LVRT performance limit of DFIG with traditional AC crowbar and DC-link brake approach

Doubly Fed Induction Generator (DFIG) system is subject to high transient voltage at rotor side when there is voltage sag at stator/grid side, which is beyond the capability of rotor side converter to handle. Traditional approach is to apply crowbar circuit to shunt the transient rotor current from the rotor side converter. DC-link brake is also typically applied to suppress the rise in DC bus voltage. This paper discusses the transient process and pointes out the performance limit for low voltage ride through (LVRT) with the traditional AC crowbar + DC-link brake approach. Both balanced and unbalanced grid faults will be addressed.