Abstract:
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The aim of this paper is to analyze the dynamic behavior
of the doubly fed induction generator (DFIG) subject to
symmetrical voltage sags caused by three-phase faults. A simple
control algorithm is considered and assumed ideal: the rotor current
irf in the synchronous reference frame is kept constant. This
hypothesis allows the electrical transient to be solved analytically,
providing a comprehensive description of DFIG behavior under
symmetrical sags. The fault-clearing physics of symmetrical sags is
also analyzed. That is, the fault is cleared in the successive natural
fault-current zeros, leading to a voltage recovery in one, two, or
three steps. This clearing process, called discrete fault clearing in
this paper, results in a more accurate sag modeling than the abrupt
or instantaneous fault clearing (the usual modeling in the literature).
The fault-clearing process has a strong influence on the rotor
voltage required to control the rotor current after fault clearing. To
compare the effects of both abrupt and discrete sags, different wind
turbine (WT) operating points, which determine different generated
powers, are considered. This study helps in the understanding
of WT fault ride-through capability. |