Analysis and Improving FRT Capability of Grid Connected Doubly Fed Induction Generator based Wind Turbines

This thesis deals with the analysis, modeling, and control of the doubly-fed induction generator (DFIG) based wind turbines (WTs) and fault ride through capability improvement (FRT). The aim of FRT improvement is based on grid codes during faults WTs rather than disconnecting from grid, it has ability to support grid by injecting reactive current. Different FRT improvement methods are studied with objective of injecting demagnetizing and transient currents during fault. During the fault DFIG rotor back electromotive force (EMF), is high causing high rotor currents. It is found that transient reconfiguration solution and coordinating control strategy for power converters to enhance FRT and transient voltage support capability of a DFIG. It is found that feed forward terms in current controller of rotor side converter reduce steady state error during tracking. In transient reconfiguration during fault grid side converter comes in parallel with rotor side converter to share high rotor currents. A coordinated demagnetizing and reactive current control strategy with feed forward terms in controller designed for converters during transient conditions. The response of the DFIG wind turbine system with transient reconfiguration and coordinated power converter control to grid disturbances is simulated using MATLAB/Simulink®. Keywords: Doubly-fed induction generator, wind turbine, Fault ride through, Grid codes, transient reconfiguration, coordinated power converters control