Evaluation of the Performance of a DC-Link Brake Chopper as a DFIG Low-Voltage Fault-Ride-Through Device

The performance of the doubly fed induction generator (DFIG) during grid faults is attracting much interest due to the proliferation of wind turbines that employ this technology. International grid codes specify that the generator must exhibit a fault-ride-through (FRT) capability by remaining connected and contributing to network stability during a fault. Many DFIG systems employ a rotor circuit crowbar to protect the rotor converter during a fault. Although this works well to protect the generator, it does not provide favorable grid support behavior. This paper describes an experimental investigation of an alternative FRT approach using a brake chopper circuit across the converter dc link to ensure that the dc-link voltage remains under control during a fault. Two different approaches to chopper control are examined and the resulting FRT performance is compared with that of a conventional crowbar approach. The new chopper-based control methods are experimentally evaluated using a 7.5-kW DFIG test rig facility.