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The authors propose robust non-linear controllers for a wind system. The proposed controllers are based on a combination of the block control linearisation and super-twisting algorithm, as a second-order sliding mode technique. The main control loop is designed to regulate the electromagnetic torque and stator power factor of a doubly-fed induction generator which is connected to the grid. The generator is mechanically coupled with a DC motor, which can emulate the wind turbine operation. Therefore, an auxiliary control loop is designed to control the DC motor velocity. Additionally, a grid-side converter controller is proposed to regulate the DC-link voltage into AC/DC/AC converter, and displacement factor of the energy flow between the rotor and the grid. A robust stability analysis of the complete closed-loop system under external disturbances is presented. The robustness of the proposed control schemes is validated in real time using a workbench, which consists of a motor-generator group, AC/DC/AC electronic drive and dSPACE DS 1104 controller boards.

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A method for identification of any even number of parameters of the transfer function from the test of the process, which involves application of the modified twisting algorithm, is proposed. Equations for determining the unknown parameters can be written separately for the magnitude and the argument of the transfer function that simplifies the task of the identification. As a result, the problem can be reduced to the iterative solution of a system of algebraic equations.

In this paper, a robust non-linear controller based on block control linearization combined with a second order sliding modes technique called super-twisting algorithm is proposed for controlling a wind power system. The control objectives consist on maximize the wind energy capture by the turbine and keep the stator power factor of a wound rotor induction generator in a set point value. The goal is achieved by controlling the rotor velocity and stator reactive power of the induction generator which is connected to an infinity bus and coupled with a wind turbine across a gear box. The performance of the designed controller is validated through simulations.

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