A Simple Multifunctional DC Chopper for Fault Ride-Through Capacity Enhancement of a DFIG

Generally, crowbar circuits and DC choppers are employed to prevent rotor-side converter overcurrent and DClink overvoltage, respectively, during the fault ride-through (FRT) process in doubly fed induction generators (DFIGs). However, once the crowbar is activated, the DFIG cannot fulfill the grid code requirements. This letter introduces a multifunctional DC chopper that can operate in current-limiting and voltage-limiting modes without requiring a crowbar, thereby avoiding RSC blocking. The proposed design is simple and facilitates the implementation of nonlinear control. Hardware-in-the-loop tests performed on a real-time digital power system simulator show that the proposed scheme suppresses both the DC-link voltage and rotor current under severe faults and provides better transient performance. This outcome not only enhances the FRT capability of DFIGs but also advances FRT research into renewable energy systems with grid-connected inverters.