Nonlinear control of wind energy conversion system based on DFIG with a mechanical torque observer

In this paper, an advanced nonlinear backstepping control approach is developed and applied to the whole nonlinear system including the AC/DC/AC converters combined with the doubly-fed induction generator(DFIG). A high gain observer is synthesized, in order to provide an estimated value of the mechanical torque whereas, a wind speed estimation block is designed based on roots polynomial method; followed by sensorless maximum power point tracking (MPPT). The control objectives are fourfold: (i) Forcing the generator speed to track the reference signal given by the MPPT block, (ii) adjusting the stator reactive power injected into the grid to be null, (iii) Regulating the DC-link voltage between the rotor side and the grid side converters at the desired level, (iv) assuring a unitary power factor in the grid side. The achievement of these control objectives leans on a multi-loop regulator which shows a satisfying performance as far as it concerns the simulation results.