Rcsearch On The Control Scheme To Damp DFIG-associated SSR On The Grid Side In Guyuan Wind Farnms

The scale of China's wind power industry is developing rapidly and the cumulative installed capacity has ranked top in the world.China's power grid now faces the risk of SSR due to the large-scale wind power generation.With the series complement operation in DFIG-based wind farms in Guyuan Hebei Province,there have been dozens of SSR problems caused by wind turbines and series compensation.This caused people to worry about the safety of new energy connecting to the grid.In this paper,the generation mechanism of SSR induced by DFIG is analyzed in-depth.A new grid-side suppression strategy is proposed for the SSR problems in Guyuan.Firstly,the structure of Guyuan wind farms and the characteristics of SSR in Guyuan area are introduced.The model of Guyuan wind farms is built on the simulation software Matlab/Simulink,which shows the SSR event.The mathematic model of the DFIG connected by fixed series compensation is studied in detail,which lays the foundation for further analysis.Secondly,the eigenvalue analysis method is used to analyze the influence of various factors on the SSR of the DFIG.The factors include the proportional parameters of the rotor side controller,the integral parameters of the rotor side controller and the transmission line parameters.Then,the generation process of SSR of DFIG is revealed.Based on the eigenvalue analysis,the equivalent impedance model of polymerization wind field is deduced.The mechanism of SSR in doubly-fed wind field is explained:an induction generator effect which is involved in the rotor side controller and is affected by the system operation mode at the same time.Last,aiming to solve the SSR problems in Guyuan wind farms,a new type of SSR damping strategy(SDS)based on current injection with positive damping characteristic was designed.SDS consumes only electrical energy at the sub-synchronous frequency without affecting the mains frequency.It is equivalent to purely resistive at the sub-synchronous frequency,and is equivalent to an open circuit at the mains frequency.Simulation results show that SDS has a better inhibitory effect.