Research On DFIG Low Voltage Ride Through Under Unbalanced Voltage

The development of new energy sources is changing with each passing day,and the direction of wind power grid integration is particularly rapid.In this paper,the Doubly-Fed Induction Generator(DFIG)grid-connected system is studied.Because DFIG has the characteristics of direct grid connection on the stator side,it is sensitive to the voltage drop of the grid when the system is running.Therefore,it must have Low Voltage Ride Through(LVRT)capability.For the DFIG low voltage ride through under unbalanced voltage,the main work of this paper is as follows:An DFIG low voltage ride through control scheme based on Fuzzy Active Disturbance Rejection Control(Fuzzy-ADRC)is proposed.Based on the mathematical model in the positive and negative sequence synchronous rotating coordinate system and the auto disturbance rejection control theory,this scheme is designed to design a fuzzy auto-disturbance controller suitable for DFIG low voltage ride through.For the Nonlinear State Error Feed-back(NLSEF)in the controller,the fuzzy logic operation part is introduced to enable the control system to modify the controller parameters online.The rotor-side control system based on fuzzy auto-disturbance is constructed to solve the problem of rotor-side current imbalance and active power and electromagnetic torque fluctuation during low voltage ride through.An improved dual-loop DFIG low voltage ride through control scheme is proposed.According to the control of the grid side part,the scheme designs two control targets and derives corresponding current commands according to the mathematical model and control requirements of the grid side converter.The BP neural network PID controller is designed to improve the flexibility of the voltage control link.In order to simplify the control structure,the current command value is transformed into a two-phase stationary coordinate system combined with an improved Proportion Resonant(PR)controller to achieve simultaneous positive and negative sequence control of the current portion.Therefore,an improved double-loop network side control system is constructed to solve the problem that the DC bus voltage fluctuation is too large and the AC side current contains negative sequence components during low voltage ride through.Finally,in the MATLAB/Simulink environment,the simulation comparison and analysis with the traditional control scheme proves the feasibility and superiority of the proposed scheme.