Selective harmonics compensation using a WECS equipped by a DFIG

Abstract

In this paper, a control strategy is proposed to enhance the capability in terms of active filtering, of a Wind Energy Conversion System (WECS) based on a Doubly Fed Induction Generator (DFIG). The stator of the DFIG is directly connected to the grid and the rotor is connected to the grid through a back to back AC-DC-AC PWM converter. The proposed algorithm is applied to the Rotor Side Converter (RSC) to achieve simultaneously the Maximum Power Point Tracking (MPPT) and the power quality improvement at the Point of Common Coupling (PCC). This enables the grid to supply only sinusoidal currents at Unity Power Factor (UPF). Depending on the nominal RSC power, reactive power of linear loads and harmonic currents due to the nonlinear loads can be compensated. The proposed RSC control strategy manages the WECS function's priorities between active power production, reactive power compensation and active filtering without any system over-rating. To enhance the capability of the RSC, in terms of active filtering, it is proposed to eliminate instantaneously the whole of the 5th and the 7th predominant harmonic components if possible, otherwise, the filtering operation is omitted. The Grid Side Converter (GSC) is controlled in such a way to guarantee a smooth DC voltage. The presented simulation results demonstrate the performance and the effectiveness of the proposed control strategy.