Protection algorithm for the windings of a doubly-fed induction generator using the d-q equivalent circuits

A doubly-fed induction generator (DFIG) system is being applied to the modern wind turbines, because it has many advantages such as the variable-speed operation, relatively high efficiency and the small converter size. This paper proposes a protection algorithm for a DFIG based on the d-q equivalent circuit in the time domain. In the DFIG, the voltages and currents of the rotor the stator side are available. The proposed algorithm estimates the instantaneous induced voltages using the voltages and currents of the rotor and the stator side. If the difference between the two estimated induced voltages exceeds the threshold, the proposed algorithm detects the internal fault. The performance of the proposed algorithm is validated under various operating and fault conditions using PSCAD/EMTDC.