Crowbar resistors are three phase resistance banks which are connected to the rotor windings of the DFIG (Doubly-Feed Induction Generator) such as wind power generator.
They are used to prevent damage to the inverter circuits attached to rotor side when a fault occurs in the grid. DFIG power converter, which has a restricted over-current limit, needs special attention during faults in the grid. If the rotor current or DC link voltage reaches the threshold value, crowbar resistors disconnect the converter in order to prevent the generator turning into a squirrel cage induction machine. By crowbar resistors, the DFIG could stay connected to the grid and continue its operation.
The crowbar resistors should be high enough to limit the short circuit rotor current and also they should be low enough to avoid too high voltage in the rotor circuit. The crowbar resistor should be designed with low inductance and capable of handling very high currents for short periods.