Sensorless Doubly-Fed Induction Generator Control Under Power System Transients and Faults: The Influence of Magnetic Saturation

The present paper investigates the influence of magnetic saturation on the rotor position and speed estimators and the machine behavior during transients and short-circuit faults for a doubly-fed induction generator (DFIG) connected to the power grid. The DFIG is considered driven by a wind turbine whose torque vs. generator speed at different wind speed is optimised. The DFIG is connected to the grid, at a certain initial speed, simultaneously in the stator and in the rotor for given values of active and reactive stator power references. Subsequently a sudden three-phase short-circuit at the middle of a typical local power grid is investigated. A computer program in Matlab-Simulink package for the whole system has been developed and applied to simulate transients as described above with and without considering the magnetic saturation in the machine. It is shown by digital simulations that during short-circuit the sensorless control fails without considering the magnetic saturation and even during the sudden connection to the grid the errors in position and speed estimation and in the transient description are notable.