A Fault-Tolerant Control Paradigm for Microgrid-Connected Wind Energy Systems

Wind power is a promising alternative energy source; however, its integration to the microgrid is challenging and requires the consideration of voltage regulation, power quality, and voltage variations. This paper proposes a novel fault-tolerant control paradigm for a microgrid-connected doubly fed induction generator (DFIG)-based wind energy system to: 1) achieve ride through during any kind of voltage sag conditions including deep sags and 2) enable the strict satisfaction of recent grid code requirements. The proposed paradigm includes a novel integral terminal sliding mode controller (ITSMC) for the rotor- and grid-side converters along with a series grid-side converter (SGSC) to maintain the voltage levels across the stator windings at their prefault values. A fuzzy logic and a Posicast approach are also proposed to control the SGSC and further improve the performance of the wind energy system. The effectiveness of the proposed fault-tolerant configuration in riding through different types of grid faults is evaluated via detailed computer experiments. The merits of the proposed approach are further compared to those of the standard state of the art in voltage sag mitigation, namely, the shunt current injection approach and the dynamic voltage restorer. Results clearly show that the proposed control paradigm is able to protect the converters from damages and ensure continuous connection of the WT to the grid during faults, hence maintaining power quality.