Research On Subsynchronous Oscillation Of Double-fed Wind Farm

With the extensive utilization and development of wind energy,the penetration rate of wind power in the power system continues to increase.The randomness,uncertainty and intermittent nature of wind power itself,and the increasing number of power electronic converter applications after wind power connected to the power system,etc,may pose a threat to the safe and stable operation of the power system.Doubly-fed wind turbines have become one of the most widely used wind turbines because of its advantages,this paper analyzes the problem of subsynchronous oscillation of doubly-fed wind farm grid-connected systems.The main work is as follows:Firstly,the working principle,characteristics and structure of the doubly-fed wind power system are studied,the stability region of the subsynchronous oscillation of the doubly-fed fan is studied and the mathematical model of the mechanical dynamics of the doubly-fed wind turbine,the doubly-fed induction generator,the converter of the doubly-fed wind turbine and its control system,and the phase-locked loop,the series capacitor compensation lines are derived,which will lay the foundation for subsequent research.Secondly,the principle and algorithm flow of the eigenvalue analysis method are introduced,and the small signal model and state matrix of the doubly-fed wind power generation system are derived,the program of the eigenvalue analysis method is compiled in MATLAB,eigenvalue analysis was carried out in combination with specific examples,and modal identification was performed based on the participation factor and subsynchronous oscillation mechanism,and the accuracy and validity of the eigenvalue analysis results were verified by time-domain simulation by establishing a double-fed wind power grid-connected system model in PSCAD/EMTDC,and the influencing factors of the subsynchronous oscillation are studied using the eigenvalue analysis method and the time domain simulation method,which mainly include wind speed,series compensation,and rotor-side converter control parameters,grid-side converter control parameters,phase-locked loop controller parameters,etc.In addition,the interaction between the rotor-side converter’s inner loop proportionality factor and outer loop proportionality factor is also analyzed.Finally,the research is focused on the suppression measures of subsynchronous oscillation in the grid-connected system of the double-fed wind farm.An equivalent impedance model of a doubly-fed wind farm grid-connected system is established.Based on the model,a sub-synchronous oscillation suppression strategy based on virtual resistance is designed,and its suppression effect is verified by time domain simulation.In view of the limitations of virtual resistance control,a method of sub-synchronous oscillation suppression of virtual impedance control is proposed on the basis of virtual resistance control,and its effectiveness is verified by frequency sweep method and time domain simulation method;A sub-synchronous oscillation suppression method is proposed by installing a band-stop filter at the output of the rotor-side controller to absorb sub-synchronous frequency current.The validity of the method was verified by time domain simulation.Based on the rotor current component analysis,a sub-synchronous oscillation suppression strategy based on rotor current phase shift is proposed,and its strong sub-synchronous oscillation suppression effect is verified by time-domain simulation.