Variable speed control of DFIG-wind turbine with wind estimation

This paper deals with the problem of controlling aeorogenerators consisting of a doubly fed induction generator (DFIG) coupled to a wind turbine. It is well known that fixed speed operation entails nonoptimal energetic efficiency of the aerogenerator. Various solutions have been proposed to achieve an optimal varying speed control. However, in most controllers it is require that wind speed distribution along the turbine blades is known. The point is that reliable wind speed sensors for turbines are not available. In this work, a nonlinear control law of variable speed wind energy is developed using Backstepping approach that involves online wind speed estimation based on an energy balance of the generator. The control objective is threefold: (i) tracking the maximum available wind power to ensure the achievement of maximum power point (MPPT) based on the wind speed estimate; (ii) regulating the rotor flux by controlling the stator reactive power; (iii) ensuring the constant DC link voltage. The performances of the wind estimator as well as the control laws are validated by simulation studies with Matlab/Simulink® environment.