Dynamic behavior of the excitation circuit of a doubly-fed induction generator under a symmetrical voltage drop

The large-scale application of doubly-fed wind turbines has significantly changed the fault transient characteristics of power systems. However, the transient state of a doubly-fed induction generator (DFIG) under large disturbances is difficult to accurately evaluate. The main difficulty lies in the failure to acquire the transient process of the DFIG excitation circuit because of the high orders and the strong coupling of excitation control. This paper presents a detailed transient analysis of a DFIG, with focus on the dynamic behavior and effects of the excitation circuit. The dynamic models of the rotor-side converter and the grid-side converter, which include the excitation regulation and the electromagnetic process, were constructed. The effects of the implementation of controllers on the transient behavior of the DFIG are analyzed by deducing the transitive relation of transient processes. Simplified expressions of DFIG electrical variables are proposed with the excitation regulation considered.