Robust Active Damping Strategy for DFIG Wind Turbines

Doubly fed induction generators (DFIGs) with an
LCL
filter are widely used for wind power generation. In these energy conversion systems, there is an interaction between the grid-side converter (GSC) and the rotor-side converter (RSC) control loops, the generator and the
LCL
filter that must be properly modeled. Such interaction between the GSC and the RSC proves to have a significant influence on the stability. Several active damping (AD) methods for grid-connected converters with an
LCL
filter have been proposed, nevertheless, the application of these techniques to a DFIG wind turbine is not straightforward, as revealed in this article. To achieve a robust damping irrespective of the grid inductance, this article proposes an AD strategy based on the capacitor current feedback and the adjustment of the control delays to emulate a virtual impedance, in parallel with the filter capacitor, with a dominant resistive component in the range of possible resonance frequencies. This work also proves that, by applying the AD strategy in both converters simultaneously, the damping of the system resonant poles is maximized when a specific value of the grid inductance is considered. Experimental results show the interaction between the GSC and the RSC and validate the proposed AD strategy.