Control of a grid connected doubly-fed induction generators for wind energy conversion

With improved generator and turbine designs, better control techniques and low environmental impact, wind energy has emerged as a potential source of bulk power across the globe. In this paper, the authors report on the development of a variable speed controller for a doubly-fed induction generator (DFIG) based wind energy conversion system (WECS). DFIG is preferred as the generator because of several advantages such as high energy efficiency, robustness and easy controllability. Firstly, a mathematical model of the DFIG is developed in an appropriate d-q reference frame for simulation purpose. Secondly, the controller is designed to control the power exchange between the stator of the DFIG and the utility grid network. Two types of control strategies are considered - PI control and pitch angle (Pitch-to-feather) control. The respective performances of the two types of controllers are compared in terms of power reference tracking, response to sudden speed variations, sensitivity to perturbations and robustness against machine parameters variations.