Second-order sliding-mode-based global control scheme for wind turbine-driven DFIGs subject to unbalanced and distorted grid voltage

Abstract

Control algorithms for both the rotor- and grid-side power converters of a wind turbine-driven doubly-fed induction generator (DFIG) are detailed, and tuning equations are also provided to assist adjustment of their gains and constants. Those algorithms are based on the second-order sliding-mode control (2-SMC) approach, and they allow the wind turbine to satisfactorily operate under grid voltage non-idealities, such as simultaneously distorted and unbalanced scenarios. The presented solution turns out to be robust against parameter deviations and disturbances, and of high-performance dynamic response. Moreover, it drives the transistors of both power converters at a constant switching frequency, also avoiding decomposition in symmetrical sequences of either the grid voltage or currents. The controllers proposed for the two power converters are validated through experimentation on a 7-kW DFIG test bench subject to a significantly unbalanced and harmonically distorted grid voltage. Their robustness in the presence of both substantial parameter mismatch and disturbances attributable to wind variability is also assessed.