Analysis on transient equivalent circuit of doubly fed induction generator with crowbar protection

摘要

In this paper, the forms of positive and negative sequence transient equivalent circuits (TECs) of doubly fed induction generator (DFIG) are derived and the constitution of them is analyzed in allusion to the typical condition that the crowbar circuit is activated under asymmetrical failure. It is pointed that the positive sequence TEC of DFIG is in the form of controlled voltage source connected in series with constant-value impedance, which is different from traditional synchronous generator. The transient equivalent potential (TEP) is alternating and damped with time and presents the feature of rapid variation, the extent of which is aggravated along with the increase of slip and crowbar resistance. The negative sequence TEC is in the form of single impedance which is time-invariant and the value is related to slip and crowbar resistance. The validity of theoretic evaluation is verified by simulation based on Matlab/Simulink, which provides scientific basis for further study of transient equivalence of single DFIG as well as the whole wind farm.