Unified Power Quality Conditioner With Advanced Dual Control for Performance Improvement of DFIG-Based Wind Farm

The weakness of low voltage ride-through capacity, power oscillations under asymmetrical fault and the instability of the output power are three major difficulties that need to be urgently addressed in the field of doubly fed induction generator (DFIG). To simultaneously deal with these issues, this article proposes a cost-effective energy storage device-based unified power quality conditioner (ESD-UPQC) to improve the low voltage ride through capability of the DFIG, suppress voltage oscillations under unbalanced faults and regulate DFIG output power during fluctuated wind speed conditions. A comprehensive protection scheme is carried out that the series side converter of the ESD-UPQC is controlled using dual control to suppress the post-fault voltage oscillations under transient conditions, while three advanced control targets are proposed for the parallel side converter aiming at regulating DFIG output power during wind gust, and suppress power oscillations during symmetrical and asymmetrical grid faults. Simulation results attest the feasibility of the proposed controller. The robustness of the proposed ESD-UPQC controller is validated through a series of comparisons based on a lead-acid battery scheme and an ESD-DFIG scheme for power smoothing and LVRT enhancement respectively.