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Operation and control of a DFIG-based grid-connected WECS using NSC during grid fault and with unbalanced non-linear load

ABSTRACT This paper proposes a combined feed-forward and selective harmonic compensation-based control scheme for a grid-connected doubly fed induction generator Wind Turbine system using a nine-switch converter (NSC) to improve the performance during grid faults and unbalanced non-linear loading. This is achieved through desired line voltage compensation and/or selective harmonic reduction technique. The two outputs of NSC are controlled such that one functions as a series grid-side converter to inject appropriate voltage in series with stator terminals to maintain the desired stator voltage profile, while the other one functions as a parallel grid-side converter to regulate the DC-link voltage to its reference value irrespective of the direction of flow of rotor power with the conventional rotor side converter. Simulation has been carried out in a MATLAB/Simulink environment. The results show that the proposed scheme ensures the feasibility of improving the Fault Ride Through capability and reducing the undesirable effects of the unbalanced, harmonic content in grid voltage at the Point of Common Coupling.