A SCR crowbar commutated with power converter for DFIG-based wind turbines

Abstract

This paper presents an active crowbar, constructed with silicon controlled rectifiers (SCRs), for doubly fed induction generator (DFIG)-based wind turbines to fulfill low-voltage ride-through (LVRT) requirements demanded by grid codes. By this design, not only the active deactivation of the costly IGBT crowbar, replacing the passive crowbar for this ability, can be achieved with the more cost-effective SCRs, but also the reliability of the circuit is strengthened thanking to the high surge capability of SCR. In this topology, three back-to-back SCR switches are connected in delta form and further engaged with the rotor circuit of DFIG through power dissipation resistors, working as the main circuit of crowbar, while the rotor side converter (RSC) is used to commutate the SCRs at the desired deactivation moment to disconnect the crowbar, allowing for resumption of the feedback control to DFIG. By this topology the harmonics introduced into the rotor circuit by the diode bride in the IGBT crowbar are got rid of and by this commutation method the overvoltage risk at turning off the IGBT is eliminated. With the simulative results on a 2MW DFIG, the comparison with the IGBT crowbar is made. The feasibility of the proposed crowbar technique is further demonstrated with experiments on a laboratory-scale test rig.