Enhanced Fault Ride-through Scheme for Mitigating Rotor Speed Instability of Doubly Fed Induction Generator Based Wind Farms

摘要

This paper analyzes and proposes a novel scheme with suitable control strategy to increase the probability of successful fault ride-through (FRT) as well as to enhance the rotor speed stability of doubly fed induction generator (DFIG) based wind farms. The proposed FRT scheme consists of an uncontrolled rectifier, two sets of IGBT switches, a diode and an inductor connected between the rotor circuit and dc link capacitor, in parallel with the rotor side converter of DFIG. In the proposed scheme, during a fault event, the input mechanical energy of the wind turbine is stored as electromagnetic energy in the inductor. Consequently, torque balance between the electrical and mechanical quantities is maintained and the rotor speed deviation is thereby reduced. This results in reduced reactive power requirement and rapid reestablishment of terminal voltage on fault clearance. Moreover, the stored electromagnetic energy in the inductor is transferred into the dc link capacitor on fault clearance; thereby relieving the grid side converter from charging the dc link capacitor. The proposed FRT scheme is validated through an extensive time domain simulation study employing PSCAD/EMTDC software. Simulation results demonstrate the effectiveness of the proposed FRT scheme in achieving successful fault ride-through and rotor speed stability of DFIG based wind farms.