Control Strategies for Augmenting LVRT Capability of DFIGs in Interconnected Power Systems

This paper presents a new control scheme for the enhancement of the low-voltage ride-through (LVRT) capability of doubly fed induction generators. The LVRT capability is provided by extending the range of operation of the controlled system to include typical postfault conditions. Controllers are designed simultaneously for both the rotor- and grid-side converters using a linear quadratic output-feedback decentralized control strategy. The nonlinear terms in the power system model are represented in this paper by an uncertain term derived from the Cauchy remainder of the Taylor series expansion. A genetic algorithm is used to calculate the bound on the uncertainty. The robust controller resulting from this design provides acceptable performances to enhance voltage and transient stability margins and thereby to limit the oscillations, the peak value of the rotor current, and the dc-link voltage fluctuations. The performance of the designed controller is demonstrated under different operating conditions by large-disturbance simulations on a test system.