Low voltage ride-through enhancement of DFIG-based wind turbine using {DC} link switchable resistive type fault current limiter

Doubly-fed induction generator (DFIG)-based wind turbines utilise small-scale voltage sourced converters with a limited overcurrent withstand capability, which makes the DFIG-based wind turbines very vulnerable to grid faults. Often, modern {DFIG} systems employ a crowbar protection at the rotor circuit to protect the rotor side converter (RSC) during grid faults. This method converts the {DFIG} to a squirrel cage induction generator, which does not comply with the new grid codes. The recent grid codes need wind turbines to stay connected to the utility grid during and after power system faults, especially in high penetration level of wind power. Furthermore, the crowbar switch is expensive. This paper proposes a novel DC-link switchable resistive-type fault current limiter (SRFCL) to improve the {LVRT} capability of the DFIG. The proposed {SRFCL} is employed in the {DC} side of the RSC. The {SRFCL} solves crowbar protection activation problems and eliminates subsequent complications in the {DFIG} system. The proposed {SRFCL} does not have any significant impact on the overall performance of the {DFIG} during normal operation. Whenever the fault, whether symmetrical or asymmetrical, occurs, the {SRFCL} not only limits rotor over-currents but also prevents rotor speed acceleration and restricts high torque oscillations even during zero grid voltage, as recommended by some grid codes. To prove the effective operation of the {SRFCL} on the {RSC} fault current limitation, analytical analysis is performed in each switching interval. The proposed approach is compared with the crowbar-based protection method. Simulation studies are carried out in PSCAD/EMTDC software. In addition, a prototype is provided to demonstrate the main concept of the proposed approach.