Enhancing Controllability of Wind Farms Against Parametric Resonance: A Series Compensation Approach

A critical factor deciding the controllability of a doubly-fed induction generator (DFIG) in a wind power system is the ratio of its leakage reactance to resistance. If this ratio is high then the DFIG has two uncontrollable slow resonant modes. The emergence of these modes, often referred to as parametric resonance, can cause the wind farm to exhibit poorly damped transient behavior, irrespective of any control action. In this letter we resolve this problem by presenting a new series compensation strategy in the stator line of the DFIG that prevents this uncontrollability. By tuning the compensation and the controller gains of the DFIG, the controllability of the wind farm is shown to be improved drastically, and accordingly the inter-area oscillations on the grid side to be damped significantly. We illustrate various implementation aspects of the proposed approach via numerical simulations of the IEEE 68-bus power system model with one wind farm.