominant mode,and the identification relative error was lowest.Furthermore,the current measured signals on Tongyu wind farm in Jilin province was identified,and it was verified that this method was also applicable to the actual wind power system,and the result could provide accurate dominant modal parameters for the suppression of SSO.Finally,combined with the mathematical model characteristics of DFIG-based wind farms and the online identification results of the SSO mode,the strategy of the additional damping controller with reactive power ring to the rotor side was selected to suppressed SSO.The good inhibitory effect was demonstrated by the simulation results.In summary,for the problem of SSO in DFIG-based wind farms,the on-line identification and suppression of oscillation modal parameters were effectively butted and integrated.This method not only improves the accuracy of modal parameter identification,but it also realizes real time,fast and effective suppression of SSO.This paper has 38 figures,7 tables and 54 references.