An analytical method for the response of DFIG under voltage dips

Electromagnetic transients resulting from voltage dips complicate the low-voltage ride-through (LVRT) of doubly fed induction generator (DFIG) based wind turbines (WTs). To study the transients deeply, an analytical method to solve the dynamic response is presented in this paper. Although some attempts have been made in literature, the accuracy cannot be ensured, or the physical significance implied in the transients is not feasible to be revealed without a proper method to this complex process. To clarify the response, a concept of equivalent fault source is defined in the stator and rotor circuit respectively and the overall behavior is decomposed into a stator-fault-sourced response and a rotor-fault-sourced response. The former corresponds to the dips of the stator voltage, while the latter deals with the variations in the rotor resistance and the terminal voltage due to activation of the crowbar. Adding these two zero-state responses to the healthy pre-fault conditions, the overall response can be constructed accurately and each of the terms has its apparent significance. With the analytical solution, the behavior is discussed and some important features are presented. The accuracy of the solution is verified by close agreement with the simulative results from a MATLAB/Simulink model of a 2MW DFIG and the experimental records on an 11kW laboratory-scale test rig.