Second-order sliding-mode controller design and tuning for grid synchronisation and power control of a wind turbine-driven doubly fed induction generator

This study presents a second-order sliding-mode control (2-SMC) scheme for a wind turbine-driven doubly fed induction generator (DFIG). The tasks of grid synchronisation and power control are undertaken by two different algorithms, designed to command the rotor-side converter at a fixed switching frequency. Effective tuning equations for the parameters of both controllers are derived. A procedure is also provided that guarantees bumpless transfer between the two controllers at the instant of connecting the DFIG to the grid. The resulting 2-SMC scheme is experimentally validated on a laboratory-scale 7 kW DFIG test bench. Experimental results evidence both the high dynamic performance and the superior robustness achieved with the proposed control scheme.