SSO Mitigation Of Wind Turbine Using DFIG Based On Impedance Optimization Reshaping Under Variable Wind Conditions

In order to deal with the fossil energy crisis and environmental pollution,the new energy power generation technology represented by wind power generation is gradually replacing the traditional thermal power generation.However,with the increase of wind turbine capacity and the expansion of wind farm scale,the stable operation of power grid has been seriously affected.Since the beginning of the 21st century,grid-connected wind power system has experienced frequent sub-synchronous oscillation(SSO)accidents.In order to improve the ability of the system to cope with sub-synchronous oscillation,this paper takes the the doubly-fed wind power and series-compensated transmission system as the research target,establishes the impedance model of wind turbine using DFIG,analyzes the key factors that induce sub-synchronous oscillation.Considering the change of wind speed,a variable wind impedance optimization reshaping technology that can effectively mitigate the sub-synchronous oscillation is proposed.The specific research steps are as follows:Firstly,the doubly-fed wind power generator is divided into two parts:a GSC unit and a controlled DFIG unit.The frequency domain impedance models of GSC unit,controlled DFIG unit,transmission line and transformer are established based on three-phase static coordinate system,considering circuit topology,DFIG transient characteristics,converter control and dynamic response of phase-locked loop(PLL)to harmonics.The frequency domain small-signal impedance model of the system is formed according to serial and parallel circuits,which lays a theoretical foundation for identifying the dominant factors of oscillation and proposing mitigation strategy.Secondly,based on the impedance model of grid-connected wind turbine using DFIG,combined with the aggregate RLC stability criterion,wind speed variation and reasonable adjustment range of control parameters,a so called crossing sensitivity analysis method for variable wind conditions is proposed.The key factors inducing SSO of grid-connected wind turbine using DFIG are decided.The simulation model based on Matlab/Simulink platform verifies the correctness of the crossing sensitivity.Finally,according to the key influencing factors screened out through crossing sensitivity,a SSO mitigation strategy based on impedance optimization reshaping under variable wind conditions is further proposed,which is characterized by the applied parameter optimization and adjustment scheme adopting "off-line tabulation,real-time parameter adjustment",in which the additional control parameters are designed through particle swarm optimization(PSO)algorithm.The advantage of the strategy is that it can effectively achieve SSO mitigation under variable wind conditions.Time domain simulation experiments verify the effectiveness of the improved strategy.