A SCR Crowbar Commutated with Rotor-Side Converter for Doubly Fed Wind Turbines

Doubly fed induction generator (DFIG) based wind turbines have been dominating wind market in the past decade, due to the better balance between variable speed operation and the drive converter size in terms of the unique drive topology. However, the difficulties of low voltage ride through (LVRT) fulfillment are threatening this type of turbine technology, out of the limits of current and voltage to the partial rated converter. Active crowbar at present is a relatively mature solution for severe voltage dips, but the requisite self-turn-off devices, typically IGBTs, have made the cost-effectiveness of this type of turbines damaged. Meanwhile, once the crowbar is activated, the rotor-side converter (RSC), along with all its six valuable selfturn- off IGBTs, would be idle temporarily. In this paper, a deltaconnected SCR circuit engaged with the rotor via a set of by-pass resistors is designed as a crowbar to divert the outrush currents, while the idle RSC is in charge of commutating the semicontrolled devices at the desired deactivation moment. With this design, an active crowbar function is achieved with SCRs, featured with low cost and high instantaneous overload capacity, benefiting the cost-performance ratio of the preferable wind turbine concept. Meanwhile, the harmful effects of the harmonics produced by the diode rectifier in the widely used IGBT crowbar topology are eliminated. The validity of the crowbar technique is demonstrated with simulations and experiments.