Virtual torque control in wind generation with doubly fed induction generator

In this work, a controller design strategy for wind turbines with doubly fed induction generators is addressed. The goal of the controller is to assure bounded both power derivative and blade pitch angle derivative, at the same time that the accelerations of the machine are minimized in order to avoid harmful fatigue loads. A time-varying gain state feedback controller with observer is proposed, where the gain depends on the mean wind and the turbulence intensity level. The design of the controller has been addressed through ℒ₁ optimization procedures. The controller output is the total amount of desired torque variation, that is then distributed between the manipulated signals (blade pitch angle and electromagnetic torque). An observer has also been added to estimate the state, the instantaneous wind speed, its mean and its turbulence intensity level, as needed by the proposed controller.