Stability Analysis And Rearch On Control Strategy Of Double-fed Induction Generators Under Weak Grid Fault

In recent years,with the rapid development of the wind power industry,the penetration of wind power generation system into the power grid has been deepening.In order to ensure the stability of the power system,countries have formulated strict low-voltage crossing and grid-connection criteria for wind power generation system.In addition,wind turbines under weak grid conditions are more prone to instability when they fail,so there is a risk that the typical LVRT control strategy may not work for wind turbines.Therefore,this paper mainly takes doubly-fed wind turbine under weak grid fault as the research object,conducts a comprehensive analysis of the system dynamic stability of doubly-fed wind turbine with the combination of small signal analysis method,and proposes several corresponding solutions to the system stability under weak power grid fault.The specific work contents are as follows:(1)The small signal state space model of double-fed wind turbine under weak grid is calculated with the small signal state space analysis method,and the coupling relationship between each link of DFIG system is explored in detail.(2)Based on the state space model of small signal of doubly-fed wind turbine,the influence of each leading parameter on the stability of small signal of DFIG system is further explored.Among them,weak power grid,high rotor speed and deep voltage drop may cause the system's small signal instability.By reducing the rotor current loop bandwidth,reducing the PLL bandwidth and injecting reasonable active current,the stability of small signal in the LVRT process of DFIG system can be effectively improved.(3)The influence of leading parameters on the stability of small signal of DFIG system is verified by simulation analysis.Meanwhile,the simulation results also show that the PLL bandwidth and the rotor current loop bandwidth should be reasonably selected,which can not only effectively improve the system stability but also guarantee the dynamic response performance of the system.(4)Aiming at the stability of DFIG system under weak power grid fault condition,four control strategies are proposed.Among them,Crowbar resistance with a higher resistance value within a reasonable range can effectively reduce power oscillation and improve the voltage stability of the system.The optimal current proportional control strategy,frequency damping control strategy and voltage integral feedforward strategy can significantly improve the system's small signal stability.(5)The four proposed control schemes are simulated and verified in detail on MATLAB/Simulink platform and 11kW doubly-fed wind turbine experimental platform,and the reliability and effectiveness of the proposed control scheme are proved.