Short-circuit current of doubly fed induction generator under partial and asymmetrical voltage drop

The doubly fed wind turbine is the main equipment of wind generators. The fault transient characteristics of doubly fed induction generators (DFIG) have elicited the attention of many scholars. However, the short-circuit current (SCC) of power grid-contained DFIG under asymmetrical voltage drop cannot be accurately analyzed. The main difficulty is that the response and coupling of converters under partial voltage drop remain unclear. Thus, this paper presents an imperative study on SCC of DFIG, with particular attention to the transfer of negative-sequence voltage in the windings and rotor-side converter. The electromagnetic process and excitation control are simultaneously deduced in a uniform coordinate space by constructing positive- and negative-sequence vector models. The generating mechanism and analytical expressions of stator SCC are proposed. The positive- and negative-sequence equivalent models of DFIG during fault initial stage and steady-state process are constructed for practical short-circuit calculation. Simulation and physical testing are implemented to verify the theoretical analysis.